A Randomized Clinical Trial Using CoronaVac or BNT162b2 Vaccine as a Third Dose in Adults Vaccinated with Two Doses of CoronaVac
Abstract
CoronaVac is one of the World Health Organization–approved inactivated virus vaccines, and over 750 million doses have been administered in more than 40 countries. Phase three randomized clinical trials (RCTs) of CoronaVac showed efficacies against symptomatic illness of 50.65%, 65.30%, and 83.50% in Brazil, Indonesia, and Turkey, respectively (1). Since these efficacy studies assessed outcomes within a few months after vaccination, the impact of antibody waning on virus variants has not been assessed. Breakthrough infections, some leading to severe disease and death, have been reported in CoronaVac vaccinated adults and have raised concern (2). Our recent observational study showed that the immunogenicity of CoronaVac is much lower compared with the BNT162b2 mRNA vaccine, and we estimated that waning immunity would lead to a loss of protection within a few months (3, 4). A third vaccine dose was considered for CoronaVac vaccinated individuals. Here, we report the results of an RCT to compare the immunogenicity of using BNT162b2 and CoronaVac as the third dose for adults with low antibody response to two doses of CoronaVac. Some of the results of these studies have been previously reported in the form of a preprint (medRxiv; [accessed 2021 Nov 3]; https://doi.org/10.1101/2021.11.02. 21265843). Methods Of the 360 participants who had received two doses of CoronaVac as part of our previous study (3), 260 showed surrogate neutralization test (sVNT) results below 60% in their…
How strong is the evidence?
Evidence Hub reads this as a randomized trial, done in people. Its evidence level is 2 of 5 (High · randomized trial). Randomized trials of a reasonable size are the strongest single-study design. Reported size: 360 participants or records.
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