SAO PAULO/BEIJING - Brazil's health regulator has suspended a clinical trial for China's Sinovac coronavirus vaccine citing a severe adverse event, delighting President Jair Bolsonaro, who has criticized it for lacking credibility amid growing geopolitical tensions as the global race for a COVID-19 vaccine continues.

Brazil's health regulator, Anvisa, said late on Monday that the event occurred on Oct. 29 but did not specify if it took place in Brazil or in another country. It also did not give an indication of how long the suspension might last.

Anvisa's decision surprised trial organizers, who said there had been a death but it was unrelated to the vaccine.

"As there are more than 10,000 volunteers at this moment, deaths can occur ... It's a death that has no relation with the vaccine and as such it is not the moment to interrupt the trials," Dimas Covas, the head of Sao Paulo's medical research institute Butantan, which is conducting the Sinovac trial, told local broadcaster TV Cultura.

Brazil's suspension of the trial, one of Sinovac's three large late-stage studies, and the resulting fallout underlines the increasingly fraught political atmosphere surrounding the development and distribution of potential vaccines.

The setback to Sinovac's efforts contrasts with good news from Pfizer Inc, which said on Monday that its experimental COVID-19 vaccine is more than 90% effective based on initial trial results.

U.S. President Donald Trump, who lost the U.S. election and has repeatedly blamed China for being the source of the coronavirus, has accused Pfizer of delaying its announcement until after the vote.

Bolsonaro, a longtime China skeptic and ideological ally of Trump's, has dismissed the Sinovac vaccine as lacking in credibility. On Tuesday morning, he said on his Facebook page that the suspension was "another victory for Jair Bolsonaro."

Hu Xijin, the editor-in-chief of The Global Times, published by the People's Daily, the official newspaper of China's Communist Party, suggested on Tuesday that the proximity of the U.S. and Brazilian announcements was suspicious.

"The timing is a little strange," he said on social media platform Weibo. "I am very worried that politics and the excessive pursuit of economic interests are deeply involved in the information release on vaccines."

A World Health Organization spokeswoman sought to play down the politics.

"I don't think you need to try to find reasons or explanations other than the fact that people who are looking for a vaccine ... are very cautious," Fadela Chaib said.

TRIAL HALTED

Sinovac said in a statement on its website on Tuesday it was confident in the safety of its vaccine and will continue to communicate with Brazil on the matter. It has previously said it expects interim results of late-stage trials this year.

Butantan plans to hold a news conference on Tuesday at 11 a.m. local time (1400 GMT).

It is not uncommon for clinical trials to be suspended temporarily - sometimes for as short as a week - after a volunteer dies or takes ill so that trial organizers can check whether it is related to the drug being tested.

Sinovac's vaccine is among the three experimental COVID-19 vaccines that China has been using to inoculate hundreds of thousands of people under an emergency use program. A Chinese health official said on Oct. 20 that serious side effects have not been observed in clinical trials.

Bolsonaro has previously said the federal government will not buy the vaccine, although he had appeared to soften his position before his celebratory social media post on Tuesday.

His stance has set a clear political battleline with the governor of Sao Paulo, Joao Doria, who has said his state will both import the vaccine and produce it. Work has even begun on a plant capable of producing 100 million doses a year.

Doria, who is widely expected to challenge Bolsonaro at the next presidential election in 2022, has said a public inoculation program in Sao Paulo with the Sinovac vaccine would likely be rolled out as early as January.

Sinovac is also hoping to supply its experimental coronavirus vaccine to more South American countries by outsourcing some manufacturing procedures to Butantan.

Late stage trials are also being conducted in Indonesia and Turkey. Indonesia's state-owned Bio Farma said on Tuesday that its Sinovac vaccine trials were "going smoothly."

Four vaccines are being tested in Brazil seeking Anvisa approval, including those developed by Oxford University/AstraZeneca Plc and Johnson & Johnson's pharmaceutical subsidiary Janssen.

Pfizer's vaccine, developed in partnership with BioNTech SE, is undergoing late-stage tests involving 3,100 volunteers in Sao Paulo and Bahia states.

Worldwide, there are at least 10 vaccine candidates in late-stage clinical trials, according to the World Health Organization. Four of them are from China. REUTERS