2023-06-27 20:03:20
COVID-19 outbreak following a party office in Laval, a karaoke evening in Quebec or a wedding in Montreal… The cases of massive contamination that made the headlines during the pandemic – sometimes called superspreader events – have enabled scientists to identify several factors facilitating the community spread of SARS -CoV-2, such as the lack of ventilation, the many social contacts or the physical proximity of individuals.
However, scientists are still racking their brains to explain the phenomenon of super-contaminating individuals, those people who eject far more infectious virus particles into the air than the average individual.
In South Korea, for example, one of the first two confirmed cases of COVID-19 in 2020 had attended two rallies during which he allegedly infected more than 1,000 people. The results of a British study recently published in The Lancet Microbe provide some answers… although the ethics of the research protocol is not unanimous.
Deliberately infected volunteers
In 2021, 36 healthy people not yet vaccinated once morest COVID-19 were knowingly infected with SARS-CoV-2, placed in individual rooms and followed for at least 14 days by a team of researchers from Imperial College. from London. Their goal? Monitoring environment, time of infection, amount and strain of virus to assess whether individual factors, such as physiology or genetics, may play a role in a person’s ability to transmit the coronavirus.
This was the first time during the pandemic that this type of clinical trial, called a “challenge study”, had been used, which generated a some controversy. “Ethically, it’s quite surprising that the protocol was accepted! It is still a virus that can cause serious illnesses. I don’t think our university would be so open to that, says Benoit Barbeau, professor in the Department of Biological Sciences at the University of Quebec in Montreal and expert in virology. It should be noted, however, that an ethics committee looks heavily at the criteria for participation in a study before accepting it. You will notice that the volunteers are between 18 and 30 years old, so they are young and in good health… None have developed serious symptoms, by the way. And the results of the study are surprising!”
Asymptomatic supercontaminators
Among these “surprising results”: two individuals projected into the air 86% of all the virus particles detected during the study. “The study thus demonstrates the existence of the famous supershedders [supercontaminateurs], emphasizes Benoit Barbeau. We did not have such concrete data on this subject. Further studies will now be needed to better understand who they are. »
Additionally, of the 18 effectively infected volunteers, “the people who reported the most severe symptoms were not the ones who shed the most virus,” note the study authors.
An infected, but asymptomatic person also emitted large amounts of virus. “It demonstrates how asymptomatic people can play an important role in the pandemic. Not only do they carry the virus, but they can even spread infinitely more infectious particles through the air than a person showing symptoms. Even if the sample of participants is small, this is very useful data! “, emphasizes Benoit Barbeau.
The test also provides information on how infectiousness progresses over time. Thus, less than 10% of the viral particles were emitted into the air during the incubation period, that is to say before the infected volunteers tested positive for an antigenic test, also called a rapid test. “It demonstrates the usefulness of these tests, as there are virtually no particles emitted before participants test positive for antigen tests. Isolation from a positive result was therefore an effective measure, ”underlines Benoit Barbeau.
Among other public health measures shown to be effective, a recent American study shows that wearing a mask reduced the risk of infection by 64.2% during the Omicron wave, while vaccination reduced transmission by 40.7% during the Delta wave and 31% during the Omicron wave .
New trials in sight
The British team plans to carry out further studies of deliberate infection, this time with newer variants of the coronavirus. Fortunately, in the event of severe symptoms, volunteers will now be able to benefit from the new treatments developed once morest COVID-19.
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