Officials at the Butantan Institute in São Paulo said a trial conducted in Brazil showed that the CoronaVac vaccine, manufactured by Beijing-based Sinovac, had an efficacy rate of just over 50 percent. That rate was far lower than the 78 percent efficacy rate announced last week.
Officials have since clarified that the higher figure pertained to the protection the vaccine offered against developing symptoms of Covid-19 significant enough to require medical treatment. While officials had asserted last week that the vaccine provided absolute protection against moderate to severe symptoms, they acknowledged on Tuesday that the data underpinning that claim was not statistically significant.
The 50 percent efficacy rate is just over the threshold the World Health Organization and the Food and Drug Administration use to assess the efficacy of vaccines.
Scientists and world leaders regard CoronaVac as a potential game-changer in fighting the pandemic because it could be rapidly produced and distributed in countries in the developing world. Unlike other vaccines, it does not require storage in freezing temperatures.
Natalia Pasternak, a microbiologist and the president of Instituto Questão de Ciência, told reporters on Tuesday that the results of the trial meant it will not be a panacea.
“It is not the best vaccine in the world,” she said at the news conference during which the efficacy rate was disclosed. But she called it a “perfectly acceptable vaccine” that would reduce the number of patients who develop serious cases or die from the virus.
Brazil’s health regulatory agency, Anvisa, is reviewing data from the trial, which relied on volunteers who are health care professionals. If Anvisa approves emergency use of CoronaVac, officials hope to start giving out shots in Brazil late this month.
Dimas Covas, the director of Butantan Institute, called the vaccine an “excellent” tool “waiting to be used in a country where currently 1,000 people are dying per day.”
President Jair Bolsonaro has spoken derisively about CoronaVac, fueling an growing anti-vaccination movement in Brazil, where more than 200,000 people have died from Covid-19. The vaccine has been championed by the São Paulo governor João Doria, who is widely expected to run for president in 2022 and is among the president’s most vocal critics.
Denise Garrett, a Brazilian-American epidemiologist and vaccine expert, said there was no reason to doubt the vaccine’s safety, adding that the data presented so far suggests it will provide a satisfactory level of protection. But Dr. Garrett said the vague and at times misleading manner in which information about the vaccine has been presented to the public stands to shake people’s confidence in its reliability and fuel the political battle over the vaccine.
“The lack of transparency really damages people’s trust,” she said. “They’ve just reinforced the narrative that this vaccine is not good.”
— Ernesto Londoño, Manuela Andreoni and Letícia Casado