China’s Sinovac vaccine 50% effective, according to Brazilian researchers

China's Sinovac vaccine 50% effective, according to Brazilian researchers
Image source: ©Yasin Caglayan via

China’s Sinovac vaccine is only 50.4% effective, according to the late-stage trial held by Brazil’s Butantan Institute.

The Brazilian trial suggests that the Sinovac vaccine barely satisfies the standards for regulatory approval and is below the initially reported efficacy rate, based on several media reports.

However, scientists and health experts criticize the state-run Butantan Institute for a lack of transparency in making public its trial data.

Reports claim that the institute delayed publishing trial results three times because of a confidential clause in its contract with Sinovac. Partial data was released last week, showing an efficacy rate that was later adjusted much lower.

Last week, Butantan previously reported that CoronaVac was 78% effective among volunteers experiencing mild to severe infections, according to the Wall Street Journal. But the institute announced Tuesday that the overall efficacy rate of China’s vaccine dropped to 50.4% when including “very mild” cases that did not need medical assistance, the Journal furthered.


In comparison, Covid vaccines from Pfizer-BioNTech and Moderna were reported to be about 95% effective in their late-stage trials.

The CoronaVac vaccine is considered cheaper and easier in terms of transportation. It can easily be stored in ordinary refrigerators, unlike other vaccines that must be stored at subfreezing temperatures.

Brazil has recorded over 8.1 million Covid infections in total, the third highest number globally, based on the data compiled by Johns Hopkins University. The country’s death toll of over 204,000 is the second-highest in the world.

Butantan also asked for emergency use authorization for CoronaVac, according to Reuters. Brazil’s health regulator Anvisa, which set a minimum 50% efficacy rate for vaccines in the pandemic, announced that it will meet on Sunday to discuss their decision.

Other developing countries like Indonesia and Turkey are also holding trials on CoronaVac.

Indonesia has approved Sinovac for emergency use on Monday — the first country outside China to do so following a late-stage trial that reveals a 65.3% efficacy rate, reported Reuters.

Turkey said their interim analysis suggests that the vaccine is 91.25% effective, Reuters reported last month.

Singapore is also carefully reviewing the effectiveness of the Sinovac vaccine. Health Minister Gan Kim Yong explained that a coronavirus vaccine developed by China’s Sinovac Biotech must undergo regulatory scrutiny and authorization by Singapore’s Health Sciences Authority (HSA) before it can be administered to the public.

“We will go through the data carefully when it comes, rather than depending on reported numbers. It’s better to rely on official data that we receive from Sinovac itself,” he said.

The HSA will evaluate the data while the nation’s Covid-19 expert committee will determine if it can pass vaccination standards in Singapore, Gan said.

“We will share more details when it’s available,” he added.

In November, a DBS economist warned that China’s Covid vaccines may attract developing countries that may face a long wait if they want a vaccine from the West.

“Considering the billions of doses needed, and the risk [of] falling at the back of a very long line for Western vaccines, the appeal of the Chinese vaccines is apparent,” Taimur Baig, chief economist and managing director at DBS Group Research, said in a note.