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.

BACKGROUND: The COVID-19 pandemic is over but the highly immunized or naturally exposed global population still requires booster vaccinations against newly emerging SARS-CoV-2 variants. We assessed safety and immunogenicity of booster doses of COVID-19 vaccines based on three different platforms in a setting that mimics the current routine practice in Brazil. METHODS: In this phase 3 study from 14 February 2023 to 12 June 2023 we enrolled previously immunized adults to receive an additional booster dose of one of three vaccines. Immunogenicity against ancestor SARS-CoV-2 and Omicron BF.7, BQ.1.1.3, and XBB.1.5.6 sub-lineages was measured as ELISA IgG or virus neutralizing (VNT) antibodies and safety/reactogenicity assessed using diary cards. RESULTS: Volunteers with a history of full primary COVID-19 immunization striated to three cohorts according to their previous booster vaccination history-0 (n = 26), 1 (n = 140) or 2 (n = 606) booster vaccinations-were randomized 2:1:1 to receive either recombinant protein (SCB-2019, Clover), adenovirus-vector (ChAdOx1-S, AstraZeneca/Fiocruz), or mRNA (BNT162b2, Pfizer/Wyeth). Baseline antibody titers were higher in individuals who had received one or two boosters and titers against both ancestor and Omicron sub-lineages increased in all groups regardless of the number of previous booster doses or the vaccine used. Day 28 geometric mean titers (GMTs) and geometric mean-fold rises (GMFR) against all variants were higher after BNT162b than SCB-2019 or ChAdOx1-S, but BNT162b groups displayed more rapid antibody waning at Day 84. Within cohorts each vaccine elicited similar GMFR against the different SARS-CoV-2 strains. All vaccines were well tolerated with similar solicited reactogenicity profiles. CONCLUSIONS: Protein, adenovirus-vector or mRNA vaccine boosters were equally well tolerated and immunogenic against ancestor SARS-CoV-2 and Omicron sub-lineages in fully primed adults with 0-2 prior boosters. BNT162b induced the highest immune responses but also the most rapid waning of antibodies 3 months after vaccination. CLINICAL TRIAL REGISTRATION:, identifier NCT05812586.

Original publication




Journal article



Publication Date



Protein vaccine, SARS-CoV-2, Vector vaccine, mRNA vaccine