(Adds comments from Butantan director, concerns about data transparency)
By Eduardo Simões
SAO PAULO, Jan 7 (Reuters) - A COVID-19 vaccine developed by China's Sinovac Biotech was 78% effective in a late-stage Brazilian trial and entirely prevented severe cases, researchers said on Thursday, boosting Chinese efforts to catch up with Western vaccine makers.
The announced efficacy, closely watched by developing countries counting on the vaccine to begin mass inoculations, was weaker than preliminary findings from Turkish researchers and lacked detailed data provided on U.S. and European vaccines.
The director of Brazilian biomedical center Butantan, Sinovac's research and production partner, said detailed results were being submitted to health regulator Anvisa as part of a request for emergency use of the vaccine.
Brazil and Indonesia, which have the most COVID-19 cases in Latin America and Southeast Asia, respectively, are preparing to roll out the 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% success rate of vaccines from Moderna Inc or Pfizer Inc with partner BioNTech SE, it is easier to transport and can be stored at normal refrigerator temperatures.
The 78% efficacy rate is still well above the 50% to 60% 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 late-stage trials last year, before receiving emergency use authorizations in the United States and elsewhere.
Butantan Director Dimas 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, Covas said there had been 218 COVID-19 cases in the trial of 13,000 volunteers. Just over 160 cases were found among the half of participants who received a placebo and the rest were among vaccinated volunteers, he said.
Brazil's CoronaVac trial included elderly volunteers, unlike other studies of the vaccine.
Covas said CoronaVac had entirely prevented severe COVID-19 cases among the vaccinated group, including the elderly. None of those who received the vaccine become ill enough to require hospitalization, he added.
Piecemeal disclosure of results from global CoronaVac studies have led to concerns about transparency of the trials, adding to skepticism about the Chinese vaccine in Brazil. Nearly half of Brazilians said they would not take a COVID-19 vaccine developed by China, according to a December poll.
Brazilian President Jair Bolsonaro has expressed disdain for the Sinovac vaccine, citing doubts about its "origin." He has traded barbs with political rival João Doria, the governor of Sao Paulo, which is funding trials and production of the shot.
Brazil has the world's second-deadliest outbreak after the United States and aims to vaccinate 51 million people, or about one-fourth of its population, in the first half of 2021, although immunizations have not yet begun.
Doria reiterated that Sao Paulo, the country's most affluent and populous state, expected to start vaccinations on Jan. 25.
China has at least five COVID-19 vaccines in late-stage trials, developed by Sinovac, Sinopharm, CanSino Biologics and the Chinese Academy of Sciences, underscoring its efforts to develop a homegrown vaccine to challenge Western rivals.
Since the new coronavirus emerged in late 2019 in the central Chinese city of Wuhan, President Xi Jinping has pledged to make China's vaccines a global public good.
The latest positive data follows China's approval on Dec. 31 of a vaccine developed by an affiliate of Sinopharm that showed 79.3% efficacy, pointing to progress China has made in the global race to develop successful vaccines.
Although China has been slower than several other countries in approving the vaccines, it has inoculated more than 2 million people since July under an emergency use program, using three different shots from Sinovac and Sinopharm that are still undergoing late-stage trials.
Based on traditional vaccine technology using inactivated coronavirus to trigger an immune response, CoronaVac can be stored at normal fridge temperatures of 2-8 degrees Celsius (36°-46°F) and may remain stable for up to three years.
Vaccines offered by Pfizer/BioNTech and Moderna use a novel synthetic messenger RNA (mRNA) technology, requiring far colder temperatures for shipping and storage.
(Reporting by Eduardo Simões Additional reporting by Ana Mano, Anthony Boadle and Beijing Newsroom Editing by Brad Haynes, Miyoung Kim and Bill Berkrot)
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