SÃO PAULO—China’s effort to boost its image by providing Covid-19 vaccines to the developing world suffered a setback after one of its leading inoculation candidates turned out to be 50% effective in late-stage trials in Brazil, significantly lower than earlier results showed.
While Sinovac’s CoronaVac efficacy rate still meets the 50% threshold the World Health Organization considers good enough for widespread use, scientists said a lack of transparency about the data risks damaging the credibility of a vaccine Brazilians and others world-wide are already reluctant to take.
Brazil’s Butantan Institute, a São Paulo-based public institute that is the first to complete late-stage trials of the CoronaVac vaccine, had said last week that it was shown to be 78% effective and offer total protection against severe cases of the disease.
But after rising pressure from Brazilian scientists, some of whom accused the trial’s organizers of…