Coronavirus recovery may not confer immunity, experts warn


Even though virologists focus on the virus that causes COVID-19, a very basic question remains unanswered: are those recovering from the disease immune?

There is no clear answer to this question, experts say, although many have speculated that contracting the life-threatening disease confers immunity, at least for a while.

“Being immunized means that you have developed an immune response against a virus such that you can repel it,” said Eric Vivier, professor of immunology at the Marseille public hospital.

“Our immune systems remember, which normally prevents you from being infected with the same virus later. “

For some viral diseases like measles, defeating the disease provides lifelong immunity.

But for RNA-based viruses such as Sars-Cov-2 – the scientific name for the bug that causes COVID-19 disease – it takes about three weeks to build a sufficient amount of antibodies, and even then, they can provide protection for only a few months, Vivier told AFP.

At least that’s the theory. In reality, the new coronavirus has surprised one after the other, to the point where virologists and epidemiologists are very little sure.

“We don’t have the answers to that – it’s an unknown,” said Michael Ryan, executive director of the World Health Organization’s emergency program at a press conference this week, when he was asked how long a cured COVID-19 patient would have immunity.

“We would expect it to be a reasonable protection period, but it is very difficult to say with a new virus – we can only extrapolate from other coronaviruses, and even these data are quite limited. “

For SARS, which killed around 800 people worldwide in 2002 and 2003, the recovered patients remained protected “for about three years on average”, explained to AFP François Balloux, director of the Genetics Institute of the University College of London.

“We can certainly be reinfected, but after how long? We will only know this retroactively. “

Read also: The excessive reaction of the immune system which can be fatal

False negatives

A recent non-peer-reviewed study from China reported rhesus monkeys that recovered from Sars-Cov-2 and were not reinfected when they were again exposed to the virus.

“But that really doesn’t reveal anything,” said Frédéric Tangy, a researcher at the Institut Pasteur, noting that the experiment only took place over a month.

Indeed, several cases from South Korea – one of the first countries affected by the new coronavirus – have revealed that patients who recovered from COVID-19 were subsequently tested positive for the virus.

But there are several ways to explain this result, the scientists warned.

Although it is not impossible that these people will be infected a second time, there is little evidence that this is the case.

More likely, said Balloux, is that the virus has never completely gone in the first place and remains – dormant and asymptomatic – as a “chronic infection”, like herpes.

As the tests for live virus and antibodies have not yet been perfected, it is also possible that these patients have at one point tested a “false negative” when in fact they had not got rid of the pathogen .

“This suggests that people remain infected for a long time – several weeks,” added Balloux. “It is not ideal. “

Another pre-publication study that examined 175 patients recovered from Shanghai showed different concentrations of protective antibodies 10 to 15 days after the onset of symptoms.

“But whether this antibody response actually means immunity is a separate issue,” said Maria Van Kerhove, technical manager of the WHO emergency program.

“This is something that we really need to understand better – what this antibody response looks like in terms of immunity. “

Indeed, a multitude of questions remain.

“We are wondering if someone who has overcome COVID-19 is really as protected,” said Jean-François Delfraissy, president of the official scientific council of France.

Read also: Why are some S. Koreans who have recovered from the coronavirus test positive again?

Immunity passports

For Tangy, an even darker reality cannot be excluded.

“It is possible that the antibodies someone develops against the virus may increase the risk of the disease getting worse,” he said, noting that the most severe symptoms occur later after the patient has formed. antibodies.

At the moment, we also don’t know which antibodies are most effective in fighting the disease: someone who is almost dead, or someone who has only mild symptoms or even no symptoms. And does age make a difference?

Faced with all these uncertainties, some experts doubt the advisability of pursuing a strategy of “collective immunity” such that the virus – unable to find new victims – resists itself when a majority of the population is immunized.

“The only real solution at the moment is a vaccine,” Archie Clements, a professor at Curtin University in Perth, Australia, told AFP.

At the same time, laboratories are developing a multitude of antibody tests to see what proportion of the population in different countries and regions has been infected.

Such an approach has been favored in Britain and Finland, while in Germany some experts have suggested the idea of ​​an “immunity passport” which would allow people to return to work.

“It is too premature at this point,” said Saad Omer, professor of infectious diseases at the Yale School of Medicine.

“We should be able to get clearer data very quickly – in a few months – when there are reliable antibody tests with sensitivity and specificity. “

One concern is about “false positives” caused by tests for antibodies unrelated to COVID-19.

The idea of ​​passports or immunity certificates also raises ethical questions, the researchers said.

“People who absolutely need to work – to feed their families, for example – could try to get infected,” said Balloux.

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