Reinfection by covid-19: more common after 65 years

It is known that a large majority of Sars-Co-V-2 infections trigger the production of antibodies to fight the disease. The main unknown is how long this protection lasts. A first study seemed to indicate that for the elderly and the less seriously affected patients, this immunity would be short-lived. In this case, is reinfection with the virus possible? Danish researchers answer in the affirmative. Although this phenomenon of reinfection remains rare, it is nevertheless more frequent in people over 65 years of age.

In a study large-scale coronavirus reinfection rates carried out on more than 4 million people in Denmark and published in The Lancet, Researchers the Staten Serum Institute and the University of Copenhagen in Denmark, and the European Center for Disease Prevention and Control in Sweden, confirm that a tiny fraction of people with covid-19 (0.65%) tested positive twice. But they specify that 0.60% of those under 65 who had had Covid-19 during the first wave, tested positive again during the 2e vague, compared to 0.88% among those 65 and over.

They add that a previous infection would give people under 65 about 80% protection against re-infection, but that for people 65 and over, it would only give 47% protection. A discovery not really surprising since we know that the immune system weakens with age.

Partial immunity is in place

Inserm researchers have also take stock of what we know and on the still incomplete data on reinfection by covid-19. “In the current state of knowledge, most scientists agree in saying that the phenomenon of reinfection remains rare “they declare.

The first spring studies were “cautiously optimistic, “suggesting some degree of immunization against the virus after a first infection. But more recently, scientists confirmed the possibility of reinfection. A study published in the journal Clinical infectious Disease thus showed that a patient had been infected twice at 142 day intervals, but remained asymptomatic the second time. By studying the genome of the virus, they discovered that this patient had been infected with two different strains of SARS-CoV-2.

“While re-infected people may be suffering from a lack of immune response, the available data suggests that some form of immunity, even partial, sets in after first contact with the virus. It remains to be seen how many how long such protection can last and what is its degree of long-term effectiveness “, Inserm researchers point out.

The results of current vaccine trials, which require a precise analysis of the immune response of volunteers, could provide a first answer.

First proven case of reinfection in China

Who is this patient? He is a 33-year-old man, a computer scientist in Hong Kong. On March 26, he tested positive for Covid following the appearance of symptoms (cough, fever, headache). He recovered, his test was negative. Five months later on August 15, after a stay in Spain, he was tested at Hong Kong airport where the tests were compulsory. He tested positive again although he did not develop any symptoms this time. Researchers at the University of Hong Kong decide to sequence the virus and in fact find two strains: in March, it would have been infected with the “Asian” strain and in August it would be the “European” strain, the one that was transferred.

This is not the first time that reinfection has been suspected. For example, at the start of the epidemic, Korean patients apparently cured, since they tested negative when they left the hospital, were then tested positive again.

What can we deduce from this? If this scenario holds true, it may be good news from an immunity standpoint. Regularly called upon, the immune system would keep in mind the correct response to be given to Sars-CoV-2 and even contaminated, we would then develop asymptomatic forms. It remains to be seen, however, whether or not one is contagious, while being infected a second time?

The other question concerns the possible mutations of the virus. “So far, Sars-CoV-2 has mutated little. But, generally speaking, the more a virus evolves in a hostile environment, the more it undergoes a selective pressure which promotes mutations. If the virus circulates in immune individuals, he would probably have to adapt, change in order to survive, ”commented on August 26 in Figaro, researcher Bruno Canard.

Short-term immunity

This would also confirm a study of the prestigious King’s College London, relayed by The Guardian, according to which the immunity acquired after recovering from Covid-19 could disappear within a few months. Researchers had studied the immune response of more than 90 confirmed Covid-19 cases. Conclusion: the neutralizing antibodies, capable of destroying the virus, peaked on average about three weeks after the onset of symptoms and then declined rapidly. Indeed, 16.7% (only) of the cases studied still had high levels of neutralizing antibodies 65 days after the onset of symptoms.

Vaccine might be more difficult to develop

The consequence is that this may complicate the development of a vaccine that is effective in the long term. Concretely, the vaccines under development must either generate a stronger and more durable protection compared to natural infections, or be administered regularly. “If the infection gives you antibody levels that decrease over two to three months, the vaccine will potentially do the same,” and “one injection may not be enough,” commented Dr. Katie Doores, interviewed. in the Guardian.

There can be immunity without detecting antibodies at high levels in the blood

It could also call into question the principle of collective immunity, which let us remember, consists in acquiring immunity for all, once a high percentage of the population has been infected and therefore individually acquired immunity.

You should know, however, that immunity is not based only on antibodies. “Even if you end up without detectable circulating antibodies, that doesn’t necessarily mean you don’t have protective immunity because you probably have immune memory cells which can quickly kick in to start a new immune response if you encounter the virus again. It is therefore possible that you contract a milder infection, “recently argued professor of viral immunology Mala Maini, consultant at University College London.

While waiting to learn more, remember thathave a positive test, should not involve slackening the barrier gestures.

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