Virus World

Health department says it's working with Jerusalem 'to ensure a coordinated response' after 4 cases of virus recently detected in Safed. The State of New York’s health department called for residents to get vaccinated against polio before traveling to Israel, where several children have recently tested positive for the virus. In a statement Friday, the New York Department of Health noted the four cases diagnosed in the northern city of Safed earlier this month, a year after a small outbreak of the disease in the country. It called on New Yorkers “to get fully immunized” before flying to Israel or other countries with polio. Health officials in New York have been in touch with their Israeli counterparts “to ensure a coordinated response,” the statement said, adding that travelers should adhere to guidelines from the US Center for Disease Control. Besides Israel, the statement noted the CDC has issued precautions against polio before traveling to the United Kingdom, Ukraine, Afghanistan, Pakistan, Indonesia, Nigeria, Côte d’Ivoire and several other central African countries.

Polio is a viral disease that mainly affects children and can cause disability, paralysis and death. Today, polio vaccinations are standard for children and are an effective preventive measure, but vaccine skepticism has enabled the disease to pop up from time to time. The outbreak in Israel last March, which came after the first case of polio in 33 years was discovered in the country, prompted a vaccination drive to combat the disease. The finding landed Israel on the World Health Organization’s Polio Eradication Initiative’s list of countries with outbreaks, after it was declared polio-free in 1988. Following the cases detected earlier this month, the Health Ministry cited evidence of polio spreading in sewage systems and said over 150,000 Israeli children are unvaccinated against the virus.

Evidence from sewage reveals resilience of last year’s coronavirus killer, indicating a possible outbreak of Delta or another variant this summer.  Just when we thought we were out of the Covid woods, researchers at Ben-Gurion University of the Negev are sounding the alarm. Omicron, the variant that evolved to be somewhat less deadly than previous Covid flavors, may burn itself out in the next couple of months. Omicron and its sub-variants (BA.2, BA.3, BA.4, BA.5 and presumably more on the way) have been so contagious that the previous big bad – Delta – was thought to be wiped out. 

A Fourth Dose of mRNA Vaccine in Health Care Workers Health care workers in Israel were given a fourth dose of BNT162b2 or mRNA-1273 vaccine during a period of omicron-variant predominance. Level. In this open-label, nonrandomized clinical study, we assessed the immunogenicity and safety of a fourth dose of either BNT162b2 (Pfizer–BioNTech) or mRNA-1273 (Moderna) administered 4 months after the third dose in a series of three BNT162b2 doses (ClinicalTrials.gov numbers, NCT05231005. opens in new tab and NCT05230953. opens in new tab; the protocol is available with the full text of this letter at NEJM.org). Of the 1050 eligible health care workers enrolled in the Sheba HCW COVID-19 Cohort, 154 received the fourth dose of BNT162b2 and, 1 week later, 120 received mRNA-1273. For each participant, two age-matched controls were selected from the remaining eligible participants (Fig. S1 in the Supplementary Appendix, available at NEJM.org). 

After the fourth dose, both messenger RNA (mRNA) vaccines induced IgG antibodies against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) receptor-binding domain and increased neutralizing antibody titers (Fig. S3); each measure was increased by a factor of 9 to 10, to titers that were slightly higher than those achieved after the third dose, with no significant difference between the two vaccines. Concurrently, antibody levels in the control group continued to wane (Table S5). Both vaccines induced an increase in live neutralization of the B.1.1.529 (omicron) variant and other viral strains by a factor of approximately 10 , similar to the response after the third dose. We found that the fourth dose did not lead to substantial adverse events despite triggering mild systemic and local symptoms in the majority of recipients (Fig. S2 and Table S4A and S4B).  Because of the extremely high infection incidence and meticulous active surveillance with weekly SARS-CoV-2 polymerase-chain-reaction testing, we were also able to assess vaccine efficacy with a Poisson regression model (see the Supplementary Appendix). Overall, 25.0% of the participants in the control group were infected with the omicron variant, as compared with 18.3% of the participants in the BNT162b2 group and 20.7% of those in the mRNA-1273 group. Vaccine efficacy against any SARS-CoV-2 infection was 30% (95% confidence interval [CI], −9 to 55) for BNT162b2 and 11% (95% CI, −43 to 44) for mRNA-1273. Most infected health care workers reported negligible symptoms, both in the control group and the intervention groups. However, most of the infected participants were potentially infectious, with relatively high viral loads (nucleocapsid gene cycle threshold, ≤25) (Table S6). Vaccine efficacy was estimated to be higher for the prevention of symptomatic disease (43% for BNT162b2 and 31% for mRNA-1273) (Fig. S4).

Limitations of the study include its nonrandomized design and the 1-week difference between enrollment in the two intervention groups, generating potential biases. To overcome this, we assessed each intervention group separately and used a Poisson model accounting for calendar time. In addition, despite similar requests for weekly SARS-CoV-2 testing, adherence was slightly lower in the control group. We did not sequence the infecting virus and cannot be absolutely certain that all cases were caused by the omicron variant; however, during the study period, omicron accounted for 100% of the isolates that were typed. Finally, our cohort was too small to allow for accurate determination of vaccine efficacy. However, within the wide confidence intervals of our estimates, vaccine efficacy against symptomatic disease was 65% at most. Our data provide evidence that a fourth dose of mRNA vaccine is immunogenic, safe, and somewhat efficacious (primarily against symptomatic disease). A comparison of the initial response to the fourth dose with the peak response to a third dose did not show substantial differences in humoral response or in levels of omicron-specific neutralizing antibodies. Along with previous data showing the superiority of a third dose to a second dose, our results suggest that maximal immunogenicity of mRNA vaccines is achieved after three doses and that antibody levels can be restored by a fourth dose. Furthermore, we observed low vaccine efficacy against infections in health care workers, as well as relatively high viral loads suggesting that those who were infected were infectious. Thus, a fourth vaccination of healthy young health care workers may have only marginal benefits. Older and vulnerable populations were not assessed.

Published in NEJM (March 16, 2022):

https://doi.org/10.1056/NEJMc2202542

BACKGROUND

The emergence of the B.1.617.2 (delta) variant of severe acute respiratory syndrome coronavirus 2 and the reduced effectiveness over time of the BNT162b2 vaccine (Pfizer–BioNTech) led to a resurgence of coronavirus disease 2019 (Covid-19) cases in populations that had been vaccinated early. On July 30, 2021, the Israeli Ministry of Health approved the use of a third dose of BNT162b2 (booster) to cope with this resurgence. Evidence regarding the effectiveness of the booster in lowering mortality due to Covid-19 is still needed.

