A coronavirus vaccine developed by Sinovac Biotech in China was found to be only 50.4% effective in preventing symptomatic COVID-19 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 huge disappointment for Brazil, as the Chinese vaccine is one of two vaccines the federal government has lined up to begin vaccination in the second wave of the world’s deadliest COVID-19 epidemic .
Several scientists and observers have criticized the Butantan Institute, a 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. It’s not the ideal vaccine, ”said microbiologist Natalia Pasternak, criticizing Butantan’s triumphant tone.
Brazilian researchers last week celebrated results showing 78% effectiveness against “mild to severe” COVID-19 cases, a rate they later described as “clinical effectiveness.”
But they said nothing at the time about a cluster of “very mild” infections among those who had received the vaccine but did not need clinical assistance.
Ricardo Palacios, medical director of clinical research in Butantan, said on Tuesday that the new less effective result included data on these “very mild” cases.
“We need better communicators,” said Gonzalo Vecina Neto, professor of public health at the University of Sao Paulo and former director of Brazilian health regulator Anvisa.
One-off disclosures about Chinese vaccine trials around the world have raised concerns that they may not have been subjected to the same public scrutiny as alternatives being developed by US and European manufacturers.
Palacios and officials from the Sao Paulo state government, which funds Butantan, stressed that none of the volunteers inoculated with the vaccine were to be hospitalized for symptoms of COVID-19.
Public health experts have said that alone would be a relief for Brazilian hospitals that are buckling under pressure from the rising number of cases. However, it will take more time to stem the pandemic with a vaccine that allows so many mild cases.
“It’s a vaccine that will kick off the process of fighting the pandemic,” Pasternak said.
Delays and disappointment
Butantan researchers have delayed announcing their results three times, accusing a confidentiality clause in a contract with Sinovac.
In the meantime, Turkish researchers said last month that the vaccine was 91.25% effective based on an interim analysis. Indonesia gave approval for the emergency use of the vaccine on Monday based on provisional data showing it is 65% effective.
Butantan officials said the design of the Brazilian study, which focused on frontline health workers during a severe outbreak in Brazil that included elderly volunteers, made it impossible to directly compare the results with other trials. or vaccines.
Yet the COVID-19 vaccines used by Pfizer Inc with its partner BioNTech SE and Moderna Inc have been shown to be around 95% effective in preventing the disease in their crucial last-stage trials.
The disappointing data from CoronaVac is the latest setback for vaccination efforts in Brazil, where more than 200,000 people have died since the outbreak began – the worst toll outside the United States.
Brazil’s national immunization program is currently based on the Chinese vaccine and the vaccine developed by the University of Oxford and AstraZeneca.
Anvisa, who has stipulated an efficacy rate of at least 50% for vaccines in the pandemic, has already pressed Butantan for more details on his study after filing an emergency use authorization on Friday.
AstraZeneca failed to deliver active ingredients to Brazil over the weekend, leaving the government scrambling to import finished doses of the vaccine from India to begin inoculations.