We conducted a test-negative study design at the community "Complexo da Maré", the largest group of favelas in Rio de Janeiro, Brazil, when Gamma and Delta were the predominant variants circulating. We estimated 42.4% (95% CI, 24.6, 56.0) protection against symptomatic COVID-19 after 21 days of one dose of ChAdOx1.
One-dose ChAdOx1 nCoV-19 Vaccine Effectiveness Against Symptomatic COVID-19 in a vulnerable community in Rio de Janeiro, Brazil: test-negative design study