A coronavirus vaccine developed by China’s Sinovac Biotech was just 50.4% effective at preventing symptomatic infections in a Brazilian trial, researchers said on Tuesday, barely enough for regulatory approval and well below the rate announced last week.
The latest results are a major disappointment for Brazil, as the Chinese vaccine is one of two that the federal government has lined up to begin immunization during the second wave of the world’s second-deadliest COVID-19 outbreak.
Several scientists and observers blasted the Butantan biomedical center for releasing partial data just days ago that generated unrealistic expectations. The confusion may add to skepticism in Brazil about the Chinese vaccine, which President Jair Bolsonaro has criticized, questioning its “origins.”
“We have a good vaccine. Not the best vaccine in the world. Not the ideal vaccine,” said microbiologist Natalia Pasternak, criticizing Butantan’s triumphant tone.
Last week, the Brazilian researchers had celebrated results showing 78% efficacy against “mild-to-severe” COVID-19 cases, a rate they later described as “clinical efficacy.”
They said nothing at the time about another group of “very mild” infections among those who received the vaccine that did not require clinical assistance.
Ricardo Palacios, medical director for clinical research at Butantan, said on Tuesday that the new lower efficacy finding included data on those “very mild” cases.
“We need better communicators,” said Gonzalo Vecina Neto, a professor of public health at the University of Sao Paulo and former head of Brazilian health regulator Anvisa.
Indonesia gave Sinovac Biotech’s COVID-19 vaccine its first emergency use approval outside China on Monday as the world’s fourth most populous country launches nationwide inoculations to stem surging infections and deaths.
A lack of data and varying efficacy rates reported for the vaccine from different countries could undermine public trust in the rollout, according to public health experts.
Interim data from a late-stage human test of CoronaVac showed it is 65.3% effective, Indonesia’s food and drugs authority BPOM said - lower than figures in Brazil and Turkey which have yet to launch mass vaccinations.
BPOM head Penny K. Lukito said the results met the requirements of the World Health Organization’s minimum efficacy of 50%.