Heterologous versus homologous COVID-19 booster vaccination in previous recipients of two doses of CoronaVac COVID-19 vaccine in Brazil (RHH-001): A phase 4, non-inferiority, single blind, randomised study

The LancetClemens SAC, Weckx L, Clemens R, et al. | January 25, 2022

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There has been a wide use of the inactivated whole-virion SARS-CoV-2 vaccine (CoronaVac, Sinovac) in a two-dose schedule. Researchers herein examined boosted immune responses following receipt of a third dose of the homologous or a different vaccine.

  • Brazilian adults (18 years and older) in São Paulo or Salvador who had received two doses of CoronaVac 6 months previously were enrolled in RHH-001, which is a phase 4, participant masked, two center, safety and immunogenicity study.

  • A recombinant adenoviral vectored vaccine (Ad26.COV2-S, Janssen), an mRNA vaccine (BNT162b2, Pfizer–BioNTech), or a recombinant adenoviral-vectored ChAdOx1 nCoV-19 vaccine (AZD1222, AstraZeneca) was the third heterologous dose used, compared with a third homologous dose of CoronaVac.

  • A RedCAP computer randomization system was used to perform random assignment of participants (5:6:5:5) stratified by site, age group (18–60 years or 61 years and over), and day of randomization, with a block size of 42.

  • Of 1,240 participants randomly assigned to one of the four groups, 1,239 were vaccinated and 1,205 were eligible for inclusion in the primary analysis.

  • There were low antibody concentrations at 6 months after previous immunization with two doses of CoronaVac.

  • However, significant increase in binding and neutralizing antibodies occurred after all four vaccines administered as a third dose, which could improve protection against infection.

  • Following heterologous boosting, more robust immune responses were observed when compared with those observed following homologous boosting and hence heterologous boosting might increase protection.

Read the full article on The Lancet

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