increased frequency of cases of reinfections since Omicron

published on Friday, April 01, 2022 at 1:11 p.m.

The frequency of possible reinfections with SARS-Cov2 has increased markedly since last December and the spread in France of the Omicron variant, the French Public Health Agency pointed out on Friday.

After a short stabilization in early January, the proportion of possible cases of reinfection reported to all Covid cases has been on the rise again since the end of January and now represents 5.4% of all confirmed cases, according to the latest available data. .

Possible cases of reinfection are defined as all persons who presented at least two positive tests recorded in the database carried out 60 days apart or more.

The time between the two episodes of infection was 242 days on average, the health agency said on Friday during its weekly press briefing.

In all, 685,858 possible cases of reinfection were identified between March 2, 2021 and March 20, 2022, including 95.2% since December 6, 2021, which marks the start of the distribution of the Omicron variant in France.

“It seems likely that the attenuation of the post-infectious or post-vaccination immune response within the French population plays a role in this marked increase in the frequency of possible cases of reinfection, in particular in people who have not had booster dose of the vaccine”, commented Public Health France.

“It is also very likely that the very strong distribution in France of the Omicron variant, characterized by increased transmissibility and significant immune escape, amplifies this phenomenon”, she added.

The upward resumption of the circulation of SARS-Cov2 observed for several weeks in France and the emergence of the Omicron BA.2 sub-lineage, which has dominated since the end of February, are “two factors that may play a role in the current trend to the increase in the number of reinfections”, according to Public Health France.

Several recent studies have demonstrated the possibility of occurrence of reinfection with BA.2 following infection with BA.1, including within a very short period of time (less than 60 days).

Nevertheless, they agree on the fact that these are probably rare events, underlines the agency. In addition, the frequency of reinfections with a result suggestive of Omicron during the two episodes of infections remains very low (less than 1% of cases).

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