Brazilian researchers on Tuesday announced that China’s Sinovac vaccine was far less effective than originally touted, at just 50.38 percent effective against COVID-19 in late-stage trials, nearly 30 percentage points lower than initial data showed.
The Butantan Institute in São Paulo initially said last week that late-stage trials had found the CoronaVac vaccine to be between 78 percent and 100 effective, according to the Wall Street Journal.
After a number of scientists accused the trial’s organizers of misleading the public, the institute revealed researchers had separated the cases into six categories: asymptomatic, very mild, mild, two levels of moderate, and severe. The earlier rates included only volunteers who had mild to severe cases of coronavirus.
Butantan on Tuesday clarified that when data from all volunteers is accounted for, including volunteers who contracted “very mild” cases of coronavirus and required no medical assistance, the total efficacy rate drops to 50.38 percent, one of the lowest efficacy rates for any new COVID-19 vaccine.
The vaccine just meets the 50 percent threshold required for approval by Brazilian regulators and the World Health Organization.
However, because CoronaVac was 100 percent effective in preventing severe cases, is still more effective than some flu vaccines and can be stored inexpensively in a regular refrigerator, it is a useful option for developing countries, experts said. The questions surrounding the vaccine’s efficacy may serve as a further deterrent to many Brazilians who are already wary of receiving the shot, doctors said.
While Brazil’s health regulator is reviewing a request for emergency use of CoronaVac, Sao Paulo authorities plan to begin vaccinations on January 25.
Turkey and Indonesia, which have reported different efficacy numbers in their own trials, plan to begin administering the shot this week.
Beijing is hoping much of the third world will adopt the Chinese vaccine as the U.S. and European nations rely on more effective vaccines developed by American pharmaceutical companies.
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