(CNN)A leading Chinese Covid-19 vaccine developed by 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 Sao Paulo Tuesday.
While the number exceeds the threshold required for regulatory approval, it falls far below the 78% previously announced, raising questions as to the veracity of the data and fueling skepticism over the apparent lack of transparency regarding Chinese vaccines.
Analysts said the efficacy rate of Sinovac's Coronavac vaccine in Brazil -- the lowest among its global competitors -- could affect international confidence in Chinese-made vaccines and hamper Beijing's effort to repair its image from its early mishandling of the initial outbreak by providing Covid-19 vaccines to developing countries.
"The Butantan Institute and the Government of Sao 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 margin for regulatory approval is likely to lead to concern among scientists, given that last week the Butantan institute released partial "clinical efficacy" results celebrating 78% to 100% efficacy in preventing infections.
The state body financed the phase 3 trials of the vaccine, which involved 13,000 health workers across eight Brazilian states.
Sao Paulo Gov. Joao Doria holds a box of Sinovac's Coronavac vaccine during a news conference on November 19, 2020 in Sao Paulo, Brazil.
"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.
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. We have to wait for ANVISA (Brazilian Health Regulatory Agency) to evaluate."
A representative of Sinovac said the company is discussing the result but declined to give further comment. The final efficacy rate of the vaccine will be determined by China's drug regulator, the National Medical Production Administration, according to the representative.
