RIO DE JANEIRO: Brazil's health regulator said on Monday (Nov 9) it had suspended clinical trials of a Chinese-developed COVID-19 vaccine after an "adverse incident" involving a volunteer recipient, a blow for one of the most advanced vaccine candidates.
The setback for CoronaVac, developed by Chinese pharmaceutical firm Sinovac Biotech, came on the same day US pharmaceutical giant Pfizer said its own vaccine candidate had shown 90 per cent effectiveness, sending global markets soaring and raising hopes of an end to the pandemic.
The Brazilian regulator, Anvisa, said in a statement it had "ruled to interrupt the clinical trial of the CoronaVac vaccine after a serious adverse incident" on Oct 29.
It said it could not give details on what happened because of privacy regulations, but that such incidents included death, potentially fatal side effects, serious disability, hospitalisation, birth defects and other "clinically significant events".
Dimas Covas, the head of Sao Paulo's medical research institute Butantan that is conducting the Sinovac trial, said the regulator's decision was related to a death but added he found it strange "because it's a death 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," Covas told local broadcaster TV Cultura.
The institute also said it "is investigating in detail what happened", and "is at the Brazilian regulatory agency's disposal to provide any clarification necessary on any adverse incident the clinical trials may have presented".
It is not uncommon for clinical trials to be suspended temporarily - sometimes for as short as a week - after a volunteer dies or is taken ill, so that trial organisers can check whether it is related to the drug being tested.
CoronaVac has been caught up in a messy political battle in Brazil, where its most visible backer has been Sao Paulo Governor Joao Doria, a top opponent of far-right President Jair Bolsonaro.
The Sao Paulo state government said in a statement it "regrets that it learned of the decision from the press, instead of directly from Anvisa", and was waiting along with the Butantan Institute for more information on "the real reasons for the suspension".
Bolsonaro has labelled CoronaVac the vaccine from "that other country", and pushed instead for a rival vaccine developed by Oxford University and pharmaceutical firm AstraZeneca.
Last month, Bolsonaro shot down a plan by his own health minister to buy 46 million doses of CoronaVac, saying, "The Brazilian people will not be anyone's guinea pig" and referring to it as "Joao Doria's Chinese vaccine".
Doria announced earlier Monday that the first 120,000 doses of CoronaVac would arrive in Sao Paulo on Nov 20.
His state has a deal with Sinovac to buy a total of 46 million doses – 6 million produced in China and the remainder produced in Sao Paulo, which broke ground last week on a factory to produce the vaccine domestically.
"Officials in the state government fear Bolsonaro will use technical decisions to delay the timeline of the vaccine for political reasons," newspaper Folha de Sao Paulo reported, citing unnamed Doria allies.
Anvisa told AFP it had no comment beyond its statement announcing the suspension, which said that halting trials was standard procedure in such cases.
Sinovac on Tuesday stood by the safety of its COVID-19 vaccine, saying the "adverse incident" was "unrelated to the vaccine".
"We are confident in the safety of the vaccine," Sinovac said in a statement.
Bolsonaro faces criticism for his handling of the pandemic, which has included downplaying the virus, opposing lockdown measures and relentlessly promoting the drug hydroxychloroquine despite studies showing it is ineffective against COVID-19.
Brazil has the second deadliest coronavirus outbreak outside the United States, with more than 160,000 dead and more than 5.6 million confirmed cases.
The Sinovac, Pfizer and Oxford vaccines are all in Phase 3 trials, the final stage of testing before regulatory approval.