Brazil data shakes confidence in China’s Sinovac coronavirus vaccine

A Covid-19 vaccine developed by China’s Sinovac Biotech was just 50.38% effective in late-stage trials in Brazil, significantly lower than earlier results showed, according to a statement published by the government of São Paulo Tuesday.

While the number meets the threshold required by global regulators for approval, it falls far below the 78% figure announced last week.

It’s raising questions as to the veracity of the data and fueling skepticism over the apparent lack of transparency regarding Chinese vaccines.

The razor-thin results for regulatory approval are likely to lead to concern among scientists, given that last week the Brazilian Institute released partial “clinical efficacy” results celebrating 78% to 100% efficacy in preventing infections. The vaccine was studied in 12,500 volunteers, all of them health professionals, across Brazil.

Why the data changed: In a summary of the clinical study published by the government of São Paulo and the Butantan Institute, data for another group of participants who reported “very mild” cases of infection was included, therefore yielding a lower efficacy rate for the vaccine.

Questions over efficacy: However on Tuesday, high-ranking members of the Brazilian Health Ministry told CNN affiliate CNN Brasil that “the effectiveness is borderline,” and that because “it is at the limit” they would need the county’s health regulator agency, ANVISA, to evaluate.

A representative of Sinovac said the company is discussing the result but declined to give further comment. 

Last week, ANVISA told the Butantan Institute that in order to approve the emergency use of a vaccine, the global efficacy rate had to be disclosed to the public — information the institute did not receive from Sinovac at the time, according to CNN Brasil sources.