A Blog by Jonathan Low


Jan 14, 2021

Brazil Finds Chinese Covid Vaccine Less Effective Than Promised

China has tried to buy credibility in its competition with the west by claiming its vaccine was as effective  as those from the US and UK. 

But in an era of constant examination and free flowing information - especially as it regards Covid - it is becoming harder to flack misinformation. JL

Samantha Pearson reports in the Wall Street Journal:

China’s effort to boost its image by providing Covid-19 vaccines to the developing world suffered a setback after one of its leading inoculation candidates turned out to be 50% effective in late-stage trials in Brazil, significantly lower than earlier results showed. Brazil’s had said last week that it was shown to be 78% effective and offer total protection. Hours after (it) announced CoronaVac to be between 78% and 100% effective, Brazil’s federal government announced it would buy up to 100 million doses of the vaccine.

China’s effort to boost its image by providing Covid-19 vaccines to the developing world suffered a setback after one of its leading inoculation candidates turned out to be 50% effective in late-stage trials in Brazil, significantly lower than earlier results showed.

While Sinovac’s CoronaVac efficacy rate still meets the 50% threshold the World Health Organization considers good enough for widespread use, scientists said a lack of transparency about the data risks damaging the credibility of a vaccine Brazilians and others world-wide are already reluctant to take.

Brazil’s Butantan Institute, a São Paulo-based public institute that is the first to complete late-stage trials of the CoronaVac vaccine, had said last week that it was shown to be 78% effective and offer total protection against severe cases of the disease.

But after rising pressure from Brazilian scientists, some of whom accused the trial’s organizers of misleading the public, Butantan said Tuesday those rates only included volunteers who suffered mild to severe cases of Covid-19. When data from all volunteers was considered—including those who contracted “very mild” cases of Covid-19 and required no medical assistance—the total efficacy rate fell to 50.4%, Butantan said.

Sinovac didn’t respond to requests for comment.

From Latin America to Africa and Asia, many developing countries have pinned their hopes on CoronaVac and other Chinese vaccine candidates as richer nations snap up inoculations developed in the West. CoronaVac can be stored in an ordinary refrigerator, making it cheaper and easier to transport than others that require subfreezing storage temperatures.

“This will have profound implications domestically [in China] and internationally,” said Yanzhong Huang, a senior fellow for global health at the Council on Foreign Relations in New York. “From the very beginning, China has raised people’s expectations about the effectiveness of China-made vaccines.”

Beyond mainland China and Hong Kong, Turkey and Ukraine are among nations that have reported orders for CoronaVac, and where regulators would also be closely watching for efficacy analysis. Brazil has agreed to buy up to 100 million doses, and seven other Latin American countries have been in talks to obtain the vaccine.

Sinovac and Butantan had initially scheduled to reveal the efficacy rate by Dec. 15 but delayed it a week, citing a decision to collect additional data. A week later, the announcement was delayed again, which Brazilian researchers attributed to Sinovac’s request for more time to consolidate data from trials in Indonesia and Turkey.

“It’s extremely unusual, I’ve never seen this,” said Denise Garrett, an epidemiologist at the Washington-based Sabin Vaccine Institute who worked for the Centers for Disease Control and Prevention in Atlanta for more than 20 years. “They had already delayed the results—it seems they found them to be unsatisfactory so they came up with a way to announce the results in a more favorable way,” she said.

Vaccine efficacy at recommended doses











(clinical trial

in Brazil)

Minimum standard

for effective vaccine






Sources: State of Sao Paulo (CoronaVac); the companies (Covid-19 vaccines); Centers for Disease Control and Prevention (other vaccines)

The lower success rate could push governments toward giving priority to purchases from drugmakers whose vaccines have higher efficacy rates, said Iván Darío Vélez, an infectious disease expert at Colombia’s University of Antioquia.

“If the vaccine has an efficacy rate around 50%, it’s going to be hard to justify including it in the national vaccination program,” said Dr. Vélez. “But if we have a society that doesn’t have the means to acquire all of the vaccines it needs, you can see a scenario where authorities would say, ‘Fifty percent protection is still better than nothing.’”

