Virus World

New evidence suggests that people who have had COVID-19 may be immune to SARS-CoV-2, the virus that causes it, for at least 5–7 months, if not longer. Recent alleged cases of reinfection with SARS-CoV-2, the coronavirus that causes COVID-19, have raised concerns that the human immune system may only provide short-term protection against the virus. In addition, scarce research has suggested that the number of antibodies in a person’s bloodstream that is capable of disabling the virus declines sharply after an initial infection. However, scientists at the University of Arizona (UArizona) College of Medicine in Tucson have now found evidence of long lasting immunity in people who have had COVID-19. 

They tested for the presence of antibodies to the virus in nearly 6,000 individuals and then followed them up for several months. “We clearly see high quality antibodies still being produced 5–7 months after SARS-CoV-2 infection,” says Dr. Deepta Bhattacharya, an associate professor of immunobiology at the university, who co-led the research.  “Many concerns have been expressed about immunity against COVID-19 not lasting. We used this study to investigate that question and found immunity is stable for at least 5 months.”  Bhattacharya points out that people who contracted the SARS-CoV virus responsible for the 2002–2004 outbreak of SARS were still immune 12–17 years after infection. This virus is very similar to SARS-CoV-2.  “If SARS-CoV-2 is anything like the first one, we expect antibodies to last at least 2 years, and it would be unlikely for anything much shorter,” he says.  In their paper, published in the journal Immunity, the scientists also note that out of nearly 30 million cases of COVID-19 since December 2019, there have been only about 10 confirmed cases of reinfection...

Study published in Immunity (Oct. 13, 2020):

https://doi.org/10.1016/j.immuni.2020.10.004

Antibodies to the virus faded quickly in asymptomatic people, scientists reported. That does not mean immunity disappears. It’s a question that has haunted scientists since the pandemic began: Does everyone infected with the virus produce antibodies — and if so, how long do they last? Not very long, suggests a new study published Thursday in Nature Medicine. Antibodies — protective proteins made in response to an infection — may last only two to three months, especially in people who never showed symptoms while they were infected.

The conclusion does not necessarily mean that these people can be infected a second time, several experts cautioned. Even low levels of powerful neutralizing antibodies may still be protective, as are the immune system’s T cells and B cells. But the results offer a strong note of caution against the idea of “immunity certificates” for people who have recovered from the illness, the authors suggested. Antibodies to other coronaviruses, including those that cause SARS and MERS, are thought to last about a year. Scientists had hoped that antibodies to the new virus might last at least as long. Several studies have now shown that most people who are visibly ill with Covid-19 develop antibodies to the virus, although it has been unclear how long those antibodies last. The new study is the first to characterize the immune response in asymptomatic people. The researchers compared 37 asymptomatic people to an equal number who had symptoms in the Wanzhou District of China. The investigators found that asymptomatic people mount a weaker response to the virus than those who develop symptoms. Antibody levels fell to undetectable levels in 40 percent of asymptomatic people, compared with just 13 percent of symptomatic people.

The sample size is small, however, and the researchers did not take into account protection offered by immune cells that may fight the virus on their own or make new antibodies when the virus invades. A few studies have shown that the coronavirus stimulates a robust and protective cellular immune response....

Original Study available in Nature Medicine (June 18, 2020):

https://doi.org/10.1038/s41591-020-0965-6