Virus World

A new analysis published in The Lancet Microbe shows how the SARS-CoV-2 virus spreads from the nose to the air and surfaces in the immediate surroundings. The findings are the second batch of results to come from the COVID-19 Human Challenge Program, led by Imperial College London and partners, and provide granular insights into how people infected with SARS-CoV-2 spread the virus to their immediate surroundings. In February 2021, 36 healthy, young participants with no previous immunity to the virus were infected with SARS-CoV-2 under controlled clinical conditions in a residential facility at the Royal Free Hospital in London, where they could be carefully monitored. They remained at the facility until they were no longer infectious. The facility enabled researchers to track the course of infection in great detail, with the clinical team taking daily swabs from participants' noses and mouths, as well as environmental samples of the air and swabs of surfaces in their rooms.

Viral emissions

Out of 36 initial participants, a total of 18 became infected. Analysis showed that two individuals emitted substantially more virus into the air than the other infected participants, but displayed no significantly worse symptoms. The researchers suggest this may represent the small proportion of individuals who have potential to be highly infectious, sometimes described as "superspreading." Analysis found large amounts of viral RNA in air samples, in exhaled breath, as well as swabs of participants hands and on surrounding surfaces, including frequently touched surfaces such as door handles and TV remote controls, showing how an infected person contaminates their surrounding environment and can spread the virus. Viral emissions correlated strongly with the level of virus detected in people's noses, more than in their throat, highlighting the nose as a significant route for infected people shedding virus into the air and environment. According to the researchers, the latest analysis further highlights the routes by which the virus is transmitted from person to person—directly into the air, depositing onto nearby surfaces, and transferred from contaminated hands to frequently touched surfaces, such as door handles and remote controls.

Reliable indicators

They also show that positive lateral flow tests and visible symptoms were reliable indicators of when people were infectious and emitting virus into the air and environment. The vast majority of virus was emitted after people noticed their first symptoms, with very little virus released into the environment before that (pre-symptomatically). They found no significant link between the severity of participants' symptoms and the amount of virus they shed into the environment. According to the researchers, the findings highlight the need to reinforce public health messaging around proper face mask use, hand washing and surface cleaning, as well as how human challenge studies continue to add to our knowledge of COVID-19 infection and transmission. Dr. Anika Singanayagam, NIHR Academic Clinical Lecturer in the Department of Infectious Disease at Imperial College London, and joint first author of the study, said, "Our latest findings add to the existing body of knowledge on COVID-19 transmission. By studying infection in a controlled environment, we can collect unique, detailed measurements of virus emitted that allow us to understand how and when people with COVID-19 are contagious to others. These types of measurements are challenging to collect in real-world studies. "Our data indicate that much of the virus people shed comes from the nose, further highlighting the importance of face masks covering the nose as well as the mouth when they're used. But it also shows how virus can be transferred from hands to contaminate surfaces, like door handles or remote controls, which become a source of infection."

Dr. Jay, Jie Zhou, research associate in the Department of Infectious Disease at Imperial College London, and joint first author of the study, said, "Understanding when infected people are contagious and how to detect when they are contagious is important—it can help us to use interventions like face masks or social distancing more effectively. The data in our study highlights that being aware of, and acting on, the first minor symptoms that signal an infection, coupled with frequent self-testing with lateral flow tests, can effectively reduce onward spread." Professor Wendy Barclay, head of the Department of Infectious Disease at Imperial College London, said, "One of the most important things we need to know for controlling the spread of respiratory viruses, such as SARS-CoV-2, is when are people who are actively infected with the virus most likely to infect others? That information can help to tell us how the virus will spread, and how best to use interventions to stop the outbreak. "Human challenge studies enable us to gain granular insights into the infection which we might not otherwise be able to. They play an important role in our understanding of infectious diseases, and should be considered a part of future pandemic preparedness."

Previous findings

The latest findings add to several key clinical insights already gained from the COVID-19 Human Challenge Program, published in February 2022. These include that symptoms start to develop on average two days after contact with the virus, that infection first appears in the throat, infectious virus peaks about five days into infection and, at that stage, is significantly more abundant in the nose than the throat. The first analysis also found that lateral flow tests (LFTs) are a reassuringly reliable indicator of whether infectious virus is present in the nose and throat (i.e., whether they are a likely to be infectious to other people).

Original research published (June 9, 2023) at The Lancet Microbe:

https://doi.org/10.1016/S2666-5247(23)00101-5 

Researchers hope to learn things about how the immune system responds to the coronavirus that would be impossible outside a lab.  In the coming weeks, a small, carefully selected group of volunteers is expected to arrive on the 11th floor of a London hospital to be given what the rest of the world’s 7.8 billion people have been trying to avoid: a coronavirus infection. They will be administered tiny droplets of the virus into their nostrils as part of a plan authorized by British regulators on Wednesday to deliberately infect unvaccinated volunteers with the coronavirus. The scientists hope to eventually expose vaccinated people to the virus as a way of comparing the effectiveness of different vaccines. But before that, the project’s backers have to expose unvaccinated volunteers in order to determine the lowest dose of the virus that will reliably infect them. By controlling the amount of the virus people are subjected to and monitoring them from the moment they are infected, scientists hope to discover things about how the immune system responds to the coronavirus that would be impossible outside a lab — and to develop ways of directly comparing the efficacy of treatments and vaccines. “We are going to learn an awful lot about the immunology of the virus,” Peter Openshaw, an Imperial College London professor involved in the study, said on Wednesday. He added that the study would be able “to accelerate not only understanding of diseases caused by infection, but also to accelerate the discovery of new treatments and of vaccines.”

Study that infected young adults with the coronavirus finds virus may largely be shed from nose

A small trial that involved deliberately infecting volunteers with the virus that causes covid-19 has revealed new details on how it can cause mild to moderate symptoms.  This type of research is known as a human challenge trial, and while similar studies have been conducted for various viruses over the years, this is the first to report findings on the coronavirus. Researchers in the UK gave 36 volunteers aged between 18 and 29 a low dose of the virus via droplets placed in the nose. The virus was taken from a person who became ill with covid-19 very early in the pandemic, before any notable variants had emerged.  Eighteen of the volunteers became infected with the virus, and 16 of them developed cold-like symptoms, such as a runny rose, sore throat, cough, fever or headache. Many of these symptoms were not included on symptom lists published by health authorities early in the pandemic. Thirteen of the volunteers also temporarily lost their sense of taste and smell.  Among those who became infected, the virus could be detected, and symptoms began to develop, within 42 hours. This incubation period is significantly shorter than estimates at the time, which put the incubation period between two and 14 days.

The virus could be detected in the throat at 40 hours, before it could be detected in the nose at around 58 hours. Peak levels of the virus were found to be higher in the nose, suggesting that more virus may spread this way – and highlighting the importance of ensuring face coverings shield the nose as well as the mouth. Other findings from the study support the use of lateral flow tests in picking up infectious cases of the disease. “We found that overall, lateral flow tests correlate very well with the presence of infectious virus,” Christopher Chiu at Imperial College London, the trial’s chief investigator, said in a statement. “Even though in the first day or two they may be less sensitive, if you use them correctly and repeatedly, and act on them if they read positive, this will have a major impact on interrupting viral spread.” None of the volunteers developed any serious symptoms and no damage was seen in their lungs.