METHODS

We obtained data for all members of Clalit Health Services who were 50 years of age or older at the start of the study and had received two doses of BNT162b2 at least 5 months earlier. The mortality due to Covid-19 among participants who received the booster during the study period (booster group) was compared with that among participants who did not receive the booster (nonbooster group). A Cox proportional-hazards regression model with time-dependent covariates was used to estimate the association of booster status with death due to Covid-19, with adjustment for sociodemographic factors and coexisting conditions.

RESULTS

A total of 843,208 participants met the eligibility criteria, of whom 758,118 (90%) received the booster during the 54-day study period. Death due to Covid-19 occurred in 65 participants in the booster group (0.16 per 100,000 persons per day) and in 137 participants in the nonbooster group (2.98 per 100,000 persons per day). The adjusted hazard ratio for death due to Covid-19 in the booster group, as compared with the nonbooster group, was 0.10 (95% confidence interval, 0.07 to 0.14; P<0.001).

CONCLUSIONS

Participants who received a booster at least 5 months after a second dose of BNT162b2 had 90% lower mortality due to Covid-19 than participants who did not receive a booster.

Published in NEJM (Dec. 8, 2021):

https://doi.org/10.1056/NEJMoa2115624  

A new study from Israel and the U.S. found the risk of infection was 2.37-fold higher between 90 and 119 days after completing the vaccine series compared to the initial 90 days.

• A new study looked at more than 80,000 adults who were fully vaccinated with the Pfizer-BioNTech vaccine
• The percentage of tests that came back positive increased from 1.3% prior to 90 days to of 2.4% 90 to 119 days later, to 10.3% 150 to 179 days later 
• Risk of infection was 2.37-fold higher between 90 and 119 days after completing the vaccine series compared to the initial 90 days
• This increased to a 2.82-fold increased risk 180 days or more after receiving the second dose
• Researchers say the findings show booster shots are likely needed to sustain long-term protection from Covid

Immunity against infection from COVID-19 vaccines is waning over time, a new study suggests. Researchers from the Leumit Health Services in Israel and the U.S. National Institutes of Health (NIH) looked at people inoculated with the Pfizer-BioNTech vaccine. They found that, 90 days after receiving the second dose, the risk of contracting the virus more than doubles and only keeps increasing as far as six months out.  What's more, the percentage of tests coming back positive for COVID-19 quadrupled from 2.4 percent at least 90 days later to 10.6 percent at least 150 days later. The finding add more evidence that, while the Pfizer vaccines provides strong protection in the initial weeks, booster shots are likely needed to sustain long-term protection from Covid.   Israel was one of the first countries to roll out use of Pfizer's Covid vaccine in December 2020 and the U.S. was not far behind. The Middle Eastern country experienced a resurgence in cases in September while infections are creeping up now in the U.S. This has led many experts to fear that immunity from the standard two-dose regimen wanes over time.  Researchers say determining the risk of infection as more time elapses since dose two can lead to important information about the optimal timing of a third dose.  

For the study, published in The BMJ, the team looked at the electronic health records of 80,057 adults in Israel. All of the adults were fully vaccinated with the Pfizer shot and had no history of a prior COVID-19 infection.  Of this group, 7,973 - or 9.6 percent - ended up testing positive for COVID-19. After matching patients to controls that were of the same age and racial/ethnic background, researchers found the rate of positive Covid tests increased the more time had passed since the second dose. Between 21 and 89 days after the second dose, only 1.3 percent of tests came back positive. However, between 90 and 119 days later, this rate nearly doubled to 2.4 percent, and only continued to grow. A total of 4.6 percent of tests came back positive 120 to 149 days after the second dose, increasing to 10.3 percent 150 to 179 days later and to 18.5 percent 180 days or more later.  Next, researchers looked at the risk of infection across all age groups compared to 90 days after the second dose. They found that the risk of infection with 2.37-fold higher between 90 and 119 days after completing the vaccine series. This only continued to increase to  2.66-fold higher after 120 to 149 days; 2.82-fold higher after 150 to 179 days; and 2.82-fold higher after 180 days or beyond.

Cited study Published in BMJ (Nov. 25, 2021):

 https://doi.org/10.1136/bmj-2021-067873 

BACKGROUND

Reports have suggested an association between the development of myocarditis and the receipt of messenger RNA (mRNA) vaccines against coronavirus disease 2019 (Covid-19), but the frequency and severity of myocarditis after vaccination have not been extensively explored.

METHODS

We searched the database of Clalit Health Services, the largest health care organization (HCO) in Israel, for diagnoses of myocarditis in patients who had received at least one dose of the BNT162b2 mRNA vaccine (Pfizer–BioNTech). The diagnosis of myocarditis was adjudicated by cardiologists using the case definition used by the Centers for Disease Control and Prevention. We abstracted the presentation, clinical course, and outcome from the patient’s electronic health record. We performed a Kaplan–Meier analysis of the incidence of myocarditis up to 42 days after the first vaccine dose.

RESULTS

Among more than 2.5 million vaccinated HCO members who were 16 years of age or older, 54 cases met the criteria for myocarditis. The estimated incidence per 100,000 persons who had received at least one dose of vaccine was 2.13 cases (95% confidence interval [CI], 1.56 to 2.70). The highest incidence of myocarditis (10.69 cases per 100,000 persons; 95% CI, 6.93 to 14.46) was reported in male patients between the ages of 16 and 29 years. A total of 76% of cases of myocarditis were described as mild and 22% as intermediate; 1 case was associated with cardiogenic shock. After a median follow-up of 83 days after the onset of myocarditis, 1 patient had been readmitted to the hospital, and 1 had died of an unknown cause after discharge. Of 14 patients who had left ventricular dysfunction on echocardiography during admission, 10 still had such dysfunction at the time of hospital discharge. Of these patients, 5 underwent subsequent testing that revealed normal heart function.

CONCLUSIONS

Among patients in a large Israeli health care system who had received at least one dose of the BNT162b2 mRNA vaccine, the estimated incidence of myocarditis was 2.13 cases per 100,000 persons; the highest incidence was among male patients between the ages of 16 and 29 years. Most cases of myocarditis were mild or moderate in severity. (Funded by the Ivan and Francesca Berkowitz Family Living Laboratory Collaboration at Harvard Medical School and Clalit Research Institute.)

