Antibody measurement
Plasma and serum samples were tested for antibodies against the spike receptor-binding domain of SARS-CoV-2 at Unidade de Apoio ao Diagnóstico do COVID-19 (UNADIG-RJ) using the SARS-CoV-2 IgG (Abbott, United States of America) chemiluminescent microparticle immunoassays (CMIA). Seroconversion was defined as a positive anti-SARS-CoV-2 spike antibody result in the post-vaccination sample following a negative anti-SARS-CoV-2 spike antibody result in the pre-vaccination sample. A positive anti-SARS-CoV-2 spike antibody result was defined as per the manufacturer’s defined cut-off. Researchers involved in sample processing, selection and testing were blinded to the participants randomisation group and were unaware of which COVID-19 vaccine they had received.