SAO PAULO (Reuters) -- Brazilian researchers said on Wednesday the COVID-19 vaccine developed by China's Sinovac Biotech is more than 50% effective based on trial data, but again withheld full results at the company's request, raising questions about transparency.
Brazil is the first country to complete a late-stage trial of the vaccine, called CoronaVac, but a release of the results, first set for early December, has now been delayed three times.
The latest delay is a blow to Beijing, which has been racing to catch up with Western drugmakers, and will add to criticism that Chinese vaccine makers have lacked transparency.
It is also likely to fan growing skepticism toward the Chinese vaccine in Brazil, just as the virus roars back to life. President Jair Bolsonaro, a coronavirus skeptic who has said he will not take a COVID-19 vaccine, has repeatedly questioned the Chinese vaccine based on its "origins." A poll earlier this month showed that half of Brazilians now reject it.
Officials from the Sao Paulo state government's Butantan Institute declined to specify the efficacy rate from a trial they led with 13,000 volunteers, citing contractual obligations with Sinovac. They said, however, the vaccine was effective enough against the novel coronavirus for it to be approved for emergency use in Brazil. Health regulator Anvisa has stipulated an efficacy rate of at least 50% for vaccines in the pandemic.
"Our aim was for it to be over 50%. If it were 51%, it would be important for us, especially as we are living in a moment of a health crisis," said Sao Paulo Health Secretary Jean Gorinchteyn. "For us, it would be a moment to celebrate."
The officials said Sinovac asked them to delay releasing precise vaccine efficacy data for up to 15 days from Wednesday while the company consolidates data from global trials.
Sinovac did not immediately respond to a request for comment.
Butantan Director Dimas Covas said none of the volunteers vaccinated in Brazil's CoronaVac trial developed a severe case of COVID-19, contributing to optimism about its effectiveness.
"Having no severe cases is very good. That will be very useful for combating this pandemic," said immunologist Cristina Bonorino, who sits on the scientific committee of the Brazilian Immunology Society.
"But it hurts the image of their vaccine to have this hesitation," she added. "They shouldn't have made a show of something that in the end they didn't report. That's the bigger problem."
Sinovac would be the second Chinese vaccine maker to produce results from late-stage clinical trials, after the United Arab Emirates said this month a vaccine from a Beijing-based unit of China National Pharmaceutical Group (Sinopharm) had 86% efficacy.
Rival products developed by AstraZeneca Plc, Pfizer Inc and Moderna Inc have generated positive results.
Pfizer's treatment, developed with German partner BioNTech SE, was the first fully tested COVID-19 shot to be administered, with rollout already begun in the UK, the United States and Canada.
China has been giving experimental coronavirus vaccines, including the shot developed by Sinovac, to high-risk groups in the country since July under an emergency use program.
Sinovac has secured supply deals for its vaccine with several countries including Indonesia, Turkey, Brazil, Chile and Singapore, and is holding talks with the Philippines and Malaysia for a potential sale.