SAO PAULO • A coronavirus vaccine developed by China's Sinovac Biotech was 78 per cent effective in a late-stage Brazilian trial, with no severe Covid-19 cases, researchers said, although a lack of data details stirred calls for more transparency.

The trial results, closely watched by developing countries counting on the vaccine to begin mass inoculations to help end a raging pandemic, came in below preliminary findings from Turkish researchers and lacked detailed data provided on US and European vaccines.

Dr Dimas Covas, director of Brazil's biomedical centre Butantan, which is Sinovac's research and production partner, on Thursday said detailed results were being submitted to health regulator Anvisa as part of a request for emergency use of the vaccine.

Dr Cristina Bonorino, who is on the Brazilian Immunology Society's scientific committee, said a presentation at a news conference is one thing, but "it's something else to get the data and analyse it, which is what Anvisa will do".

"If it's what they say, that's an excellent result," she added.

Brazil and Indonesia, which have the most Covid-19 cases in Latin America and South-east Asia, respectively, are preparing to roll out Sinovac's vaccine, called CoronaVac, this month. Turkey, Chile, Singapore, Ukraine and Thailand have also struck supply deals with Sinovac.

Although CoronaVac's efficacy falls short of the 95 per cent success rate of vaccines from Moderna and Pfizer-BioNTech, it is easier to transport and can be stored at normal refrigerator temperatures.

The 78 per cent efficacy rate is also well above the 50 per cent to 60 per cent benchmark set by global health authorities for vaccines in development early in the pandemic, given the urgent need.

Moderna and Pfizer-BioNTech released detailed results of their late-stage trials last year, before receiving emergency use authorisations in the United States and elsewhere.

Dr Covas told a news conference that full CoronaVac data would be released in an unspecified scientific publication, but did not provide a timeline.

Pressed by journalists, Dr Covas said there had been 218 Covid-19 cases in the trial of 13,000 volunteers. Just over 160 of those cases occurred among participants who received a placebo, and the rest were in vaccinated volunteers, he added.

Unlike other studies of the vaccine, Brazil's CoronaVac trial included elderly volunteers, a particularly vulnerable population.

Dr Covas also said CoronaVac had entirely prevented severe Covid-19 cases among the vaccinated group, including the elderly. None of those who received the vaccine became ill enough to require hospitalisation, he said.

PARTIAL DISCLOSURE

Piecemeal disclosure of results from global CoronaVac studies has also led to concerns about transparency of the trials, a situation not helped by Butantan's news conference.

"It was not clear or transparent," said Dr Denise Garrett, an epidemiologist who worked for 23 years at the US Centres for Disease Control and Prevention. "They presented secondary outcomes on preventing mild cases, serious ones and hospitalisations, but not the efficacy in preventing disease."

The partial disclosure by Butantan, which had delayed its announcement three times, citing obligations to Sinovac, added to scepticism in Brazil about the Chinese vaccine.

Nearly half of Brazilians said they would not take a Covid-19 vaccine developed by China, according to a poll last month.

Brazilian President Jair Bolsonaro has expressed disdain for the Sinovac vaccine, citing doubts about its "origin". He has traded barbs with his political rival Joao Doria, the Governor of Sao Paulo. The state is funding trials and production of the shot.

Still, Health Minister Eduardo Pazuello said on Thursday that the federal government would buy Butantan's full output of CoronaVac this year, nearing a deal to secure 100 million doses for a national immunisation programme.

Brazil has the world's second-deadliest outbreak after the US, with a death toll that passed 200,000 on Thursday. It aims to vaccinate 51 million people, or about one-fourth of its population, in the first half of this year.

Immunisations have not yet begun. Mr Doria reiterated that Sao Paulo, the country's most affluent and populous state, expects to start vaccinations on Jan 25.

REUTERS