Brazil’s health regulator announced on Monday it had suspended clinical trials of the Chinese COVID-19 vaccine — CoronaVac, after an “adverse incident” involving a volunteer recipient, AFP reported. The setback for the Chinese vaccine, developed by pharmaceutical firm Sinovac Biotech, came on the same day US pharmaceutical Pfizer said its vaccine candidate had shown 90% effectiveness.

The Brazilian health regulator, Anvisa, said in a statement it had “ruled to interrupt the clinical trial of the CoronaVac vaccine after a serious adverse incident” on October 29.

Although it didn’t provide any further details due to privacy regulations, but that such incidents included death, potentially fatal side effects, serious disability, hospitalization, birth defects and other “clinically significant events.”

However, the public health center coordinating the trials of CoronaVac in the country, the Butantan Institute, said it was “surprised” by the decision. The institute “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 said.

Butantan Institute will hold a press conference on Tuesday at 11:00 am (1400 GMT).

Political battle in Brazil over CoronaVac

The Chinese vaccine candidate is embroiled in a political battle in Brazil as its top backer Sao Paulo Governor Joao Doria is a stern opponent of the right-wing President Jair Bolsonaro.

Doria said in September that CoronaVac had shown an immune response of 98% in the elderly, in the phase II trial. Some 9,000 volunteers had taken part in the trial.

Bolsonaro has labeled CoronaVac the vaccine from “that other country” and has 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.”

Responding to a supporter on social media who urged him not to buy the vaccine, the President said, “We will not buy the Chinese vaccine.”

Doria announced earlier Monday that the first 120,000 doses of CoronaVac would arrive in Sao Paulo on November 20.

His state has a deal with Sinovac to buy a total of 46 million doses — six million produced in China and the remainder produced in Sao Paulo.

Also read: Phase III trials of India’s COVAXIN to start in Bhubaneshwar

Among the COVID-19 vaccine candidates that are in phase III are those developed by Sinovac, Pfizer and Oxford. This is the last stage of testing before regulatory approval.

Also read: Oxford COVID-19 vaccine shows ‘strong immune response’ in all adult groups: University

All three vaccine candidates are undergoing clinical trials in Brazil — the country with the second-highest number of deaths, after the United States.

The country has witnessed over 5.6 million virus cases and more than 162,600 deaths.