Covid-19 Vaccine Effectiveness against the Omicron (B.1.1.529) Variant.

Abstract (PubMed)

We used a test-negative case-control design to estimate vaccine effectiveness against symptomatic disease caused by the omicron (B.1.1.529) and delta (B.1.617.2) variants in England. Vaccine effectiveness was calculated after primary immunization with two doses of BNT162b2 (Pfizer-BioNTech), ChAdOx1 nCoV-19 (AstraZeneca), or mRNA-1273 (Moderna) vaccine and after a booster dose of BNT162b2, ChAdOx1 nCoV-19, or mRNA-1273. Between November 27, 2021, and January 12, 2022, 886,774 persons infected with omicron, 204,154 infected with delta, and 1,572,621 test-negative controls were identified. Vaccine effectiveness against omicron was substantially lower than against delta at all time points. No effect against omicron was noted from 20 weeks after two ChAdOx1 nCoV-19 doses; two BNT162b2 doses showed 65.5% (95% CI, 63.9-67.0) effectiveness at 2-4 weeks, dropping to 8.8% (95% CI, 7.0-10.5) at 25+ weeks. BNT162b2 booster after ChAdOx1 primary: 62.4% (95% CI, 61.8-63.0) at 2-4 weeks. BNT162b2 booster after BNT162b2 primary: 67.2% (95% CI, 66.5-67.8) at 2-4 weeks. Primary immunization with two doses provided limited protection against omicron symptomatic disease. A BNT162b2 or mRNA-1273 booster substantially increased protection, but that protection waned over time.