Key points

• 18% of confirmed COVID-19 cases in week 2022-S31 (August 1–7) were possible cases of reinfection. Between March 2, 2021, and August 7, 2022, possible reinfections accounted for 6% of all confirmed COVID-19 cases. This proportion has been rising sharply since December 2021: it was 0.7% through December 5, 2021, and 6.7% since December 6, 2021.

• 94.8% of possible reinfection cases occurring since March 2, 2021, for which an interpretable screening result was available for the second episode, are suspected Omicron variants.

• Reinfections with Omicron variants carrying a mutation at position L452 (BA.4 and BA.5 in particular) began appearing in week 2022-S18 (May 2–8) and became the majority in week 2022-S23 (June 6–12).

• For 54% of possible reinfections occurring during week 2022-S31, the first episode took place after week 2022-S01 (a period during which Omicron prevalence exceeded 90% in Flash surveys).

• The probability of reinfection increases with the time elapsed since the first infection, reaching a plateau approximately six months after the first infection.