Policy & Regulation
Data from Brazil's late-stage trials of China's Sinovac COVID-19 vaccine show lower efficacy than expected
13 January 2021 -

The Butantan Institute and the Government of São Paulo in Brazil, in a statement published on 12 January 2021, said that a COVID-19 vaccine developed by China's Sinovac Biotech (Sinovac) was just 50.38% effective in late-stage trials in Brazil, significantly lower than earlier results showed, CNN reported on Wednesday.

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

This is now raising questions as to the veracity of the data and fuelling skepticism over the apparent lack of transparency regarding Chinese vaccines.

The statement said: "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)."

According to CNN, this 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.

This vaccine was reportedly studied in 12,500 volunteers, all of them health professionals, across Brazil.

Reportedly, 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 COVID-19 infection was included, therefore yielding a lower efficacy rate for the vaccine.

Ricardo Palacios, medical director for clinical research at the Butantan biomedical centre in Sao Paulo, was quoted as saying during a news conference: "Regarding the overall efficacy of the analysis, we met the requirements of the World Health Organization with 50.38%."

However on 12 January 2021, 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.