Waning effectiveness of COVID-19 vaccines

Abstract

In The Lancet, Peter Nordström and colleagues1 report the effectiveness of several COVID-19 vaccines and different vaccine schedules against any documented SARS-CoV-2 infection and against severe COVID-19, for up to 9 months of follow-up. Data for 842 974 matched pairs of vaccinated and unvaccinated individuals in this retrospective cohort study were retrieved from the Swedish national registers. These registers track health outcomes for all registered individuals nationwide. Both cohorts had a median age of 52·7 years (IQR 37·0–67·5) and included mostly women (500 297 [59·3%] in each cohort) and individuals born in Sweden (703 666 [83·5%] in the vaccinated cohort vs 578 647 [68·6%] in the unvaccinated cohort). Follow-up started 14 days after the second dose for each person vaccinated with BNT162b2 (Pfizer–BioNTech), mRNA-1273 (Moderna), ChAdOx1 nCoV-19 (Oxford–AstraZeneca), or mixed ChAdOx1 nCoV-19 and an mRNA vaccine and their unvaccinated matches. Effectiveness estimates were adjusted for date of second dose, age, sex, domestic support (proxy for disability), education, place of birth, and comorbidities. The study was completed on Oct 4, 2021, before the advent of the omicron (B.1.1.529) variant.