Researchers: China’s Sinovac Coronavirus Shot over 20% Less Effective than First Claimed

A health worker prepares a vaccine during the Saban Community Clinic Vaccine Drive Up for
VALERIE MACON/AFP via Getty Images

Full data shows China’s Sinovac vaccine candidate, “CoronaVac,” to be 50.38 percent effective against the Chinese coronavirus in late-stage trials, Brazilian state researchers revealed Tuesday, according to the Wall Street Journal.

The figure is nearly 30 percentage points lower than the 78 percent efficacy rate for CoronaVac which the São Paulo state government-funded Butantan Institute previously announced on January 7.

Butantan is currently running final-stage clinical trials for CoronaVac, a Chinese coronavirus vaccine candidate developed by China’s Sinovac Biotech. The institute submitted new data to Brazil’s federal health regulator at a press conference on January 12, listing CoronaVac’s efficacy rate as just under 50.4 percent.

CoronaVac’s previous efficacy rate of 78 percent “only included volunteers who suffered mild to severe cases” of the Chinese coronavirus, Butantan said Tuesday, according to the Wall Street Journal.

“When data from all volunteers is considered, including those who contracted ‘very mild’ cases of Covid-19 [Chinese coronavirus] and required no medical assistance, the total efficacy rate falls to 50.38 percent,” the institute clarified.

“Ricardo Palácios, medical director of clinical research at Butantan, said the lower efficacy rate was caused by the inclusion of patients who were infected with the novel coronavirus but only displayed ‘very light’ symptoms,” the South China Morning Post (SCMPreported Tuesday.

Butantan staged a January 7 press conference in which it declared the results of CoronaVac’s clinical trials “fantastic” and the vaccine’s efficacy rate to be 78 percent. The global scientific community criticized the institute for including “little data” in its announcement and for reports that “[China’s] Sinovac has muzzled its Brazilian collaborators,” Science magazine noted at the time.

“In a formal presentation of the data at Butantan today [January 7], [Butantan Director Dimas Tadeu] Covas made no mention of case numbers, saying the data will be reported in a scientific publication and to Brazilian regulators. But when pressed by journalists, he allowed that there were 218 cases of mild disease,” the magazine reported.

“The exact number is 160-something in the placebo group and less than 60 in the vaccinated group,” Covas said.

“This would equal 63 percent, not 78 percent, efficacy,” Science noted of the figures.

São Paulo State Gov. João Doria plans to start a vaccination campaign for the state’s 46 million residents on January 25, but must first receive approval from Brazil’s federal regulatory agency, Anvisa, to use the CoronaVac. São Paulo state has independently contracted for CoronaVac and its Butantan Institute is Sinovac’s partner in Brazil.

Doria is a political adversary of Brazilian President Jair Bolsonaro, who has “publicly discredited CoronaVac, equating it with ‘death and disablement,’ and said he would not include it in the country’s national immunization program,” according to the SCMP on Tuesday.

“Doria … has actively pushed the Chinese-made vaccine, in what political observers say is an early move for a 2022 presidential bid,” the newspaper noted.

Brazil’s federal government has secured up to 100 million doses of the Chinese coronavirus vaccine created by the British-Swedish pharmaceutical company AstraZeneca for use in the country, but the shots will not be mandatory.

“No one can force a person to take something whose consequences are yet unknown,” Bolsonaro told reporters in the national capital, Brasilia, on January 7.


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