SAO PAULO — Brazil's health regulator halted clinical trials of the potential coronavirus vaccine CoronaVac, citing an "adverse, serious event," according to a statement it posted to its website Monday night.
The potential vaccine is being developed by Chinese biopharmaceutical firm Sinovac and in Brazil would be mostly produced by Sao Paulo's state-run Butantan Institute. Butantan said in a statement that it was surprised by Anvisa's decision and that it would hold a news conference Tuesday.
The CoronaVac shot has stirred controversy in Brazil, where President Jair Bolsonaro has cast doubt on its prospective effectiveness. He sparked confusion last month when he publicly rejected it, saying Brazilians would not be used as guinea pigs. The declaration followed news that his health minister, Eduardo Pazuello, had agreed to purchase CoronaVac doses produced locally by Butantan.
Bolsonaro has often expressed mistrust of China, particularly on the campaign trail in 2018, although he has softened his rhetoric somewhat in office. Sao Paulo state Gov. João Doria has become a political rival and an outspoken critic of the president's pandemic response.
Anvisa said in its statement that the event prompting the trial's suspension occurred Oct. 29, without saying what transpired.
"With the interruption of the study, no new volunteer can be vaccinated," its statement said.
Temporary halts of drug and vaccine testing are relatively common. In research involving thousands of participants, some are likely to fall ill. Pausing a study allows researchers to investigate whether an illness is a side effect or a coincidence. Last month, two drugmakers resumed testing of their prospective coronavirus vaccines in the U.S. after they were halted earlier.
CoronaVac is being tested in seven Brazilian states, plus the federal district where the capital Brasilia lies.
