China drugmaker fact-checks claim that its leading COVID vaccine is 97% effective

December 8, 2020, 11:14 AM UTC

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On Tuesday, Sinovac, one of China’s leading vaccine makers, said it needs more time to determine the effectiveness of its COVID-19 vaccine, refuting earlier claims from its partner in Indonesia that its vaccine proved 97% effective in ongoing Phase III clinical trials.

Bio Farma, the state-owned vaccine maker and Sinovac’s partner in Indonesia, reported that Sinovac’s COVID-19 candidate is up to 97% effective in Phase III clinical trials. “Our clinical trial team found, within one month, that the interim data shows up to 97% for its efficacy,” Iwan Setiawan, a spokesman for Bio Farma, said on Tuesday.

But Sinovac clarified to Bloomberg that the 97% figure does not refer to the vaccine’s efficacy, saying it instead represented the vaccine’s seroconversion rate. The seroconversion rate detects whether the vaccine produces COVID-19 antibodies—meaning the vaccine triggered antibodies in 97% of trial volunteers who received it—but doesn’t necessarily prove that the vaccine protects against COVID-19. Sinovac did not immediately return Fortune’s request for comment.

Ninety-seven percent efficacy would be the best clinical trial data reported from any vaccine maker thus far: U.S.-based firms Pfizer and Moderna reported efficacy rates of 94% and 95%, respectively, in Phase III trials in the U.S.

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But Bio Farma drew its conclusion about Sinovac’s efficacy from a smaller pool of participants, some 1,600, and in a shorter time frame.

Pfizer, which codeveloped its candidate with Germany’s BioNTech, reported in November that it drew its 94% efficacy figure from a 43,000-participant Phase III trial that began in July. Moderna’s Phase III trial also started that month and included 30,000 volunteers.

A spokesperson for Bio Farma said on Tuesday that full results from Sinovac’s Phase III trial are expected to arrive in January 2021.

Sinovac’s Phase III trial results have been highly anticipated because its vaccine does not require the expensive cold-chain networks that are needed for Pfizer’s and Moderna’s candidates, making it a more viable option for lower- and middle-income countries with fewer resources. Such a vaccine is key to bringing the pandemic to a swift end since it can be more widely distributed than doses with finicky storage requirements.

On Monday, Indonesian President Joko Widodo said that Indonesia received 1.2 million doses of Sinovac’s vaccine candidate, called CoronaVac, in preparation for potentially distributing the vaccine in Indonesia early next year. Indonesia is also set to receive another 1.8 million CoronaVac doses in January along with raw material supplies for Bio Farma to produce 45 million more doses of the candidate.

On Monday, Sinovac received a $515 million investment from Beijing drugmaker Sino Biopharm. Sinovac said the new stream of funding would help the company double its manufacturing capacity to produce over 600 million doses of CoronaVac per year.

Authorities in Brazil, Turkey, and Chile have also approved Sinovac’s Phase III clinical trials. In Brazil, Sinovac’s Phase III trial has reached an advanced stage; it started in July and includes 13,000 individuals. Observers believe that the company may release interim results on the trials in coming days.

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