The waves follow each other, but are not alike. The number of reinfections with Covid-19 has increased sharply lately as the circulation of the virus continues to intensify on the territory, indicated, Friday, July 8, Public health France in his weekly update. According to the latest data available as of June 12, 12% of confirmed cases of Covid-19 were possible cases of reinfection. Between March 2, 2021 and June 12, 2022, possible reinfections accounted for only 4.1% of all confirmed cases.
Public Health France defines a reinfection as a new infection (detected by a positive test) which has occurred at least 60 days after a primary infection, which has occurred since March 2021. “The increase has been continuous since the arrival of the Omicron wave”, indicated Vincent Auvigne, epidemiologist from Public Health France, during a press briefing. Indeed, the vast majority (93.5%) of cases of reinfection that have occurred since March 2021 were indeed “suspected Omicron variant”.
Despite a high number of re-infections with an Omicron sub-variant after a first infection with another Omicron sub-variant (44% of cases), “the probability that a re-infection will actually occur after a first infection with a other variant (Alpha, Delta or other)” “remains significantly higher”, underlines the agency. In addition, “the further the first contamination is in time, the more the probability of reinfection will increase”, specified Vincent Auvigne.
- How to explain these reinfections?
During the week ending July 3, the circulation of Covid-19 intensified in mainland France. New hospitalizations as well as deaths have increased sharply, affecting the majority of the oldest, insufficiently vaccinated, also noted Public Health France. Thursday evening, more than 154,600 new cases of Covid-19 were recorded, with 17,719 hospitalized patients, including 1,523 new admissions.
The rebound in Sars-Cov-2 circulation and the emergence of the Omicron BA.4 and BA.5 sublineage are two factors that play a role in the current trend of increasing reinfections. Added to this is the decrease in post-infectious or post-vaccination immune protection over time in the French population. We now know that the protection conferred by vaccines and by previous infections erodes after a few months. In question, too, a relaxation of barrier gestures.
- Are they the effect of a higher immune escape in the subvariants?
Succeeding BA.2 (dominant since the beginning of the year), the BA.4 and BA.5 sub-variants have become the majority. “BA.5 represents 67% of interpretable sequences, during the Flash Week 25 survey (June 20 to 26),” says Public Health France in its epidemiological update of July 7. The BA.4 and BA.5 sub-variants propagate all the faster as they seem to benefit from a double advantage of contagiousness and immune escape.
The BA.5 strain is more transmissible than the previous ones. “A booster induces a response against this subvariant, but the efficacy is less marked than against Delta or BA.1, and it decreases rapidly. Six months after this third dose, very few neutralizing antibodies against BA are found. 5″, noted Professor Olivier Schwartz, head of the Virus and Immunity Unit at the Institut Pasteur, in L’Express on June 19.
First of all, we must sweep away the idea that multiple reinfections would strengthen our immune system, and each time make the symptoms a little less serious. If no peer-reviewed study has reached a conclusion, the subject remains open. Faced with the risk of reinfections, the “very contagious” variants require that the level of protection of the most fragile be increased”, added Gilles Pialoux, head of service at the Tenon hospital (AP-HP) in mid-June. Let’s not forget that vaccines remain effective against severe forms of the disease, hence the importance for elderly and immunocompromised people to have a complete vaccination schedule.
Already in mid-May, France was approaching one million possible cases of reinfection with Covid-19, with the outbreak of contamination linked to the Omicron variant. At the time, two categories were among the most affected: adults aged 18 to 40, and health professionals. Women had been slightly more reinfected than men.