A study conducted by the Toulouse University Hospital with 8,758 caregivers shows that nearly 97% of them had stable or rising antibodies 167 days after being infected with SARS-CoV-2.
- Covering 8,758 caregivers in Toulouse hospitals, including 276 who were infected with Covid-19, the study shows a high level, up to 85%, of protection after infection.
A great unknown at the start of the Covid-19 epidemic, the question of immunity after a first infection with the coronavirus is now better known to scientists.
After two initial studies, published successively in the British Medical Journal and in the magazine Scienceand who estimate persistent immunity 6 to 8 months after infection, the virology laboratory and the occupational health service of the Toulouse University Hospital come to a similar conclusion.
Their study, published Wednesday, January 27 in the journal Clinical Infectious Diseases from health professionals, reports the persistence of immunity up to six months after a first infection.
Acquired immunity for at least 167 days
The work was carried out from June 10 to December 9, 2020 after 8,758 caregivers to discover the prevalence of SARS-CoV-2. “We wanted to obtain a photo at the end of the first confinement on a population supposed to have been more strongly exposed to the coronavirus than the confined population”explains to the site Ladepeche.fr Chloé Dimeglio, doctor in applied mathematics, biostatistician in the virology laboratory of Pr Jacques Izopet at the Toulouse University Hospital.
Blood samples showed that 276 caregivers contracted the virus, a low prevalence of 3%. Among them, some have developed a symptomatic form, others an asymptomatic form of Covid-19.
Six months after infection (167 days), patients again underwent serological tests to assess whether or not they were immune to SARS-CoV-2. The results are particularly encouraging: 95% of caregivers carried neutralizing antibodies, even if not all had the same levels. “In 96.7% of them, their level of neutralizing antibodies was either stable or on the rise, underlines Chloé Dimeglio. Which means that the immunity acquired after a first infection with the coronavirus lasts at least six months and that is rather good news.
Natural immunity weaker than that granted by the vaccine
The researchers also found that there was a risk of reinfection. 1.8% of the 276 caregivers, or 5 people, tested positive for Covid-19 again. However, the work was unable to demonstrate a link between this reinfection and the level of neutralizing antibodies. Among the reinfected, some had high rates, others low. The protection rate due to natural immunity would be 84.8% according to the study data.
An immunity that is certainly significant, but which remains lower than that granted by the messenger RNA vaccines developed by Pfizer-BioNTech and Moderna, which is 95%. “So we have an interest in getting vaccinated. And when the Haute Autorité de Santé recommends getting vaccinated from three months after a first infection, it is consistent”concludes Chloe Dimeglio.