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The Brazilian clinical trial for a Chinese Covid-19 vaccine has been suspended after health authorities reported a “severe adverse incident”.
Brazilian health regulator Anvisa said the incident had taken place on 29 October but gave no further details.
The suspension reportedly followed the death of a volunteer, but it is not clear if it was related to the trial.
Dimas Covas, the head of the Butantan institute conducting the trials, said there had been no adverse reactions.
Mr Covas told reporters the suspension had caused “indignation” and that the organisers of the trials had not been consulted.
The CoronaVac vaccine, developed by Chinese firm Sinovac Biotech, is one of several in final-stage testing globally.
Sinovac says it is “confident in the safety of the vaccine”.
The firm has already been using it to immunise thousands of people at home in an emergency use programme.
Brazil has been one of the countries worst affected by coronavirus, recording more than 5.6m confirmed cases – the third highest tally in the world after the US and India – and nearly 163,000 deaths, according to data collated by Johns Hopkins University.
On Monday Anvisa said it had “ruled to interrupt the clinical trial of the CoronaVac vaccine after a serious adverse incident”.
It did not reveal what had happened, nor where it had taken place. Late-stage trials for the Sinovac vaccine are also being conducted in Indonesia and Turkey, but neither of these countries have announced a suspension.
Indonesia’s state-owned Bio Farma said on Tuesday that its own Sinovac vaccine trials were “going smoothly”, according to Reuters news agency.
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Dimas Covas, the head of Butantan, told local media that the trial’s suspension was related to a death, but insisted that the death was not linked to the vaccine.
“We found this Anvisa decision strange, because it is unrelated to the vaccine. There are more than 10,000 volunteers at this moment,” he told TV Cultura.
In a press conference on Tuesday, Mr Covas said he hoped trials would resume soon.
Sinovac said on Tuesday that it was communicating with Brazil about the reported incident.
“We learned the head of Butantan Institute believed that this serious adverse event [SAE] is not related to the vaccine,” it said in a statement. “The clinical study in Brazil is strictly carried out in accordance with GCP [Good Clinical Practice] requirements and we are confident in the safety of the vaccine.”
A pause in a clinical trial is not unusual. In September, the UK paused trials for another Covid-19 vaccine after a participant had a suspected adverse reaction.
The trials for the vaccine being developed by AstraZeneca and Oxford University were resumed a few days later after regulators said it was safe to continue.
Brazil’s President Jair Bolsonaro has been open about his preference for the vaccine being developed by AstraZeneca, saying his government would not buy a Chinese-made Covid-19 vaccine.
In a Facebook post on Tuesday, he described the suspension as “another personal victory” over São Paulo Governor João Doria.
Is the decision by Anvisa based on science or politics? That’s the question many people are asking here because the issue of the vaccine – indeed, Covid-19 itself – is deeply political in Brazil.
From the very start, Jair Bolsonaro played down the virus, insisting the country remain open, that coronavirus was just the sniffles. But that approach was at odds with many of the country’s regional leaders – even people he used to count as friends.
João Doria is the governor of Brazil’s most populous (and wealthy) state. In 2018, he backed Mr Bolsonaro to become president. But the two men have since fallen out – badly.
When Covid-19 hit, Mr Doria led the way among state governors in introducing quarantine, advising people to stay at home. And that irritated Mr Bolsonaro. The governor’s backing of the Sinovac vaccine has also grated.
But it’s a rivalry that won’t be going away any time soon. Mr Doria is expected to throw his hat in the ring for the 2022 elections too – which is why, perhaps, Mr Bolsonaro is feeling a little bit competitive.
CoronaVac is one of around a dozen vaccines in the final stage of testing – known as a phase 3 trial – around the world.
This is a crucial point in vaccine development, where some experimental vaccines will fail.
The news of its suspension in Brazil came shortly after a rival vaccine developer, the US pharmaceutical company Pfizer, said its own vaccine candidate had shown 90% effectiveness.
Last month the Oxford vaccine trial reviewed the death of a volunteer in Brazil, saying an assessment had revealed no safety concerns.
Separate to the phase 3 trials being held overseas, China is also administering experimental Covid-19 vaccines at home.
CoronaVac is among three experimental coronavirus vaccines China has been using to inoculate hundreds of thousands of people under an emergency use programme.
Sinovac has previously said almost all of its employees and their families have received the vaccine.
And a Chinese health official earlier said that serious side effects have not been observed in clinical trials.
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