Published in NEJM (Oct. 6, 2021):

https://doi.org/10.1056/NEJMoa2110737 

BACKGROUND

Despite the high efficacy of the BNT162b2 messenger RNA vaccine against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), rare breakthrough infections have been reported, including infections among health care workers. Data are needed to characterize these infections and define correlates of breakthrough and infectivity.

METHODS

At the largest medical center in Israel, we identified breakthrough infections by performing extensive evaluations of health care workers who were symptomatic (including mild symptoms) or had known infection exposure. These evaluations included epidemiologic investigations, repeat reverse-transcriptase–polymerase-chain-reaction (RT-PCR) assays, antigen-detecting rapid diagnostic testing (Ag-RDT), serologic assays, and genomic sequencing. Correlates of breakthrough infection were assessed in a case–control analysis. We matched patients with breakthrough infection who had antibody titers obtained within a week before SARS-CoV-2 detection (peri-infection period) with four to five uninfected controls and used generalized estimating equations to predict the geometric mean titers among cases and controls and the ratio between the titers in the two groups. We also assessed the correlation between neutralizing antibody titers and N gene cycle threshold (Ct) values with respect to infectivity.

RESULTS

Among 1497 fully vaccinated health care workers for whom RT-PCR data were available, 39 SARS-CoV-2 breakthrough infections were documented. Neutralizing antibody titers in case patients during the peri-infection period were lower than those in matched uninfected controls (case-to-control ratio, 0.361; 95% confidence interval, 0.165 to 0.787). Higher peri-infection neutralizing antibody titers were associated with lower infectivity (higher Ct values). Most breakthrough cases were mild or asymptomatic, although 19% had persistent symptoms (>6 weeks). The B.1.1.7 (alpha) variant was found in 85% of samples tested. A total of 74% of case patients had a high viral load (Ct value, <30) at some point during their infection; however, of these patients, only 17 (59%) had a positive result on concurrent Ag-RDT. No secondary infections were documented.

CONCLUSIONS

Among fully vaccinated health care workers, the occurrence of breakthrough infections with SARS-CoV-2 was correlated with neutralizing antibody titers during the peri-infection period. Most breakthrough infections were mild or asymptomatic, although persistent symptoms did occur.

Published in NEJM (July 28, 2021):

https://doi.org/10.1056/NEJMoa2109072 

BACKGROUND

Preapproval trials showed that messenger RNA (mRNA)–based vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) had a good safety profile, yet these trials were subject to size and patient-mix limitations. An evaluation of the safety of the BNT162b2 mRNA vaccine with respect to a broad range of potential adverse events is needed.

METHODS

We used data from the largest health care organization in Israel to evaluate the safety of the BNT162b2 mRNA vaccine. For each potential adverse event, in a population of persons with no previous diagnosis of that event, we individually matched vaccinated persons to unvaccinated persons according to sociodemographic and clinical variables. Risk ratios and risk differences at 42 days after vaccination were derived with the use of the Kaplan–Meier estimator. To place these results in context, we performed a similar analysis involving SARS-CoV-2–infected persons matched to uninfected persons. The same adverse events were studied in the vaccination and SARS-CoV-2 infection analyses.

RESULTS

In the vaccination analysis, the vaccinated and control groups each included a mean of 884,828 persons. Vaccination was most strongly associated with an elevated risk of myocarditis (risk ratio, 3.24; 95% confidence interval [CI], 1.55 to 12.44; risk difference, 2.7 events per 100,000 persons; 95% CI, 1.0 to 4.6), lymphadenopathy (risk ratio, 2.43; 95% CI, 2.05 to 2.78; risk difference, 78.4 events per 100,000 persons; 95% CI, 64.1 to 89.3), appendicitis (risk ratio, 1.40; 95% CI, 1.02 to 2.01; risk difference, 5.0 events per 100,000 persons; 95% CI, 0.3 to 9.9), and herpes zoster infection (risk ratio, 1.43; 95% CI, 1.20 to 1.73; risk difference, 15.8 events per 100,000 persons; 95% CI, 8.2 to 24.2). SARS-CoV-2 infection was associated with a substantially increased risk of myocarditis (risk ratio, 18.28; 95% CI, 3.95 to 25.12; risk difference, 11.0 events per 100,000 persons; 95% CI, 5.6 to 15.8) and of additional serious adverse events, including pericarditis, arrhythmia, deep-vein thrombosis, pulmonary embolism, myocardial infarction, intracranial hemorrhage, and thrombocytopenia.

CONCLUSIONS

In this study in a nationwide mass vaccination setting, the BNT162b2 vaccine was not associated with an elevated risk of most of the adverse events examined. The vaccine was associated with an excess risk of myocarditis (1 to 5 events per 100,000 persons). The risk of this potentially serious adverse event and of many other serious adverse events was substantially increased after SARS-CoV-2 infection. (Funded by the Ivan and Francesca Berkowitz Family Living Laboratory Collaboration at Harvard Medical School and Clalit Research Institute.)

Published in New England J. Medicine (August 25, 2021):

https://doi.org/10.1056/NEJMoa2110475

With early vaccination and outstanding data, country is the world’s real-life COVID-19 lab. “Now is a critical time,” Israeli Minister of Health Nitzan Horowitz said as the 56-year-old got a COVID-19 booster shot on 13 August, the day his country became the first nation to offer a third dose of vaccine to people as young as age 50. “We’re in a race against the pandemic.”  His message was meant for his fellow Israelis, but it is a warning to the world. Israel has among the world’s highest levels of vaccination for COVID-19, with 78% of those 12 and older fully vaccinated, the vast majority with the Pfizer vaccine. Yet the country is now logging one of the world’s highest infection rates, with nearly 650 new cases daily per million people. More than half are in fully vaccinated people, underscoring the extraordinary transmissibility of the Delta variant and stoking concerns that the benefits of vaccination ebb over time. The sheer number of vaccinated Israelis means some breakthrough infections were inevitable, and the unvaccinated are still far more likely to end up in the hospital or die. But Israel’s experience is forcing the booster issue onto the radar for other nations, suggesting as it does that even the best vaccinated countries will face a Delta surge.  His message was meant for his fellow Israelis, but it is a warning to the world. Israel has among the world’s highest levels of vaccination for COVID-19, with 78% of those 12 and older fully vaccinated, the vast majority with the Pfizer vaccine. Yet the country is now logging one of the world’s highest infection rates, with nearly 650 new cases daily per million people. More than half are in fully vaccinated people, underscoring the extraordinary transmissibility of the Delta variant and stoking concerns that the benefits of vaccination ebb over time. The sheer number of vaccinated Israelis means some breakthrough infections were inevitable, and the unvaccinated are still far more likely to end up in the hospital or die.

