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Brazil researchers now say China’s Sinovac vaccine is 50% effective — lower than announced earlier

  • Brazil's Butantan Institute is the first to complete late-stage trial of CoronaVac, a Covid-19 vaccine developed by China's Sinovac Biotech.
  • The institute had said last week that late-stage trial data showed CoronaVac was 78% effective among volunteers with mild to severe infections, reported the Wall Street Journal.
  • But on Tuesday, the institute said the vaccine's overall efficacy rate fell to 50.4% when including "very mild" cases that did not require medical assistance, the Journal reported.

Covid-19 vaccines developed by China's Sinovac Biotech are displayed during a press conference in Beijing on Sept. 24, 2020.Wang Zhao | AFP | Getty Images

The Covid-19 vaccine developed by China's Sinovac Biotech is just 50.4% effective in a Brazilian trial — barely meeting the threshold for regulatory approval and well below the initially reported efficacy rate, according to several media reports.  

Brazil is the first to complete late-stage trial of the vaccine CoronaVac. The state-run Butantan Institute has been criticized by scientists and health experts for a lack of transparency in making public its trial data.

The institute reportedly delayed releasing trial results three times — which it blamed on a confidentially clause in its contract with Sinovac — and last week announced partial data that showed an efficacy rate that was later revised much lower.

Butantan said last week that CoronaVac was 78% effective among volunteers with mild to severe infections, reported the Wall Street Journal. But the institute said Tuesday that the overall efficacy rate fell to 50.4% when including "very mild" cases that did not require medical assistance, the Journal reported.   

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

Sinovac did not immediately respond to CNBC's emailed request for comment.

Hope for China's vaccines

Brazil and other developing nations have pinned their hopes on Chinese vaccines as wealthier countries snap up vaccines developed in the West.

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