In Chile, officials said they would go ahead with plans to import some 10 million doses of the Sinovac vaccine, the first batch of which was expected this month, said Rodrigo Yáñez, a high-ranking official in the Foreign Relations Ministry in charge of importing the shots.

Mr. Yáñez said CoronaVac would still be effective in preventing deaths and overwhelming hospitals with Covid-19 patients. “That is the objective,” he said.

Many flu vaccines have an efficacy rate even lower than that of CoronaVac, public-health specialists said.

As China brought Covid-19 under control last year, the country’s vaccine developers turned to foreign nations to conduct their clinical trials, choosing Brazil, Indonesia and Turkey. The widely differing results from those countries have only raised more questions about how well the vaccine works.

In countries with high numbers of Covid-19 cases, volunteers in vaccine trials face a greater exposure to the virus, allowing researchers to test vaccines faster and produce more accurate results. More than 200,000 people have died from Covid-19 in Brazil so far, second only to the U.S., turning the Latin American country into an ideal testing ground for vaccines.

Researchers in Turkey, which is at an earlier stage of testing CoronaVac, said late last month that initial data from around 1,300 people in late-stage trials showed the vaccine to be just over 91% effective.

Meanwhile, Indonesian authorities reported Monday that preliminary results from their clinical trial of CoronaVac showed an efficacy rate of 65.3%, although it isn’t clear how scientists there made their calculations.

Though that rate was based on data from a trial involving just 1,600 volunteers in the city of Bandung, Indonesian authorities this week greenlighted CoronaVac for emergency use. It isn’t clear whether Indonesian authorities knew the full extent of the data analysis from Brazil. The country has secured 126 million doses of the vaccine, batches of which have already arrived.

In contrast, more than 12,000 health workers took part in Phase 3 trials in Brazil, the first country to complete tests of Sinovac’s vaccine. Of those volunteers, 252 contracted Covid-19—167 of whom took the placebo, and 85 of whom took the vaccine, the Butantan Institute said Tuesday.

Butantan researchers on Tuesday defended their decision to release partial results first, saying that it is more important to know how well the vaccine protects people against more severe cases rather than all cases.

CoronaVac’s relatively low efficacy rate means more people will need to take the vaccine to achieve herd immunity, making it even more important for its developers to be transparent and reassure the public about its efficacy and safety, doctors said.

Infectious disease specialists blamed the skewed results on both pressure from São Paulo’s government and Sinovac in China.

Political observers here say that São Paulo’s Gov. João Doria, who spearheaded Butantan’s partnership with Sinovac, has politicized the vaccine’s development by championing its use in his increasingly public tussle with President Jair Bolsonaro, who has long disparaged Chinese vaccines. Mr. Doria is considered a likely presidential candidate next year.


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In November, Mr. Bolsonaro warned his followers that the CoronaVac vaccine could kill or disable them, without offering any evidence. Mr. Bolsonaro, who last year recovered from a mild case of Covid-19, has dismissed the disease as nothing more than a “little flu” and said he doesn’t plan to get vaccinated himself.

Battling politicians coupled with the mixed signals about the Sinovac vaccine led 50% of respondents in a Datafolha poll conducted last month to say they wouldn’t take any Chinese vaccine. When respondents were asked if they would get vaccinated, knowing vaccines are produced by many countries, only 20% said they would not.

“It’s absurd,” Sonia Nascimento, a 46-year-old caregiver for the elderly, said about the confusion over the vaccine’s efficacy rate. “Is this vaccine going to work? Should I wait for more people to take it in case it has side effects?”

While Butantan has found itself caught in a political battle in Brazil, its Chinese partners imposed strict controls on what information could be publicly shared.

“Butantan found itself squashed between them in the middle of all this mess,” said Eliseu Waldman, an epidemiologist at the University of São Paulo, who like many specialists has defended the 120-year-old institution. Butantan produces the majority of vaccines used in the country and is in talks to distribute CoronaVac throughout South America.

Hours after Butantan announced CoronaVac to be between 78% and 100% effective last Thursday, Brazil’s federal government announced it would buy up to 100 million doses of the vaccine.

Chinese authorities approved CoronaVac for emergency use last July but have yet to approve the vaccine for broad use. The Council on Foreign Relations’ Mr. Huang says the lower efficacy figure doesn’t preclude China from still allowing the vaccine to be used widely.


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