But Israel’s experience is forcing the booster issue onto the radar for other nations, suggesting as it does that even the best vaccinated countries will face a Delta surge. At the same time, cases in the country, which were scarcely registering at the start of summer, have been doubling every week to 10 days since then, with the Delta variant responsible for most of them. They have now soared to their highest level since mid-February, with hospitalizations and intensive care unit admissions beginning to follow. How much of the current surge is due to waning immunity versus the power of the Delta variant to spread like wildfire is uncertain. What is clear is that “breakthrough” cases are not the rare events the term implies. As of 15 August, 514 Israelis were hospitalized with severe or critical COVID-19, a 31% increase from just 4 days earlier. Of the 514, 59% were fully vaccinated. Of the vaccinated, 87% were 60 or older. “There are so many breakthrough infections that they dominate and most of the hospitalized patients are actually vaccinated,” says Uri Shalit, a bioinformatician at the Israel Institute of Technology (Technion) who has consulted on COVID-19 for the government. “One of the big stories from Israel [is]: ‘Vaccines work, but not well enough.’” “The most frightening thing to the government and the Ministry of Health is the burden on hospitals,” says Dror Mevorach, who cares for COVID-19 patients at Hadassah Hospital Ein Kerem and advises the government. At his hospital, he is lining up anesthesiologists and surgeons to spell his medical staff in case they become overwhelmed by a wave like January’s, when COVID-19 patients filled 200 beds. “The staff is exhausted,” he says, and he has restarted a weekly support group for them “to avoid some kind of PTSD [post-traumatic stress disorder] effect.”

To try to tame the surge, Israel has turned to booster shots, starting on 30 July with people 60 and older and, last Friday, expanding to people 50 and older. As of Monday, nearly 1 million Israelis had received a third dose, according to the Ministry of Health. Global health leaders including Tedros Adhanom Ghebreyesus, director-general of the World Health Organization, have pleaded with developed countries not to administer boosters given that most of the world’s population hasn’t received even a single dose. The wealthy nations pondering or already administering booster vaccines so far mostly reserve them for special populations such as the immune compromised and health care workers. Still, studies suggest boosters might have broader value. Researchers have shown that boosting induces a prompt surge in antibodies, which are needed in the nose and throat as a crucial first line of defense against infection. The Israeli government’s decision to start boosting those 50 and older was driven by preliminary Ministry of Health data indicating people over age 60 who have received a third dose were half as likely as their twice-vaccinated peers to be hospitalized in recent days, Mevorach says. CHS also reported that out of a sample of more than 4500 patients who received boosters, 88% said any side effects from the third shot were no worse, and sometimes milder, than from the second. Yet boosters are unlikely to tame a Delta surge on their own, says Dvir Aran, a biomedical data scientist at Technion. In Israel, the current surge is so steep that “even if you get two-thirds of those 60-plus [boosted], it’s just gonna give us another week, maybe 2 weeks until our hospitals are flooded.” He says it’s also critical to vaccinate those who still haven’t received their first or second doses, and to return to the masking and social distancing Israel thought it had left behind—but has begun to reinstate. Aran’s message for the United States and other wealthier nations considering boosters is stark: “Do not think that the boosters are the solution.”

Israel's Prime Minister has announced a program to roll out a third dose of the coronavirus vaccine to people over the age of 60, becoming one of the first countries in the world to make such a move.  People over 60 will need to show they received their second dose of the vaccine at least five months ago. Thursday's announcement follows a strong recommendation from the government-appointed team of experts on the pandemic to offer older adults a third dose. The experts' advice, which came overnight on Wednesday, was based on data suggesting significant waning immunity from infection over time. Some of the data considered by the health ministry comes from research on the "justification, safety and efficacy" of a third dose of the Pfizer-BioNTech vaccine for hemodialysis patients that was posted as a pre-print paper earlier this month.  The research found that about two-thirds of hemodialysis patients (people who require the procedure to remove waste products and excess fluid from the blood when the kidneys stop working properly) who had a suboptimal immune response after a second dose of the vaccine developed "optimal" antibodies and T cells after a third dose. From Tuesday to Thursday, the number of new cases in Israel has topped two thousand each day -- levels that have not been seen in the country for four and half months. Back in May and June, the number of new daily cases was down to single figures on some days.

While all participants in the control group displayed a positive antibody response to spike protein, only 51 of the 136 (37.5%) organ transplant recipients had positive serology. Researchers have found that organ transplant recipients may remain at high risk for COVID-19 even after being fully vaccinated against the novel coronavirus. The Israeli study analyzed the humoral responses of 139 kidney transplant recipients after receiving both shots of the Pfizer-BioNTech vaccine, benchmarking their results against a control group of 25 healthy participants. Across the board, the mean antibody levels "were significantly lower" in comparison to the control participants, the researchers said. Transplant recipients who did in fact display a positive serology were typically younger than those without. Additionally, the longer period of time between transplantation and vaccination was "significantly associated" with positive serological response to mRNA vaccines.

"The most significant predictors of failure to mount a humoral response in our cohort of kidney transplant recipients were advanced age, need for high dose corticosteroids during the last (pre-vaccination) year, maintenance with three immunosuppressive medications, and a regimen that includes [Mycophenolate mofetil] MMF," the study authors wrote. Researchers added that MMF is known to have a "suppressive effect on the immune system, including inhibition of antibody production," noting that "the greater the degree of immunosuppression, the less likely the patient will respond to immunization."  Out of the 139 study participants, only two developed severe COVID-19 infections following a full vaccination. One required severe hospitalization 12 weeks after being vaccinated, and the other died, nine weeks after receiving the second dose of the Pfizer vaccine.

Vaccinating many people against SARS-CoV-2 could stall infection rates even among unvaccinated children in the same community. Last December, Israel launched one of the fastest vaccination schemes in the world, reaching 50% of the population in 9 weeks. But only people aged 16 and over were eligible for the jab.

