Risk factors for SARS-CoV-2 infection after primary vaccination with ChAdOx1 nCoV-19 or BNT162b2 and after booster vaccination with BNT162b2 or mRNA-1273: A population-based cohort study (COVIDENCE UK)

Background Little is known about how demographic, behavioural, and vaccine-related factors affect risk of post -vac-cination SARS-CoV-2 infection. We aimed to identify risk factors for SARS-CoV-2 infection after primary and booster vaccinations. Methods This prospective, population-based, UK study in adults (>= 16 years) vaccinated against SARS-CoV-2 assessed risk of breakthrough SARS-CoV-2 infection up to February, 2022, for participants who completed a pri-mary vaccination course (ChAdOx1 nCoV-19 or BNT162b2) and those who received a booster dose (BNT162b2 or mRNA-1273). Cox regression models explored associations between sociodemographic, behavioural, clinical, phar-macological, and nutritional factors and test-positive breakthrough infection, adjusted for local weekly SARS-CoV-2 incidence.Findings 1051 (7.1%) of 14713 post-primary participants and 1009 (9.5%) of 10 665 post-booster participants reported breakthrough infection, over a median follow-up of 203 days (IQR 195-216) and 85 days (66-103), respec-tively. Primary vaccination with ChAdOx1 (vs BNT162b2) was associated with higher risk of infection in both post -primary analysis (adjusted hazard ratio 1.63, 95% CI 1.41-1.88) and after an mRNA-1273 booster (1.26 [1.00-1.57] vs BNT162b2 primary and booster). Lower risk of infection was associated with older age (post-primary: 0.97 [0.96 -0.97] per year; post-booster: 0.97 [0.97-0.98]), whereas higher risk of infection was associated with lower educational attainment (post-primary: 1.78 [1.44-2.20] for primary/secondary vs postgraduate; post-booster: 1.46 [1.16-1.83]) and at least three weekly visits to indoor public places (post-primary: 1.36 [1.13-1.63] vs none; post -booster: 1.29 [1.07-1.56]). Interpretation Vaccine type, socioeconomic status, age, and behaviours affect risk of breakthrough infection after primary and booster vaccinations.