Mine Tanriover and colleagues1 report that the efficacy of CoronaVac against laboratory-confirmed symptomatic COVID-19 in a trial in Turkey is 83·5% (95% CI 65·4–92·1). By contrast, the efficacy of CoronaVac against symptomatic COVID-19 has been estimated at 50·7% (36·0–62·0) in a Brazilian trial and at 65·3% (20·0–85·1) in an Indonesian trial.2, 3 Noting that post-vaccination neutralising antibody titres are quite strongly associated with vaccine efficacy against symptomatic infection,4, 5 the efficacy estimated from the Turkish dataset is much higher than we would expect given the modest post-vaccination neutralising antibody titres after the second dose of CoronaVac.
There was a high proportion of hospitalised COVID-19 cases in the placebo group, accounting for six (19%) of the 32 cases included in the interim analysis,1 compared with 6% and 0% of cases in the Brazilian and Indonesian trials, respectively.2, 3 It is possible that some milder cases were missed in this trial, and the efficacy could therefore be skewed towards a higher value given that CoronaVac, similar to other COVID-19 vaccines, has a higher efficacy against severe disease than mild disease. Moreover, the short median follow-up time of 15 days (IQR 8–20) at risk could reduce the generalisability of the findings.
Given the global shortage of vaccines, the approval and distribution of as many effective vaccines as possible will maximise the number of lives saved during the COVID-19 pandemic. However, reports of a high efficacy in clinical trials that are not borne out by real-world vaccine effectiveness data would damage confidence in vaccines.
© 2021 Onur Coban/Anadolu Agency/Getty Images
BJC reports honoraria from AstraZeneca, GlaxoSmithKline, Moderna, Roche, and Sanofi Pasteur and is supported by the AIR@innoHK programme of the Innovation and Technology Commission of the Hong Kong Government. MEM is supported by the Research Grants Council of Hong Kong.
References
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