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Even when virologists focus on the virus that causes COVID-19, a very basic question remains unanswered: Do those recovering from the disease have immunity?
Experts say there is no clear answer to this question, even if many have assumed that contracting the life-threatening disease confers immunity, at least for a time.
“Being immunized means that you have developed an immune response against a virus so you can reject it,” explained Eric Vivier, professor of immunology at the Marseille public hospital system.
“Our immune systems remember, which typically prevents you from being infected with the same virus later.”
For some viral diseases like measles, overcoming the disease confers immunity for life.
But for RNA-based viruses like Sars-Cov-2, the scientific name for the virus that causes COVID-19 disease, it takes about three weeks to generate enough antibodies, and they can still provide protection for just a few months, Vivier told AFP.
At least, that is the theory. In reality, the new coronavirus has thrown one surprise after another, to the point that virologists and epidemiologists are sure of very little.
“We don’t have the answers to that, it’s unknown,” Michael Ryan, executive director of the World Health Organization’s Emergency Program, said at a news conference this week when asked how long a recovered COVID patient would have immunity. -19.
“We would expect it to be a reasonable period of protection, but it is very difficult to say with a new virus: we can only extrapolate from other coronaviruses, and even that data is quite limited.”
For SARS, which killed about 800 people worldwide in 2002 and 2003, the recovered patients remained protected “for about three years, on average,” Francois Balloux, director of the Institute of Genetics at University College of London.
“One can certainly be reinfected, but after how long? We will only know retroactively.”
Also read: the overreaction of the immune system that can be fatal
False negatives
A recent study from China that has not gone through a peer review reported on rhesus monkeys that recovered from Sars-Cov-2 and did not re-infect when they were once again exposed to the virus.
“But that doesn’t really reveal anything,” said Pasteur Institute researcher Frederic Tangy, noting that the experiment ran for just a month.
In fact, several cases from South Korea, one of the first countries affected by the new coronavirus, found that patients who recovered from COVID-19 later tested positive for the virus.
But there are several ways to explain that result, the scientists cautioned.
While it is not impossible for these people to become infected a second time, there is little evidence that this is what happened.
Most likely, Balloux said, the virus never completely disappeared in the first place and remains, latent and asymptomatic, like a “chronic infection” like herpes.
Because the tests to detect live viruses and antibodies have not yet been perfected, it is also possible that these patients at some point had a “false negative” when, in fact, they had not been rid of the pathogen.
“That suggests that people remain infected for a long time, several weeks,” Balloux added. “That is not ideal.”
Another pre-publication study examining 175 patients recovered in Shanghai showed different concentrations of protective antibodies 10 to 15 days after the onset of symptoms.
“But whether that antibody response really means immunity is a separate question,” said Maria Van Kerhove, Technical Leader of the WHO Emergency Program.
“That’s something we really need to understand better: what that antibody response looks like in terms of immunity.”
In fact, many questions remain.
“We are at the stage of asking if someone who has passed COVID-19 is really that protected,” said Jean-Francois Delfraissy, chairman of France’s official scientific advisory board.
Also read: Why do some S. Koreans who recovered from the coronavirus test positive again?
Immunity passports
For Tangy, an even bleaker reality cannot be excluded.
“It is possible that the antibodies someone develops against the virus may actually increase the risk that the disease will worsen,” he said, noting that the more severe symptoms appear later, after the patient has formed antibodies.
At the moment, it is also unclear which antibodies are most potent in counteracting the disease: someone who almost died, or someone with mild or even no symptoms. And does age make a difference?
Faced with all these uncertainties, some experts have doubts about the wisdom of pursuing a “collective immunity” strategy so that the virus, unable to find new victims, goes away on its own when the majority of the population is immune.
“The only real solution for now is a vaccine,” Archie Clements, a professor at Curtin University in Perth Australia, told AFP.
At the same time, laboratories are developing a series of antibody tests to see what proportion of the population in different countries and regions has been contaminated.
Such an approach has been favored in Britain and Finland, while in Germany some experts have raised the idea of an “immunity passport” that would allow people to return to work.
“It is too premature at the moment,” said Saad Omer, professor of infectious diseases at Yale School of Medicine.
“We should be able to get clearer data very quickly, in a couple of months, when there will be reliable antibody tests with sensitivity and specificity.”
One concern is “false positives” caused by tests that detect antibodies unrelated to COVID-19.
The idea of passports or immunity certificates also raises ethical questions, the researchers say.
“People who absolutely need to work, to feed their families, for example, could try to get infected,” Balloux said.
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