On Feb. 16, 2023, it was reported in the Lancet that protection from past infection against re-infection from pre-omicron variants was very high and remained high even after 40 weeks.

Protection from re-infection from ancestral, alpha, and delta variants declined over time but remained at 78ﾷ6% (49-8-93-6) at 40 weeks. Protection against re-infection by the omicron BA.1 variant declined more rapidly and was estimated at 36-1% (24-4-51-3) at 40 weeks.