Cookies on this website

We use cookies to ensure that we give you the best experience on our website. If you click 'Accept all cookies' we'll assume that you are happy to receive all cookies and you won't see this message again. If you click 'Reject all non-essential cookies' only necessary cookies providing core functionality such as security, network management, and accessibility will be enabled. Click 'Find out more' for information on how to change your cookie settings.

BackgroundOngoing outbreaks of coronavirus disease 2019 (COVID-19) are driven by waning immunity following primary immunizations and emergence of new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants that escape vaccine-induced neutralizing antibodies. It has been suggested that heterologous boosters could enhance and potentially maintain population immunity.MethodsWe assessed the immunogenicity and reactogenicity of booster doses of different formulations of aluminium hydroxide-adjuvanted SCB-2019 vaccine (9 μg of SCB-2019, with or without CpG-1018 adjuvant, or 30 μg of SCB-2019 with CpG-1018) in Brazilian adults primed with ChAdOx1-S vector vaccine. S-protein antibodies and ACE2-binding inhibition were measured by enzyme-linked immunosorbent assay (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 μg of SCB-2019 + CpG + aluminium hydroxide, 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 the 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, with the highest responses being with the 30-μg SCB-2019 + CpG + aluminium hydroxide formulation.Clinical trials registrationNCT05087368.

Original publication




Journal article


Open forum infectious diseases

Publication Date





Oxford Vaccine Group, Department of Pediatrics, University of Oxford, and the NIHR Oxford Biomedical Research Centre, Oxford, United Kingdom.