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Chinese Covid-19 Vaccine Is Far Less Effective Than Initially Touted in Brazil


Brazilian researchers testing China’s Sinovac Vaccine said Tuesday that full data showed it to be 50.38% effective against Covid-19 in late-stage trials, almost 30 percentage points lower than previously announced, as concerns grow over the study’s transparency.

The São Paulo-based Butantan Institute said last week that late-stage trials had shown the CoronaVac vaccine to be between 78% and 100% effective, offering total protection against severe cases of the disease.

However, after rising pressure from scientists, some of whom accused the trial’s organizers of misleading the public, Butantan said those rates only included volunteers who suffered mild to severe cases of Covid-19. When data from all volunteers is considered, including those who contracted “very mild” cases of Covid-19 and required no medical assistance, the total efficacy rate falls to 50.38%, Butantan said 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 cheaply in an ordinary refrigerator, making it a viable option for developing countries, public health experts said.

However, the piecemeal and unorthodox announcement of CoronaVac’s efficacy rate, which was first scheduled to be announced last month, risks damaging the credibility of a vaccine that many Brazilians are already reluctant to take, doctors said.

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