Coronavirus: four questions on the cases of reinfection identified so far

DECRYPTION

It is now a certainty: you can catch Covid-19 twice, and even be sicker the second time than the first.

These cases of reinfection are still very rare but raise many questions about the continuation of the pandemic at the global level, in particular on the strategy of collective immunity against the coronavirus and the development of a future vaccine, with regular reminders can. -be needed.

How many cases have been identified?

According to the medical journal

, five cases have been confirmed worldwide so far: in Hong Kong (this was the first, announced on August 24), Belgium, the Netherlands, Ecuador and in the US state of Nevada (this is the subject of a study published Tuesday).

Other cases have been described in South Korea or Israel, which gives at most less than twenty scientifically proven reinfections.

Or a drop in the ocean of positive cases (37.5 million diagnosed worldwide since the start of the pandemic).

"That doesn't mean there aren't more," warns lead author of the Nevada study, Prof. Mark Pandori.

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On the one hand, many people infected with Covid-19 do not have symptoms, which makes them difficult to spot.

The second infection of the patient from Hong Kong had also been discovered by chance, thanks to a screening test at the airport when he was returning from Europe.

On the other hand, to be sure that it is a reinfection, it is necessary to make a genetic analysis of the samples taken from each of the two infections to verify that one is indeed in the presence of two different strains of virus.

Which is cumbersome to implement on a large scale.

What consequences for patients?

It depends on the case.

In patients from Nevada and Ecuador, the second infection was more severe than the first, while the other three were not.

For scientists, the fact that the 33-year-old Hong Kong patient didn't develop symptoms the second time around is good news: it's a sign that his immune system has learned to defend itself after the first infection.

Conversely, the Nevada patient had to be hospitalized in the emergency room and given oxygen for his second infection, despite having had milder symptoms the first time.

"It's worrying," said Professor Akiko Iwasaki, an immunity specialist at Yale University (United States), in a commentary published by

.

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The authors of the study on the American patient speculated as to why his second infection was more serious.

This could be because he "was exposed to a very large dose of virus (" inoculum ") the second time around, which would have caused a more acute reaction".

Other hypotheses: a more virulent version of the virus, or the fact that the second infection was facilitated by the presence of antibodies due to the first (this may be the case in other diseases, such as dengue).

Finally, Dutch researchers recently described the case of an 89-year-old woman who died after reinfection.

But she also suffered from a rare cancer and her immune system was very low.

What consequences for the pandemic?

Reinfections revive the nagging question that the world has been asking itself since the start of the pandemic and which has not yet a definitive answer: what are the level and duration of immunity against SARS-CoV-2, the responsible coronavirus of Covid-19?

The identified reinfections took place in a relatively short period of time, four and a half months between the first and the second infection for the patient from Hong Kong and even 48 days for that from Nevada.

"The examples of other coronaviruses, responsible for common colds but also for SARS and the Seas (epidemics which broke out in 2002 and 2012, editor's note), show that there is no lifelong immunity", recently underlined a WHO expert, Maria van Kerkhove.

"People who have tested positive for SARS-CoV-2 should continue to take precautions, including physical distancing, wearing a mask and washing their hands," since reinfection is possible, advises Professor Pandori.

"Reinfections show us that we cannot rely on the immunity acquired by natural infection to achieve group immunity," writes Prof. Iwasaki, according to whom "this strategy is not only fatal for many people but also ineffective".

What consequences for a future vaccine?

"The fact that re-infections are possible could mean that a vaccine would not be completely protective. But since the number of cases is tiny, that should not dissuade us from developing them," says Pr Brendan cautiously. Wren (London School of Hygiene & Tropical Medicine), cited by the British organization Science Media Center (SMC).

"Despite all these unknowns, vaccination remains our best means of protection (against Covid-19), even if it turns out that vaccines do not provide lifelong immunity and that boosters are necessary", emphasizes for his shares the Alliance for Vaccines (Gavi) on its website.

"The problem with antibodies against coronaviruses is that they decline quickly and you can be re-infected," says Lia van der Hoek, a specialist in this family of viruses at the University of Amsterdam.

"It may therefore be that we need to repeat the vaccination all the time," she continues, risking a prediction: this coronavirus "will remain with us until the end of humanity".