Researchers at Butantan delayed announcement of their results three times, blaming a confidentiality clause in a contract with Sinovac. In the meantime, Turkish researchers said last month that CoronaVac was 91.25% effective based on an interim analysis. Indonesia gave the vaccine emergency use approval on Monday based on interim data showing it is 65% effective. Butantan officials said the design of the Brazilian study, focusing on frontline health workers during a severe outbreak in Brazil and including elderly volunteers, made it impossible to compare the results directly with other trials or vaccines.
Still, COVID-19 vaccines in use from Pfizer Inc with partner BioNTech SE and Moderna Inc proved to be about 95% effective in preventing illness in their pivotal late-state trials. The disappointing CoronaVac data is the latest setback for vaccination efforts in Brazil, where more than 200,000 people have died since the outbreak began – the worst death toll outside the United States. Brazil’s national immunization program currently relies on CoronaVac and the vaccine developed by Oxford University and AstraZeneca Plc – neither of which has received regulatory approval in Brazil.
Anvisa, which has stipulated an efficacy rate of at least 50% for vaccines in the pandemic, has already pressed Butantan for more details of its study, after it filed for emergency use authorization on Friday. The regulator said it will meet on Sunday to decide on emergency use requests for CoronaVac and the British vaccine. 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.