ABSTRACT
BackgroundOngoing outbreaks of COVID-19 are driven by waning immunity following primary immunizations and emergence of new SARS-CoV-2 variants which escape vaccine-induced neutralizing antibodies. It has been suggested that heterologous boosters could enhance and potentially maintain population immunity. MethodsWe assessed immunogenicity and reactogenicity of booster doses of different formulations of alum-adjuvanted SCB-2019 vaccine (9 g SCB-2019 with or without CpG-1018 adjuvant, or 30 g SCB-2019 with CpG-1018) in Brazilian adults primed with ChAdOx1-S vector vaccine. S-protein antibodies and ACE2-binding inhibition were measured by ELISA on Days 1, 15 and 29. Participants self-reported solicited adverse events and reactions. ResultsAll SCB-2019 formulations increased S-protein ELISA antibodies and ACE2 binding inhibition to a greater extent than ChAdOx1-S. After 30 g SCB-2019+CpG+alum titers against wild-type S-protein were significantly higher than after ChAdOx1-S on Days 15 and 29, as were titers of neutralizing antibodies against wild-type strain and Beta, Gamma, Delta, and Omicron variants. Boosting with SCB-2019 or ChAdOx1-S was well tolerated with no vaccine-related serious or severe adverse events. ConclusionsBoosting ChAdOx1-S-primed adults with SCB-2019 induced higher levels of antibodies against a wild-type strain and SARS-CoV-2 variants than a homologous ChAdOx1-S booster, highest responses being with the 30 g SCB-2019+CpG+alum formulation.
ABSTRACT
We conducted a test-negative study design at the community "Complexo da Mare", 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.
