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 Butantan Institute and the Government of São Paulo report that the coronavirus vaccine achieved a 50.38% overall efficacy rate in the clinical study conducted in Brazil, in addition to [an efficacy rate of] 78% for mild cases and 100% for moderate and severe cases of Covid-19. All rates are higher than the 50% level required by the WHO (World Health Organization),” the statement released Tuesday said.
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.
“Regarding the overall efficacy of the analysis, we met the requirements of the World Health Organization with 50.38%,” Ricardo Palacios, medical director for clinical research at the Butantan biomedical center in Sao Paulo said Tuesday during a news conference.
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.