The first cases of SARS-CoV-2 reinfection were reported as early as late summer 2020. In this context, Santé publique France has implemented several surveillance systems to study these events. While it is rare to be able to formally confirm a reinfection (to do so, sequencing data must be available for both episodes of COVID-19 confirming infection by two different viral strains), identifying possible cases of reinfection using the SIDEP database is a valuable tool for studying these events, particularly when a new variant emerges.

SARS-CoV-2 Reinfections in France: Key Findings

SARS-CoV-2 reinfections are not rare events, particularly in the context of widespread circulation of the Omicron variant

Nearly 417,000 possible cases of SARS-CoV-2 reinfection were identified during the study period from January 1, 2021, to January 27, 2022. However, due to a change in patient identification within the SIDEP database that makes it impossible to identify possible reinfection events with a first episode in 2020, this figure does not reflect the total number of possible reinfection cases that have occurred since the SIDEP database was established.

Possible cases of reinfection accounted for 2.8% of all confirmed COVID-19 cases, with a marked increase during the fifth wave of the epidemic. Nearly 80% of possible reinfection cases for which an interpretable screening result was available had an infection suspected to be linked to the Omicron variant during the second episode.

Possible SARS-CoV-2 reinfections are therefore not rare events, particularly given the widespread circulation of the Omicron variant during the fifth wave of the pandemic.

Young adults and healthcare workers are overrepresented among possible cases of reinfection

The proportion of adults aged 18 to 40 was significantly higher than among all confirmed COVID-19 cases (52% versus 39%), accounting for more than half of the possible reinfection cases.

Healthcare workers were overrepresented among possible cases of reinfection compared to all confirmed COVID-19 cases (6% versus 3.4%).

This overrepresentation of young adults and healthcare workers among possible reinfection cases could be explained by these populations’ increased exposure to SARS-CoV-2 infection compared to the general population, due to occupational activity or lower adherence to preventive measures and social distancing, or lower vaccination coverage among 18- to 40-year-olds compared to older age groups.