To test the ripple effects of widespread vaccination, Tal Patalon at Maccabi Healthcare Services in Tel Aviv-Yafo, Israel, Roy Kishony at the Technion — Israel Institute of Technology in Haifa and their colleagues analysed COVID-19 vaccinations and test results recorded between January and March 2021 for people in 223 Israeli communities (O. Milman et al. Preprint at medRxiv https://doi.org/f4d7; 2021). In each community, the authors examined the relationship between the vaccination rate in adults over three 3-week intervals and the rate of positive results for a COVID-19 test in children 35 days later. The authors found that, in the weeks after older people had received the Pfizer–BioNTech vaccine, the infection risk among children under 16 dropped proportionally to the percentage of adults who had been vaccinated. The authors warn that their results might be influenced by children who had previously been infected, even though the study included communities with low infection rates. The findings have not yet been peer reviewed.

Preprint available in medRxiv (March 31, 2021):

https://doi.org/10.1101/2021.03.26.21254394 

Maccabi health fund releases preliminary results of a study comparing vaccinated and not vaccinated members’ likability to contract the disease and said vaccine 92% effective.  A total of 371 out of 715,425 Israelis who passed at least a week after receiving two doses of the Pfizer coronavirus vaccine have contracted the virus – 0.04%, with 16 being sent to the hospital – according to a Health Ministry report released on Thursday. Immunity to COVID-19 is supposed to kick in a week after receiving the second dose of the Pfizer vaccine. According to the studies conducted by Pfizer, the vaccine had an efficacy of about 95%, which is considered very high. The Israeli data appear to confirm the inoculation’s effectiveness, showing an even more promising result. Later in the day, Maccabi Healthcare Services – one of the country’s four health maintenance organizations – released the first results of the vaccination campaign of its members, with the organization also comparing the data to a control group that did not get inoculated.

Background: During Late 2022, the SARS-CoV-2 Omicron BA.5 sublineages accounted for most of the sequenced viral genomes worldwide. Bivalent mRNA vaccines contain an ancestral SARS-CoV-2 strain component plus an updated component of the Omicron BA.4/BA.5. Since September 2022, a single bivalent booster dose has been recommended for adults who have completed a primary vaccination series and are at high risk for severe Covid-19 disease. Evidence regarding the effectiveness of the bivalent vaccine in reducing hospitalizations and death due to Covid-19 is warranted.

Methods: This retrospective cohort study included all members of Clalit Health Services, aged ≥65, eligible for a bivalent booster. Hospitalizations and death due to Covid-19 among participants who received the bivalent vaccine were compared with those who did not. A Cox proportional-hazards regression model with time-dependent covariates was used to estimate the association between the bivalent vaccine and Covid-19 outcomes while adjusting for demographic factors and coexisting illnesses.

Findings: A total of 622,701 participants met the eligibility criteria. Of those, 85,314 (14%) received a bivalent-booster during the 70-day study period. Hospitalization due to Covid-19 occurred in 6 bivalent recipients and 297 participants who did not, adjusted hazard ratio (HR): 0.19 (95% CI, 0.08-0.43). Death due to Covid-19 occurred in 1 bivalent recipient and 73 participants who did not, adjusted HR 0.14: (95% CI, 0.02-1.04).

Interpretation: Participants who received the bivalent vaccine had lower hospitalization and mortality rates due to Covid-19 than non-recipients up to 70 days after vaccination.
Funding Information: None.

Preprint available at the Lancet:

https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4314067 

With six confirmed and two suspected cases, health officials are ramping up a vaccination push amid fears of a wider outbreak.  A polio outbreak centered in Jerusalem has prompted Israel’s return to the World Health Organization’s list of polio “outbreak countries.” Israel now appears along with 28 other countries on the WHO’s Global Polio Eradication Initiative’s list of countries with polio outbreaks, after being declared polio-free in 1988. Nations including Egypt, Iran, Ethiopia and Ukraine are also on the list of outbreak countries — places where the virus was halted but has resurfaced — while Afghanistan and Pakistan are considered endemic countries. Last month, the first case of polio in more than 30 years was confirmed in Jerusalem, spurring deep concerns and a renewed vaccination drive.  According to the latest Health Ministry figures, released last week, there have been six confirmed polio cases, all among unvaccinated patients. In addition, there is a high likelihood of another case in an unvaccinated child, and an eighth potential case that is being investigated. Traces of the disease have also been found in the sewage system in Jerusalem, Beit Shemesh, Tiberias and Modiin Illit.

Over the past month, more than 18,000 children in the Jerusalem area have received a polio vaccine dose as part of the ministry’s push to reach those who were unvaccinated or partially vaccinated. Like much of the world, Israel administers polio vaccines — spread out in multiple doses — to children as part of its standard vaccine regimen. Polio spreads mostly from person to person or through contaminated water. It attacks the nervous system and can sometimes paralyze people within hours. The disease mostly affects children under 5 and has been largely wiped out in wealthy countries. Dr. Sharon Alroy-Preis, the Health Ministry’s public health director, explained last week that during the years 2005-2013, polio vaccinations were scaled back as the disease was vanquished in the country and many babies did not get all the necessary doses. “We are definitely seeing an outbreak of polio in Israel,” Alroy-Preis said. “It reaches unvaccinated pockets and is spreading.” One Jerusalem child who was recently diagnosed with polio has weakness and paralysis on one side, she reported. “That is just the tip of the iceberg, under which there are many other infected children,” she assessed. Disease experts have warned of the real prospect of a resurgence of polio cases — in manageable numbers but enough to leave some children with long-term damage. Traces of the virus have occasionally been found in sewage samples in Israel, but have not resulted in any clinical cases for several decades.

So far, Israel has registered four cases infected with the new variant, while general morbidity remains low.  There are indications that individuals fully vaccinated against corona within six months or with the booster are also protected against the Omicron variant, Health Minister Nitzan Horowitz said on Tuesday, after another two cases were identified, bringing the total to four. “In the coming days we will have more accurate information about the efficacy of the vaccine against Omicron, but there is already room for optimism, and there are initial indications that those who are vaccinated with a vaccine still valid or with a booster will also be protected from this variant,” Horowitz said while visiting the Soroka Medical Center in Beersheba with Finance Minister Avigdor Liberman.  There are indications that individuals fully vaccinated against corona within six months or with the booster are also protected against the Omicron variant, Health Minister Nitzan Horowitz said on Tuesday, after another two cases were identified, bringing the total to four. “In the coming days we will have more accurate information about the efficacy of the vaccine against Omicron, but there is already room for optimism, and there are initial indications that those who are vaccinated with a vaccine still valid or with a booster will also be protected from this variant,” Horowitz said while visiting the Soroka Medical Center in Beersheba with Finance Minister Avigdor Liberman.  Later in the evening, a report by Channel 12 said the Pfizer vaccine is just slightly less effective in preventing infection with Omicron than with Delta – 90% as opposed to 95% – while it is as effective – around 93% – in preventing serious symptoms at least for those vaccinated with a booster. According to the report, the ability of the variant to infect is higher than Delta but not as much as feared – around 1.3 times higher.

