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Chinese pharmaceutical firm Sinovac says its COVID-19 vaccine is more than 50 percent effective, but data withheld

Vials and boxes of Sinovac Biotech's vaccine, called CoronaVac, are displayed at a media event in Beijing on Sept. 24.Nicolas Bock/Bloomberg

(Bloomberg) -- A COVID-19 vaccine developed by Chinese pharmaceutical firm Sinovac Biotech Ltd. was found to be more than 50 percent effective in a Brazilian clinical trial, though researchers delayed releasing more information at the request of the company.

A 50 percent efficacy rate is a minimum standard set by US regulators for emergency authorization of Covid vaccines. Messenger RNA vaccines from Moderna Inc. and Pfizer Inc. have produced far better results, reducing symptomatic Covid cases by well over 90 percent in giant trials.

Chinese vaccine developers have been slow compared with their western peers in releasing efficacy data on their shots. As millions of healthy people count on transparency in trials before taking a shot, the lack of more specific results from Sinovac’s trial risks eroding confidence in Chinese vaccines. Hong Kong on Wednesday said residents will be allowed to choose which shot they want to take among several candidates that will likely include Sinovac’s.

The lack of transparency in reporting the Brazil trial results “is totally unacceptable,” and wouldn’t pass muster in the US, Eric Topol, a clinical trials expert and director of the Scripps Research Translational Institute, said in a phone interview. “This doesn’t have a good look to it at all.”


Sinovac didn’t respond to repeated calls seeking a comment. State-backed newspaper Global Times said in response to what it called western media “hyping up questions about transparency” that the delay had nothing to do with “fake data.” It said the company will gather and analyze data from trials in other countries like Turkey and Indonesia before finalizing a complete picture.

The late-stage trial of Sinovac’s vaccine in Brazil, involving about 13,000 participants, suggested the shot is “safe and effective,” authorities at the Butantan Institute and from the state of Sao Paulo said. They were asked to not disseminate the information until it was thoroughly reviewed in China as part of a contractual agreement, they said.


“Our goal was for the shot to be more than 50 percent effective,” state Health Secretary Jean Gorinchteyn said at a press conference. “A vaccine that reaches at least that is already cause for celebration.”

The group that received the vaccine in Brazil’s trial had no severe cases of Covid-19, and the main side effect reported was mild pain at the injection site, said Dimas Covas, head of Butantan. Efficacy is above the threshold needed for a vaccine to be registered by Brazil health regulator known as Anvisa, which still has to approve the shot, he said.

The trial produced efficacy data that differed from tests carried out in other countries, Gorinchteyn said, without elaborating. He added that Sinovac’s review of the data is slated to take 15 days but could take less than that, and shouldn’t delay the planned Jan. 25 start of inoculations with the Sinovac shot.

“Sinovac has several ongoing trials, and it’s important it gives the data consistency,” Covas said. “The company can’t analyze data from the same vaccine using different criteria, and can’t have three different efficacy rates for the same vaccine.”

It is routine for trials of a drug or vaccine conducted in different groups of patients or locations to produce slightly different results, and research groups typically report results of independent trials separately.

Yet while Butantan and state authorities reiterated their optimism for the shot, Topol said the fact that Brazilian authorities would only say that the vaccine is more than 50 percent effective, but not provide any more detail, suggests that Sinovac efficacy results may not be as good as those achieved by Pfizer and Moderna.


Sinovac is betting on a successful vaccine to inoculate more people around the world and save lives, especially in developing countries like Brazil that will have limited access to the Pfizer and Moderna shots. Vaccines from Sinovac and other Chinese companies could also help their home country win geopolitical influence and restore an image tarnished by the criticism of its initial response to the virus.

Sinovac’s shot is potentially more suited to developing countries because it can be kept at normal refrigerator temperatures. By contrast, the mRNA vaccines from Pfizer and Moderna require deep-freeze conditions for storage and transportation, making distribution more complicated.

China has allowed emergency use of its frontrunner vaccines since mid-year and plans to inoculate 50 million people in frontline industries by early February, Bloomberg News has reported. A shot developed by state-owned China National Biotec Group Co., a unit of Sinopharm, protected 86 percent of people against Covid-19, according to a statement from the health ministry in the United Arab Emirates. Neither CNBG nor Sinopharm has commented on the UAE announcement, nor released interim efficacy data directly.

China’s drug regulator will review an application by a Sinopharm unit that developed one of the company’s two inactivated vaccines, according to local Chinese news website Jiemian, citing a screen shot of the regulator’s Center for Drug Evaluation website. In Hong Kong, the government has agreed to receive 7.5 million doses of Sinovac’s vaccine.


The data delay on the Sinovac shot is a blow to Sao Paulo Governor Joao Doria’s plan to obtain swift approval and begin vaccinating the state of some 45 million people in January. He’s attempting to move quickly while the central government drags its feet on supply agreements and concrete vaccination dates. Millions of doses of Sinovac’s vaccine, called CoronaVac, have already been shipped to Sao Paulo.

The Sinovac vaccine has been at the center of a political dispute between Doria and President Jair Bolsonaro, who says a vaccine from China can’t be trusted.