June 21, 2022
Effects of Previous Infection and Vaccination on Symptomatic Omicron Infections
NEJM study shows that mRNA vaccine effectiveness turns negative by six months while prior infection retains strong effectiveness against infection.
“The protection conferred by natural immunity, vaccination, and both against symptomatic SARS-CoV-2 infection with the BA.1 or BA.2 sublineages of the omicron variant is unclear.
We conducted a national, test-negative, case–control study in Qatar from Dec. 23, 2021 through Feb. 21, 2022 to evaluate the effectiveness of vaccination with BNT162b2 (Pfizer–BioNTech).
MRNA-1273 (Moderna), natural immunity due to previous infection with variants other than omicron, and hybrid immunity (previous infection and vaccination) against symptomatic omicron infection and against severe or fatal COVID-19
Previous infection was associated with a 50% reduced risk of infection…Two-dose vaccination had negligible effectiveness against BA.1 and BA.2″
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