Brazil Halts Trial of Chinese Coronavirus Vaccine, CoronaVac

Brazil said on Monday that it had halted a late-stage trial of a Chinese vaccine that 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, including whether the reaction was related to the vaccine, called CoronaVac and produced by the Chinese company Sinovac, or coincidental.

The suspension provoked a political outcry as critics of President Jair Bolsonaro accused the federal government of putting lives in peril by politicizing a vaccine trial. The Brazilian institute assisting with the CoronaVac trial is run by the state of São Paulo, which is led by Gov. João Doria, a political rival of Mr. Bolsonaro.

Dimas Covas, the head of Instituto Butantan, the state-run medical center involved in the study, said Tuesday that the trial’s suspension stemmed from the death of a vaccine trial volunteer on Oct. 29.

The suspension was not justified, Mr. Covas said, because the death “was not related to the vaccine.”

Gustavo Mendes, director of Anvisa, Brazil’s health regulatory agency, said in an interview on Tuesday that regulators have yet to conclude that the volunteer’s death was unrelated to the vaccine.

“It was a precautionary measure,” he said. “Unfortunately, it’s being politicized.” He added: “Halting a study until there is more information is what is expected of a regulatory agency.”

CoronaVac is one of 11 experimental vaccines, produced by some of the world’s foremost pharmaceutical companies, currently in Phase 3 trials. As the world grapples with another major wave of coronavirus infections, the race for a vaccine has intensified and been made all the more competitive by fractious geopolitics.

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.

Last month Mr. Bolsonaro reacted angrily when he learned the health ministry intended to buy 46 million doses of the vaccine.

“I ordered that it be canceled,” he said. “It appears no country in the world is interested in that Chinese vaccine.”

Mr. Doria’s party, the Brazilian Social Democracy Party, said in a statement that the race to develop a vaccine “is not a political contest and cannot be treated like one.”

It accused Mr. Bolsonaro of “putting his political aspirations above anything else, showing disregard for the lives of Brazilians.”

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.”

It is rare for a drug that has not been fully tested to be so widely administered, and scientists from around the world have repeatedly warned that the Chinese government was risking the health of its people before the completion of late-stage trials.

Sinovac’s treatment is an inactivated vaccine, meaning that it is made of a coronavirus that has either been weakened or killed by chemicals.

Tao Lina, a vaccine expert in Shanghai, said he believed that the Brazilian suspension was not based on science but on politics.

“The technology of inactivated vaccines is very mature, and the possibility of this incident being related to vaccines is very slim,” said Mr. Tao, a former immunologist at the Shanghai Centers for Disease Control and Prevention. He said the Chinese government was unlikely to halt the emergency-use program because “it will cause a lot of panic.”

Reporting was contributed by Manuela Andreoni, Letícia Casado, Elsie Chen and Muktita Suhartono. Amber Wang contributed research.