Sinovac's Covid-19 Vaccine Shown Effective in Brazil Trials

People involved in the Brazilian trials, which completed Phase 3 last week, told The Wall Street Journal that the results showed CoronaVac with an effective rate above 50%, the threshold for a vaccine to be considered viable by international scientists. The people declined to give any further information. But scientists tracking the vaccine’s development say they expect it to show efficacy comparable to other Covid-19 vaccines that have proven 95% effective in trials.

“Everyone is hoping for an efficacy rate above 90%,” said Domingos Alves, a professor at Ribeirão Preto Medical School in São Paulo who specializes in analyzing health data. “The results from the first phases of trials were very good.”

Brazil’s Butantan Institute, the research center backed by the São Paulo state government that has been testing CoronaVac, is poised to announce the vaccine’s efficacy rate on Wednesday. Butantan said Monday that it considers any information given at this time on the vaccine’s efficacy as “mere speculation.”

As wealthy nations buy up doses of vaccines from Western drugmakers, poorer countries have pinned their hopes on China. Sinovac’s CoronaVac vaccine can also be kept in a standard refrigerator at between about 36 and 46 degrees Fahrenheit, making it easier to transport and store in less-developed regions.

São Paulo Gov. João Doria has spearheaded the Brazilian development of the Chinese vaccine, which is expected to be one of the first approved for use in the hard-hit Latin American country. Brazil has registered more than 187,000 deaths from Covid-19 so far and continues to report tens of thousands of new cases each day—grim facts that make it an ideal testing ground for vaccines.

About 11,000 health workers in Brazil’s capital and across seven other states took part in the Phase 3 trials, with half taking CoronaVac and the other half receiving a placebo, São Paulo’s government said.

More than 200 of those volunteers contracted Covid-19 during the trials, giving researchers a large enough sample to calculate the vaccine’s efficacy by counting how many of those infected volunteers took CoronaVac or the placebo, Butantan’s director, Dimas Covas, said in an interview.

Mr. Covas said the Phase 3 results were being reviewed by an independent committee made up of five scientists, who would confirm an efficacy rate. While he declined to identify the specialists, Mr. Covas said they were from countries other than Brazil or China.

The results of the trials will be submitted to drug regulators in both Brazil and China on Wednesday. Mr. Covas said it is possible CoronaVac would be approved in China before Brazil.

In Brazil, the vaccine has been at the center of a bitter political fight between Mr. Doria and President Jair Bolsonaro, who has dismissed the disease as nothing more than a “little flu.”

A fierce critic of China, Mr. Bolsonaro has refused to buy CoronaVac for other states, and recently suggested on social media that the vaccine could cause disabilities and even death. Some doctors fear that Mr. Bolsonaro could put pressure on the country’s regulator, Anvisa, to delay its approval.

Mr. Doria said he planned to launch a television campaign to persuade Brazilians to get vaccinated, and would do whatever it takes to get Anvisa to approve CoronaVac in time to start administering the vaccine in São Paulo on Jan. 25.

“If necessary, we will go to the Supreme Court to save lives,” Mr. Doria said in an interview.

Mr. Doria said he plans to vaccinate the entire state, home to about a fifth of Brazil’s population, by the end of July—almost a year earlier than the federal government has promised to vaccinate the rest of the country’s population.

If people refuse to take the vaccine, they will be barred from shopping malls, cinemas, theaters, and refused entry on airplanes and buses, Mr. Doria said. “They will find themselves excluded.”

A former television star and businessman, Mr. Doria said he had the support of the private sector in the state to enforce the measure.

Butantan, which began production of Sinovac’s vaccine in Brazil this month, has agreed with the private Chinese firm to become the distributor for CoronaVac in Latin America. In May, Butantan plans to start shipping the vaccine to Argentina, Bolivia, Colombia, Honduras, Peru, and Uruguay, Mr. Covas told the Journal.

Butantan, which funded the Phase 3 trials, will use any profits from the vaccine’s distribution to reinvest in the factory it is building to produce as many as a million doses of CoronaVac daily, Mr. Covas said.

Latin American countries have scrambled to secure enough Covid-19 vaccines for the region, which has registered more than 450,000 deaths so far from the disease.

Colombia is initiating a limited testing phase for vaccines this week, President Ivan Duque said, with mass vaccinations commencing in February when the country is slated to receive its first large vaccine shipment, nearly two million doses from Pfizer Inc.

In Argentina, President Alberto Fernandez’s government reached a deal with Russia to receive 10 million doses of the Sputnik V vaccine. Last month Argentina also signed a deal with AstraZeneca PLC to receive 22 million doses of its vaccine. It expects to begin receiving those vaccines in the first half of next year.

Meanwhile, Peru’s government is coming under criticism over its failure to secure Covid-19 vaccines, as authorities say they don’t know exactly when the first batch of shots will arrive in the hard-hit country

—Ryan Dube in Lima, Peru, contributed to this article.

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Write to Samantha Pearson at samantha.pearson@wsj.com and Luciana Magalhaes at Luciana.Magalhaes@wsj.com