BACKGROUND

Despite high vaccine coverage and effectiveness, the incidence of symptomatic infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been increasing in Israel. Whether the increasing incidence of infection is due to waning immunity after the receipt of two doses of the BNT162b2 vaccine is unclear.

METHODS

We conducted a 6-month longitudinal prospective study involving vaccinated health care workers who were tested monthly for the presence of anti-spike IgG and neutralizing antibodies. Linear mixed models were used to assess the dynamics of antibody levels and to determine predictors of antibody levels at 6 months.

RESULTS

The study included 4868 participants, with 3808 being included in the linear mixed-model analyses. The level of IgG antibodies decreased at a consistent rate, whereas the neutralizing antibody level decreased rapidly for the first 3 months with a relatively slow decrease thereafter. Although IgG antibody levels were highly correlated with neutralizing antibody titers (Spearman’s rank correlation between 0.68 and 0.75), the regression relationship between the IgG and neutralizing antibody levels depended on the time since receipt of the second vaccine dose. Six months after receipt of the second dose, neutralizing antibody titers were substantially lower among men than among women (ratio of means, 0.64; 95% confidence interval [CI], 0.55 to 0.75), lower among persons 65 years of age or older than among those 18 to less than 45 years of age (ratio of means, 0.58; 95% CI, 0.48 to 0.70), and lower among participants with immunosuppression than among those without immunosuppression (ratio of means, 0.30; 95% CI, 0.20 to 0.46).

CONCLUSIONS

Six months after receipt of the second dose of the BNT162b2 vaccine, humoral response was substantially decreased, especially among men, among persons 65 years of age or older, and among persons with immunosuppression.

Published in NEJM (Oct. 6, 2021):

https://doi.org/10.1056/NEJMoa2114583 

BACKGROUND

On July 30, 2021, the administration of a third (booster) dose of the BNT162b2 messenger RNA vaccine (Pfizer–BioNTech) was approved in Israel for persons who were 60 years of age or older and who had received a second dose of vaccine at least 5 months earlier. Data are needed regarding the effect of the booster dose on the rate of confirmed coronavirus 2019 disease (Covid-19) and the rate of severe illness.

METHODS

We extracted data for the period from July 30 through August 31, 2021, from the Israeli Ministry of Health database regarding 1,137,804 persons who were 60 years of age or older and had been fully vaccinated (i.e., had received two doses of BNT162b2) at least 5 months earlier. In the primary analysis, we compared the rate of confirmed Covid-19 and the rate of severe illness between those who had received a booster injection at least 12 days earlier (booster group) and those who had not received a booster injection (nonbooster group). In a secondary analysis, we evaluated the rate of infection 4 to 6 days after the booster dose as compared with the rate at least 12 days after the booster. In all the analyses, we used Poisson regression after adjusting for possible confounding factors.

RESULTS

At least 12 days after the booster dose, the rate of confirmed infection was lower in the booster group than in the nonbooster group by a factor of 11.3 (95% confidence interval [CI], 10.4 to 12.3); the rate of severe illness was lower by a factor of 19.5 (95% CI, 12.9 to 29.5). In a secondary analysis, the rate of confirmed infection at least 12 days after vaccination was lower than the rate after 4 to 6 days by a factor of 5.4 (95% CI, 4.8 to 6.1).

CONCLUSIONS

In this study involving participants who were 60 years of age or older and had received two doses of the BNT162b2 vaccine at least 5 months earlier, we found that the rates of confirmed Covid-19 and severe illness were substantially lower among those who received a booster (third) dose of the BNT162b2 vaccine.

Published in New England J. Medicine (Sept. 15, 2021):

https://doi.org/10.1056/NEJMoa2114255

Israelis who had an infection were more protected against the Delta coronavirus variant than those who had an already highly effective COVID-19 vaccine. The natural immune protection that develops after a SARS-CoV-2 infection offers considerably more of a shield against the Delta variant of the pandemic coronavirus than two doses of the Pfizer-BioNTech vaccine, according to a large Israeli study that some scientists wish came with a “Don’t try this at home” label. The newly released data show people who once had a SARS-CoV-2 infection were much less likely than vaccinated people to get Delta, develop symptoms from it, or become hospitalized with serious COVID-19.  The study demonstrates the power of the human immune system, but infectious disease experts emphasized that this vaccine and others for COVID-19 nonetheless remain highly protective against severe disease and death. And they caution that intentional infection among unvaccinated people would be extremely risky. “What we don’t want people to say is: ‘All right, I should go out and get infected, I should have an infection party.’” says Michel Nussenzweig, an immunologist at Rockefeller University who researches the immune response to SARS-CoV-2 and was not involved in the study. “Because somebody could die.” The researchers also found that people who had SARS-CoV-2 previously and then received one dose of the Pfizer-BioNTech messenger RNA (mRNA) vaccine were more highly protected against reinfection than those who once had the virus and were still unvaccinated. The study, conducted in one of the most highly COVID-19–vaccinated countries in the world, examined medical records of tens of thousands of Israelis, charting their infections, symptoms, and hospitalizations between 1 June and 14 August, when the Delta variant predominated in Israel. It’s the largest real-world observational study so far to compare natural and vaccine-induced immunity to SARS-CoV-2, according to its leaders.

