Brazilian researchers testing China’s Sinovac vaccine said on Tuesday that the complete data shows that it is 50.38% effective against Covid-19 in final-stage tests, almost 30 percentage points less than previously announced, as concerns about the transparency of the study are growing.
The Butantan Institute, based in São Paulo, said last week that tests at an advanced stage showed that the CoronaVac vaccine is effective between 78% and 100%, offering total protection against severe cases of the disease.
However, after increasing pressure from scientists, some of whom accused the trial’s organizers of deceiving the public, Butantan said these rates include only volunteers who suffered from mild to severe Covid-19 cases. When data for all volunteers are considered, including those who contracted “very mild” cases of Covid-19 and did not require medical assistance, the total effectiveness rate drops to 50.38%, Butantan said on Tuesday.
Despite having one of the lowest efficacy rates for any new coronavirus vaccine, CoronaVac is still more effective than some flu vaccines and can be stored inexpensively in a regular refrigerator, making it a viable option for developing countries, public health experts said.
However, the fragmented and unorthodox announcement of the CoronaVac effectiveness rate, which was initially scheduled to be announced last month, risks damaging the credibility of a vaccine that many Brazilians are already reluctant to take, doctors said.