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Sinovac claims progress with early coronavirus vaccine study.

Sinovac, a Beijing-based drugmaker,said on Saturdaya vaccine it's developing for the new coronavirus spurred immune responses in healthy adults given the shot in an early-stage study, a hint that the experimental candidate could be working as intended.

The company offered little supporting data for its claim, indicating only that neutralizing antibodies to SARS-CoV-2 were found in more than 90% of study participants tested two weeks after inoculation. Importantly, no serious side effects occurred among the more than 700 volunteers enrolled in the trial, according to Sinovac. 

Results from the Phase 1/2 study, which Sinovac conducted in the Jiangsu province of China, will be published in a medical journal, the company said. So far, only one company — China's CanSino Biologics — has detailed coronavirus vaccine study data in an academic publication.  

Sinovac's announcement, roughly three weeks after CanSino's data were published, reflects the quick pace of coronavirus vaccine research in China, which is host to at least three other research programs now in human testing.

Sinovac, which sells several influenza and hepatitis vaccines in China, started the Phase 1/2 test of its vaccine on April 16, about a month after CanSino's entered clinical testing. After enrolling 143 healthy volunteers in the Phase 1 portion of the study, Sinovac enrolled another 600 into Phase 2. 

Participants were inoculated twice, on the first day and then again at two weeks. After another 14 days, Sinovac measured levels of neutralizing antibodies, immune proteins which are capable of preventing SARS-CoV-2 from binding to and entering human cells. 

While Sinovac said the rate of seroconversion, or when antibodies become detectable, was "above 90%" in Phase 2, there was little additional information to evaluate what that might mean. Scientists are still unsure what level of antibodies is needed to protect against infection, for example.

It's also not clear whether Sinovac has antibody data from all 600 participants in the Phase 2 portion of the study, or only from a subset. 

Moderna, the Cambridge, Massachusetts-based biotech that's been at the forefront of coronavirus vaccine testing in the U.S., also kept its first data disclosure brief, spurring criticism it boosted its share price without divulging necessary information to fully assess its claims. 

Sinovac's research effort is supported, however, by publication in Science of preclinical testing data from mice and monkeys. A draft manuscript of preclinical research conducted by the U.S. National Institutes of Health on Moderna's candidate was last week made available on the preprint server bioRxiv.

Unlike CanSino and Moderna, which are both using newer, less proven vaccine technologies, Sinovac's candidate is an inactivated vaccine, meaning a live virus is grown in cells and then chemically rendered ineffective. A number of vaccines for other infectious diseases, like influenza, mumps, or measles, use this approach. 

But, because the virus is inactivated, immune responses to vaccination aren't always strong. As a way around this, vaccine developers sometimes add an "adjuvant," which helps to boost the body's immune response. In April, Sinovac reached an agreement with Emeryville, California-based Dynavax to use an adjuvant contained in the company's hepatitis B vaccine approved in the U.S. 

Sinovac said it would begin planning for a Phase 3 study of its candidate. But testing likely won't happen in China, which has seen new infections drop significantly. Instead, Sinovac recently signed a deal with a Brazilian company to conduct a Phase 3 trial there. 

If testing proves Sinovac's vaccine successful, the company is preparing to be able to make up to 100 million doses annually at a site in China it's now building

Author:Ned Pagliarulo

Published: June 15, 2020

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