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.
Reuters: 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 immunisation 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.
Piecemeal disclosures about Chinese vaccine trials globally have raised concerns that they are not subject to the same public scrutiny as U.S. and European alternatives.
Palacios and officials in the Sao Paulo state government, which funds Butantan, emphasised the good news that none of the volunteers inoculated with CoronaVac had to be hospitalised with Covid-19 symptoms.
Public health experts said that alone will be a relief for Brazilian hospitals that are buckling under the strain of surging case loads. However, it will take longer to curb the pandemic with a vaccine that allows so many mild cases.