Brazil said on Monday that it had halted a late-stage trial of a Chinese vaccine, which had been considered a global front-runner in the race to develop a protective shot for the coronavirus, after a “serious adverse” reaction in a participant.
The Brazilian health regulator provided little information on its decision, and did not say whether the reaction was related to the vaccine, called CoronaVac and produced by the Chinese company Sinovac, or coincidental.
The participant who had the reaction became ill on Oct. 29, according to the authorities. They did not divulge where in Brazil the vaccine had been administered or what had happened to the volunteer, citing patient confidentiality. In a statement, they said that such a “serious adverse incident” might include death, disability, hospitalization, birth defects or other “clinically significant events.”
CoronaVac is one of 11 experimental vaccines, produced by some of the world’s foremost pharmaceutical companies, currently in Phase 3 trials.
On the same day that Brazil suspended the Sinovac trial, the American company Pfizer announced that an early analysis of its coronavirus vaccine trials suggested that its drug was more than 90 percent effective in preventing the virus that causes Covid-19.
Sinovac’s drug was seen in China as a leading candidate. But in Beijing’s push to get a Chinese vaccine to be the first on the global market, officials stretched the definition of “emergency use.” They have permitted tens of thousands of people to receive the Sinovac vaccine and two other locally made vaccines, despite having not yet concluded Phase 3 trials.
Adverse effects are not unusual in Phase 3 trials. AstraZeneca and Johnson & Johnson both paused their trials after a few volunteers fell seriously ill, resuming them six weeks later, in October, after concluding that the illnesses were not related to the vaccines
The details of why the Brazilian health regulator had paused the trials were uncertain.
In a statement issued on Tuesday, Sinovac said Instituto Butantan, the medical center coordinating the Brazilian trials, had deemed the “serious event” not related to the vaccine. The company said it was “confident in the safety” of its vaccine.
According to news reports, the institute confirmed that a volunteer had died, but officials there said they were “surprised” by the government’s decision to halt the trials.
Dimas Covas, head of the institute, told a Brazilian television network that he found the government regulator’s decision strange “because it’s a death unrelated to the vaccine.”
Prof. Kim Mulholland, a pediatrician at the Murdoch Children’s Research Institute in Melbourne, Australia, called it “alarming” that Instituto Butantan appeared to have no idea why the trial had been stopped. “It leaves me wondering who had done that and why,” Professor Mulholland added. “That’s the question that really needs to be answered because this is a violation of the normal process.”
— Sui-Lee Wee The New York Times