• While the vaccination against the coronavirus continues, the Toulouse University Hospital has just released a new study on the antibody levels of hospital nursing staff in the Pink City.

  • If the protection rate of infected people was 84.8% after six months after contracting Covid-19, it drops to 56.1% a year later.

  • The study also shows that infected people who have received one or two doses are better protected than vaccinated people, who themselves are better protected than people who have had Covid-19 but who have not received their injection.

Among those who contracted Covid-19 last year, some believe their antibodies are still doing their job to defend them against a new infection.

And some say that there is no urgent need to be vaccinated.

A preconceived idea that circulates a lot and that researchers from the virology laboratory of the Toulouse University Hospital wanted to verify.

These were not starting from scratch.

Last year, they launched a large study among caregivers at the Pink City hospital.

They had been able to demonstrate that after six months, those who had had the Covid retained stable or increasing neutralizing antibodies in 96.7% of cases.

And that in absolute terms, they had an 84.8% chance of not contracting it again.

Antibody down nine months after infection

The laboratory teams again sampled these personnel between March 30 and April 15. They then looked at how the neutralizing antibodies evolved in people who were infected and who had not been vaccinated, in those infected and who were vaccinated with one or two doses, and finally in those vaccinated with two doses but who had not. been infected.

“It showed us several things.

For people infected last year but not vaccinated, antibodies increase for up to nine months after infection and then begin to decrease.

However, 97.4% of those who still had antibodies in December 2020 keep them in March-April 2021, almost a year after their infection.

Their protection rate, which was 84.8% at six months, falls on the other hand to 56.1%, we still remain protected, ”explains Chloé Diméglio, biostatiscian in the Toulouse University Hospital virology laboratory and main author of a study published this month on the subject in the specialized magazine 

Journal of infection

.

No interest in having two doses when you have been vaccinated

Of hospital staff infected last year, 20.6% have been vaccinated since. So the researchers decided to see if this had a big impact on their antibody levels. “In these people, the titer of neutralizing antibodies is significantly higher than in those who have been infected. On the median, it is 512, which is enormous and it sometimes goes up to 8,000, which for me is the Everest of neutralizing antibodies, ”notes Chloé Diméglio.

And whether they were vaccinated with one or two doses does not change whether the infection was symptomatic or asymptomatic.

There is therefore no point in taking two doses when you have already had Covid-19.

Among those people who had tested positive for the coronavirus last year and were vaccinated at the start of the year, only 0.5% of them were re-infected.

"These re-infections are debatable because they occur very quickly after the administration of the dose of vaccine, we are not within the period of 15 days after the vaccination which considers that the vaccination is effective", continues the biostatistician.

The interest of being vaccinated is not denied, according to the study

The study could have ended there, concluding that those infected had a much lower antibody titer a year after those who had been affected by Covid-19 and decided to be vaccinated.

But the scientists decided to compare this data with those who had never been sick but received their two injections, just to see if "infected and vaccinated" is equivalent to "vaccinated at all".

They therefore formed groups of 30 people of equal age and sex to be able to compare them: one made up of “just” infected people, another of infected and vaccinated people and the third of only vaccinated people.

Our file on the coronavirus

"We can see that the titer of neutralizing antibodies in infected people is lower than in vaccinated people, for whom the median is 64. But this remains much lower than the titer of neutralizing antibodies of infected and vaccinated, even with a dose.

This shows that we have every interest in being vaccinated, whether or not we have had the Covid ”, assures Chloé Diméglio, whose other results were published in

Clinical Infection Diseases

 a few days ago.

Today, the best armed against reinfection are therefore those who have already had Covid-19 and received an injection.

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