Last week, again, local Chinese authorities reported a relapse of Covid-19. For several months, alerts have been regularly launched, often denied. Thus, in May, the case of some nearly 300 South Koreans test positive after being ill for the first time denied. After additional investigations, it appeared that the virological tests had indeed detected the residual presence of genes of the virus, but the virus was no longer active. Where are we today? Marc Eloit, head of the “Discovery of pathogens” laboratory at the Institut Pasteur, answers.
To your knowledge, can people be re-infected with SARS CoV2 ?
From time to time we hear of people who appear to have been re-infected, but the information is very patchy. It is not known if this is a false positive, persistent infection, or reinfection. So far, there have not been any fully documented, proven cases. It’s reassuring.
How do you study the risks of reinfection?
We will learn a lot from the ongoing experiments in vaccine trials, especially in animals, because we can see which ones are protected after experimental infection. We are also monitoring populations that have been heavily infected, such as caregivers, to find out whether certain people will reinfect themselves and analyze the results based on their previous immune response.
What do we know about the immune response generated by infection with the SARS-Cov2 virus (responsible for the Covid-19 disease)?
There is now a lot of information about the body’s response after infection. The kinetics of antibody production and the proportion of neutralizing antibodies are known. What we do not know are the correlates of protection: what protects and for how long?
A priori, the infection should protect?
The general rule in virology is that when you have had a viral disease, you do not get reinfected for a while. But that doesn’t say anything about the duration of immunity, or what happens with the many people who get infected without getting sick. What can happen is that the minor forms cause low level, low duration immunity. And that serious systemic infections induce longer lasting immunity.
Does conferred immunity seem short, according to several studies?
According to publications, the presence of post-infectious antibodies, generally very important in protection, seems short. So if there is protection in the following months, it will not extend for very long. The other three or four seasonal coronaviruses that circulate (and cause colds) are known to not protect against SARS-Cov2. And even if there is a significant prevalence of antibodies in the population, they circulate every year.
Does this invalidate the hope of a truly protective vaccine?
It is possible that the future vaccine will require annual boosters on the influenza model, but for slightly different reasons (the influenza virus varies each year and requires adaptations). By choosing a time of seasonal prephase, if the circulation of the virus becomes seasonal.
Researchers have hypothesized that the severe form of Covid-19 is linked to facilitating antibodies? Can you explain what it is?
These are non-neutralizing antibodies (which do not neutralize the infection by the virus), which bind to a domain other than that necessary to neutralize it, or which are in too low a proportion. They can then facilitate the entry of the virus into immune cells such as macrophages and can stimulate an exacerbated immune response. Either they can facilitate infection, or they can facilitate an excessive or deviated immune response. Developments in vaccines must take this risk into account. This is undoubtedly the mechanism that stopped the dengue vaccine developed by Sanofi.
Have any facilitating antibodies been detected for Covid-19?
They exist for other viruses, including other coronaviruses. In particular on experimental models for SARS (the close cousin of SARS-CoV2).
Is this the research you’re doing in your lab?
We are working on antibodies, correlates of protection, the role of antibodies against the virus and against seasonal coronaviruses in facilitation or protection.
In our last paper, We have shown in collaboration with our hospital colleagues, in particular from Necker, that infection with seasonal coronaviruses does not protect children against infection with SARS Cov2 or the rare severe inflammatory form, Kawasaki syndrome.