The research impresses Nussenzweig and other scientists who have reviewed a preprint of the results, posted yesterday on medRxiv. “It’s a textbook example of how natural immunity is really better than vaccination,” says Charlotte Thålin, a physician and immunology researcher at Danderyd Hospital and the Karolinska Institute who studies the immune responses to SARS-CoV-2 . “To my knowledge, it’s the first time [this] has really been shown in the context of COVID-19.” Still, Thålin and other researchers stress that deliberate infection among unvaccinated people would put them at significant risk of severe disease and death, or the lingering, significant symptoms of what has been dubbed Long Covid. The study shows the benefits of natural immunity, but “doesn’t take into account what this virus does to the body to get to that point,” says Marion Pepper, an immunologist at the University of Washington, Seattle. COVID-19 has already killed more than 4 million people worldwide and there are concerns that Delta and other SARS-CoV-2 variants are deadlier than the original virus. The new analysis relies on the database of Maccabi Healthcare Services, which enrolls about 2.5 million Israelis. The study, led by Tal Patalon and Sivan Gazit at KSM, the system’s research and innovation arm, found in two analyses that people who were vaccinated in January and February were, in June, July, and the first half of August, six to 13 times more likely to get infected than unvaccinated people who were previously infected with the coronavirus. In one analysis, comparing more than 32,000 people in the health system, the risk of developing symptomatic COVID-19 was 27 times higher among the vaccinated, and the risk of hospitalization eight times higher. “The differences are huge,” says Thålin, although she cautions that the numbers for infections and other events analyzed for the comparisons were “small.” For instance, the higher hospitalization rate in the 32,000-person analysis was based on just eight hospitalizations in a vaccinated group and one in a previously infected group. And the 13-fold increased risk of infection in the same analysis was based on just 238 infections in the vaccinated population, less than 1.5% of the more than 16,000 people, versus 19 reinfections among a similar number of people who once had SARS-CoV-2. No one in the study who got a new SARS-CoV-2 infection died—which prevented a comparison of death rates but is a clear sign that vaccines still offer a formidable shield against serious disease, even if not as good as natural immunity. Moreover, natural immunity is far from perfect. Although reinfections with SARS-CoV-2 are rare, and often asymptomatic or mild, they can be severe.

In another analysis, the researchers compared more than 14,000 people who had a confirmed SARS-CoV-2 infection and were still unvaccinated with an equivalent number of previously infected people who subsequently received one dose of the Pfizer-BioNTech vaccine. (In Israel, it’s recommended that people who have been previously infected get just one dose.) The team found that the unvaccinated group was twice as likely to be reinfected as the singly vaccinated. “We continue to underestimate the importance of natural infection immunity … especially when [infection] is recent,” says Eric Topol, a physician-scientist at Scripps Research. “And when you bolster that with one dose of vaccine, you take it to levels you can’t possibly match with any vaccine in the world right now.” Nussenzweig says the results in previously infected, vaccinated people confirm laboratory findings from a series of papers in Nature and Immunity by his group, his Rockefeller University colleague Paul Bieniasz and others—and from a preprint posted this month by Bieniasz and his team. They show, Nussenzweig says, that the immune systems of people who develop natural immunity to SARS-CoV-2 and then get vaccinated produce exceptionally broad and potent antibodies against the coronavirus. The preprint, for example, reported that people who were previously infected and then vaccinated with an mRNA vaccine had antibodies in their blood that neutralized the infectivity of another virus, harmless to humans, that was engineered to express a version of the coronavirus spike protein that contains 20 concerning mutations. Sera from vaccinated and naturally infected people could not do so. As for the Israel medical records study, Topol and others point out several limitations, such as the inherent weakness of a retrospective analysis compared with a prospective study that regularly tests all participants as it tracks new infections, symptomatic infections, hospitalizations, and deaths going forward in time. “It will be important to see these findings replicated or refuted,” says Natalie Dean, a biostatistician at Emory University. She adds: “The biggest limitation in the study is that testing [for SARS-CoV-2 infection] is still a voluntary thing—it’s not part of the study design.” That means, she says, that comparisons could be confounded if, for example, previously infected people who developed mild symptoms were less likely to get tested than vaccinated people, perhaps because they think they are immune. Nussenzweig’s group has published data showing people who recover from a SARS-CoV-2 infection continue to develop increasing numbers and types of coronavirus-targeting antibodies for up to 1 year. By contrast, he says, twice-vaccinated people stop seeing increases “in the potency or breadth of the overall memory antibody compartment” a few months after their second dose. For many infectious diseases, naturally acquired immunity is known to be more powerful than vaccine-induced immunity and it often lasts a lifetime. Other coronaviruses that cause the serious human diseases severe acute respiratory syndrome and Middle East respiratory syndrome trigger robust and persistent immune responses. At the same time, several other human coronaviruses, which usually cause little more than colds, are known to reinfect people regularly.

Study Cited Available in medRxiv (August 25, 2021):

https://doi.org/10.1101/2021.08.24.21262415 

Less than a month into a COVID-19 vaccine booster drive, Israel is seeing signs of an impact on the country's high infection and severe illness rates fuelled by the fast-spreading Delta variant, officials and scientists say. Delta hit Israel in June, just as the country began to reap the benefits of one of the world's fastest vaccine roll-outs. With an open economy and most curbs scrapped, Israel went from single-digit daily infections and zero deaths to around 7,500 daily cases last week, 600 people hospitalized in serious condition and more than 150 people dying in that week alone. On July 30, it began administering a third dose of the Pfizer (PFE.N)/BioNtech (22UAy.DE) vaccine to people over 60, the first country to do so. On Thursday it expanded eligibility to 30-year-olds and up whose second dose was given at least 5 months prior, saying the age may drop further.  In the past 10 days, the pandemic is abating among the first age group, more than a million of whom have received a third vaccine dose, according to Israeli health ministry data and scientists interviewed by Reuters. The rate of disease spread among vaccinated people age 60 and over - known as the reproduction rate - began falling steadily around Aug. 13 and has dipped below 1, indicating that each infected person is transmitting the virus to fewer than one other person. A reproduction rate of less than 1 means an outbreak is subsiding. https://tmsnrt.rs/3grj7kv Scientists said booster shots are having an impact on infections, but other factors are likely contributing to the decline as well.  "The numbers are still very high but what has changed is that the very high increase in the rate of infections and severe cases has diminished, as has the pace at which the pandemic is spreading," said Eran Segal, data scientist at the Weizmann Institute of Science and an adviser to the government. "This is likely due to the third booster shots, an uptake in people taking the first dose and the high number of people infected per week, possibly up to 100,000, who now have natural immunity," Segal said. 

