Posted on January 31, 2021 at 5:00 a.m.
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Regular re-exposure
COVID-19 could become a less serious disease, provided it circulates abundantly. Like the common cold. This is the modeling conclusion by Jennie Lavine, a postdoctoral researcher at Emory University, Atlanta, published in early January in the journal Science. « Everything indicates SARS-CoV-2, the coronavirus responsible for COVID-19, is similar to other coronaviruses, which cause colds, says Mme Lavine. Children are almost unaffected, although they do not have prior immunity. And adults have mild illness as long as they are re-infected regularly. There is already evidence that people who are re-infected with SARS-CoV-2 have a milder form of the disease, according to Mme Lavine.
The common cold of 2003 …
One of the most compelling evidence that coronaviruses can all be serious in people without immunity came in 2003 in British Columbia. “There was an outbreak of a respiratory virus in a retirement home, where about 100 residents had significant symptoms and eight died,” explains Mme Lavine. Eventually, it turned out to be a cold coronavirus, which normally doesn’t cause as much morbidity. It is possible that these elderly people were isolated, therefore had not been recently infected with this coronavirus and were no longer protected against serious illness. The analysis of this outbreak was published in 2006 in the Canadian Journal of Infectious Disease, Medicine and Microbiology.
… and that of 2022
Cold coronaviruses could therefore be more virulent next year, when the population will be vaccinated and social contacts will resume. “It is believed that with a host of respiratory viruses, which circulate less, there will be less immunity, therefore more severe cases of the disease,” says Mme Lavine.
Lessons from SARS
Researchers have drawn lessons from the SARS epidemic, which was caused in 2003 in Hong Kong and Ontario by another coronavirus, SARS-CoV-1. “SARS was a very painful natural experience,” remarks Mme Lavine. SARS-CoV-1 disappeared because it was not contagious before the onset of severe symptoms, but it appears that the immunity it generated lasted a relatively long time. There are three main components of immunity: antibodies and B and T cells. Antibodies to SARS-CoV-1 were undetectable seven years after infection, but the latest studies of SARS survivors show that T cells still responded to SARS-CoV-1 recently. “These data are consistent with the idea that the immunity generated by coronaviruses protects against severe versions of the disease, but does not prevent transmission of the virus. ”
Duration of immunity
The first studies on the duration of immunity confirm the modeling, according to Mme Lavine. “We see that some of the components of immunity do not last long, barely two months, which allows reinfection. But other components of immunity last longer, which explains the protection against severe forms of COVID-19. ”
The vaccine conundrum
It is not yet clear whether COVID-19 vaccines limit the transmission of the disease in addition to reducing the risk of symptoms and complications. “If we cannot eradicate SARS-CoV-2, which would be very difficult anyway, the best is that the vaccine allows transmission [tout en protégeant contre les formes graves de la maladie], like the flu shot, says Mme Lavine. This would allow the virus to circulate and the population to maintain its immunity against severe forms of the disease when the protection of the vaccine is reduced. Does this mean that SARS-CoV-2 transmission should be encouraged after everyone has been vaccinated? And therefore to discourage the wearing of the mask at this time? “Once everyone has been vaccinated, yes, according to our modeling, it will be necessary to have as much circulation of SARS-CoV-2 as possible,” says Mme Lavine. I think people who are elderly or at risk of complications, such as those with heart disease and those with compromised immune systems, should wear a mask for protection, as well as those who hang out with them. But if not, in fact, we may wonder about the recommendations to wear a mask when we have symptoms. ”
The Russian flu of 1890
Another piece of the puzzle is provided by a Belgian study published in 2005 in the Journal of Virology. « Study shows that one of the four common cold coronaviruses, OC-43, appeared in the late XIXe century, although it was not identified until the 1960s, says Mme Lavine. It is therefore possible that the “Russian flu” of 1890, whose virus has never been identified, was caused by this new coronavirus, a kind of COVID-19 pandemic 130 years ago. A demographer from the University of Montreal who works a lot on historical pandemics, Alain Gagnon, considers this hypothesis “very interesting”, and says that it “certainly deserves to be explored”. But he points out that the Russian flu had a high infant mortality, unlike COVID-19, and that data shows that people born soon after 1890 were less affected by the flu pandemic of 1968, presumably because it It was the same influenza strain, H3, as the “Russian flu”. Several studies show that exposure during childhood and adolescence to a new influenza strain subsequently protects against this same influenza strain, until old age.
IMAGE FROM THE NATIONAL LIBRARY OF MEDICINE WEBSITE
The Russian flu of 1889-1890 in Paris
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Coronaviruses in figures
20% to 30% of colds are caused by four coronaviruses.
Source: Emory University
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