Why the first case of Covid-19 re-infection does not worry researchers

It was feared and it has just happened: a first case of re-infection with Covid-19 was identified in Hong Kong on Monday. But the scientific community ensures that there is no need for concern, even if this event forces us to ask new questions about the development of the epidemic.

It happened. A 33-year-old Hong Kong man has become the first person to be officially infected with SARS-CoV-2 twice. Researchers at the University of Hong Kong confirmed on Monday, August 24, that after recovering from the disease in March, the patient tested positive a second time, more than four months later, during an airport check-up when he returned from a stay in Europe.

Since the Covid-19 epidemic began, several individuals have been suspected of being infected twice. But so far, researchers have never been able to rule out the possibility of recurrence rather than re-infection.

Immunity for four to six months?

This time the researchers in Hong Kong could establish that the genetic signature of the virus that affected the 30-year-old was different from that observed during the previous contamination. In other words, the person has probably been exposed to two different strains of coronavirus. “We can be reasonably certain that this is the first recorded case of re-infection with Covid-19,” confirms Jonathan Stoye, virologist and head of research at the Francis Crick Institute in London, contacted by France 24.

As the world struggles to roll back the pandemic threat, confirmation of the hypothesis that the virus can strike the same person at least twice may seem alarming. But that did not surprise the scientific community. “We have been saying, almost since the epidemic began, that the immune system lasted between four and six months in people with a mild form of Covid-19,” said Paul Hunter, a microbiologist and infectious disease specialist at the University of East Anglia in Norwich. England), contacted by France 24. This is what seems to have happened to the young Hong Kong who during his first infection had only developed relatively mild symptoms, such as fever, cough and headache.

This first case of re-infection has also been greeted with some relief by several researchers, as it seems to indicate “that the immune response works exactly as expected. [dans le cas du Covid-19, NDLR]”, at assured on Twitter Akiko Iwasaki, virologist at Yale University. The patient is in fact asymptomatic, which means that “the body’s defenses, if one can not block the pollution because there are no more antibodies, could have prevented the onset of symptoms that affect health. “, Explains Paul Hunter.

Silent re-infection

It is therefore possible that SARS-CoV-2 strikes silently when it infects a person for the second time. “If this person had stayed abroad longer, we would probably never have shown that he was infected again,” confirms the British microbiologist. For him, waves of contamination can thus occur in the coming weeks and months without anyone realizing it.

But we must be careful “not to generalize from a single confirmed case,” warns Jonathan Stoye. The immune response to Covid-19 can vary from person to person, continues this virologist from the Francis Crick Institute. Hong Kong researchers studying the first case did not provide specific details about the 33-year-old’s background and general health. Under these conditions, it is difficult to know whether his failure with SARS-CoV-2 is not due to a peculiarity of his immune profile.

Paul Hunter admits that with only one confirmed case, it is difficult to get sure. However, the proven possibility of re-infection means that issues that have so far remained theoretical become very concrete. “One of the main questions is whether and how contagious people who are infected for the second time can be,” he states. “If other cases were to be identified, it would really be important to do in-depth serological tests to understand what the risks are,” confirms Jonathan Stoye. In this regard, the fact that the Hong Kong citizen does not show any symptoms of the disease is encouraging because “it is currently assumed that asymptomatic individuals are much less contagious than others,” Paul Hunter recalls.

Researchers at the University of Hong Kong also believe that their discovery is bad news for vaccine research. Although immunity may disappear after just a few months, the effectiveness of a vaccine may seem relative. But Paul Hunter wants to be less pessimistic on this issue: “we know that vaccines generally provide immunity, which lasts longer than what occurs naturally after contamination.”

On the other hand, for him, the 33-year-old Hong Konger has unknowingly destroyed the hopes of those who relied on collective immunity to overcome the Covid-19 epidemic. Sweden, which has adopted this strategy to avoid limiting its population, can only hope very strongly that thirty is an isolated case.