BOOSTER VS LOCKDOWN

After reaching one of the highest per-capita infection rates in the world this month, the question now is whether Israel can battle its way out of a fourth outbreak without imposing another lockdown that would damage its economy.  Evidence has emerged showing that while the vaccine is still highly effective in preventing serious illness, its protection diminishes with time. But there is no consensus among scientists and agencies that a third dose is necessary, and the World Health Organization has said more of the world should be vaccinated with a first dose before people receive a third dose. read more The United States has announced plans to offer booster doses to all Americans, eight months after their second vaccine dose, citing data showing diminishing protection. Canada, France and Germany have also planned booster campaigns. About a million of Israel's 9.3 million population have so far chosen not to vaccinate at all and children under 12 are still not eligible for the shots. On Thursday, health officials said they have identified waning immunity among people under 40, although relatively few have fallen seriously ill. read more 

According to Doron Gazit, a member of the Hebrew University's COVID-19 expert team which advises government, the rise in cases of severely ill vaccinated people in the 60 and older group has been steadily slowing to a halt in the last 10 days. "We attribute this to the booster shots and to more cautious behaviour recently," Gazit said.  More than half of those over 60 have received a third jab, according to the Health ministry. The rate of new severe cases among unvaccinated patients 70 and older is now seven times that of vaccinated patients, and the gap will continue to grow as long as infections rise, according to Gazit. Among those over 50, that gap is four-fold. "We are optimistic, but very cautious," Israeli Health Minister Nitzan Horowitz told public broadcaster Kan on Sunday. "It gives us more time, slows the spread and we're moving away from lockdown." But even if the boosters are slowing the pandemic's pace, it is unlikely to fend Delta off entirely. Dvir Aran, biomedical data scientist at Technion - Israel's Institute of Technology, said that while cases are retreating, other measures are needed alongside boosters to stop the pandemic. "It will take a long time until enough people get a third dose and until then thousands more people will getting seriously ill." Since Delta's surge, Israel has reimposed indoor mask wearing, limitations on gatherings and ramped up rapid testing. Its "living with COVID" policy will be tested come September, when schools reopen after summer break and when the Jewish holiday season starts, with families traditionally gathering to celebrate.

The short-term effectiveness of a two-dose regimen of the BioNTech/Pfizer mRNA BNT162b2 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccine was widely demonstrated. However, long term effectiveness is still unknown. A nationwide vaccination campaign was initiated early in Israel, allowing for a real-world evaluation of the interaction between protection and time-from-vaccine. The Delta (B.1.617.2) variant became the dominant strain in Israel in June 2021, as Israel is currently experiencing a new surge of cases. Leveraging the centralized computerized database of Maccabi Healthcare Services (MHS), we assessed the correlation between time-from-vaccine and incidence of breakthrough infection. We found that the risk for infection was significantly higher for early vaccinees compared to those vaccinated later. This preliminary finding should prompt further investigagions into long-term protection against different strains, and prospective clinical trials to examine the effect of a booster vaccine against breakthrough infection.

Available as preprint in medRxiv (July 31, 2021):

https://doi.org/10.1101/2021.07.29.21261317 

The BNT162b2 mRNA vaccine is highly effective against SARS-CoV-2. However, apprehension exists that variants of concern (VOCs) may evade vaccine protection, due to evidence of reduced neutralization of the VOCs B.1.1.7 and B.1.351 by vaccine sera in laboratory assays. We performed a matched cohort study to examine the distribution of VOCs in infections of BNT162b2 mRNA vaccinees from Clalit Health Services (Israel) using viral genomic sequencing, and hypothesized that if vaccine effectiveness against a VOC is reduced, its proportion among breakthrough cases would be higher than in unvaccinated controls.

Analyzing 813 viral genome sequences from nasopharyngeal swabs, we showed that vaccinees who tested positive at least 7 days after the second dose were disproportionally infected with B.1.351, compared with controls. Those who tested positive between 2 weeks after the first dose and 6 days after the second dose were disproportionally infected by B.1.1.7. These findings suggest reduced vaccine effectiveness against both VOCs within particular time windows. Our results emphasize the importance of rigorously tracking viral variants, and of increasing vaccination to prevent the spread of VOCs. At early time points after vaccination with a single dose or two doses of the BNT162b2 mRNA COVID-19 vaccine, breakthrough SARS-CoV-2 infections can be disproportionately caused by the B.1.1.7 or B.1.351 variants of concern, underlining the need to ensure rapid and complete vaccination.

Published in Nature Medicine (June 14, 2021):

https://doi.org/10.1038/s41591-021-01413-7

The coronavirus variant discovered in South Africa can "break through" Pfizer/BioNTech's COVID-19 vaccine to some extent, a real-world data study in Israel found, though its prevalence in the country is low and the research has not been peer reviewed.  The study, released on Saturday, compared almost 400 people who had tested positive for COVID-19, 14 days or more after they received one or two doses of the vaccine, against the same number of unvaccinated patients with the disease. It matched age and gender, among other characteristics. The South African variant, B.1.351, was found to make up about 1% of all the COVID-19 cases across all the people studied, according to the study by Tel Aviv University and Israel’s largest healthcare provider, Clalit. But among patients who had received two doses of the vaccine, the variant’s prevalence rate was eight times higher than those unvaccinated - 5.4% versus 0.7%.  This suggests the vaccine is less effective against the South African variant, compared with the original coronavirus and a variant first identified in Britain that has come to comprise nearly all COVID-19 cases in Israel, the researchers said. “We found a disproportionately higher rate of the South African variant among people vaccinated with a second dose, compared to the unvaccinated group. This means that the South African variant is able, to some extent, to break through the vaccine’s protection,” said Tel Aviv University’s Adi Stern.

The researchers cautioned, though, that the study only had a small sample size of people infected with the South African variant because of its rarity in Israel. They also said the research was not intended to deduce overall vaccine effectiveness against any variant, since it only looked at people who had already tested positive for COVID-19, not at overall infection rates. Pfizer and BioNTech could not be immediately reached for comment outside business hours. The companies said on April 1 that their vaccine was around 91% effective at preventing COVID-19, citing updated trial data that included participants inoculated for up to six months. In respect to the South African variant, they said that among a group of 800 study volunteers in South Africa, where B.1.351 is widespread, there were nine cases of COVID-19, all of which occurred among participants who got the placebo. Of those nine cases, six were among individuals infected with the South African variant.

Some previous studies have indicated that the Pfizer/BioNTech shot was less potent against the B.1.351 variant than against other variants of the coronavirus, but still offered a robust defence.

While the results of the study may cause concern, the low prevalence of the South African strain was encouraging, according to Stern. “Even if the South African variant does break through the vaccine’s protection, it has not spread widely through the population,” said Stern, adding that the British variant may be “blocking” the spread of the South African strain. Almost 53% of Israel’s 9.3 million population has received both Pfizer doses. Israel has largely reopened its economy in recent weeks while the pandemic appears to be receding, with infection rates, severe illness and hospitalizations dropping sharply. About a third of Israelis are below the age of 16, which means they are still not eligible for the shot.

Findings available in medRxiv (April 9, 2021):

https://doi.org/10.1101/2021.04.06.21254882 

The researchers said the findings support policies delaying the second shot in efforts to stretch supplies and speed up immunizations.