The drugmaker behind one of China’s most promising coronavirus vaccine candidates is in talks to conduct late-stage trials globally as the race for immunization against Covid-19 intensifies.Beijing-based Sinovac Biotech Ltd. is in discussion with regulators in other countries, and the World Health Organization, to launch phase III clinical trials in regions where the novel coronavirus is still spreading rapidly, CEO Yin Weidong said in an interview Thursday.

“To evaluate whether the vaccine can give protection, we need to study the relation between disease incidence and vaccination,” Yin said. “You can’t do that when there’s no cases.”

With China having largely curbed its growth of new infections, its drugmakers will need to seek international cooperation to test their vaccine candidates in other countries — a task that may be complicated by tensions between China and some nations, especially the U.S., over how and where the virus originated.

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Sinovac is one of three Chinese companies at the forefront of efforts to halt a pandemic that’s sickened over 3.8 million people worldwide and killed nearly 270,000. While there are over 100 vaccines in development globally, only around 10 have reached the crucial final stage of human testing.

A working vaccine is the best hope for countries to re-open their suffering economies and resume normal life without a surge in cases. But vaccines typically take years to develop and still do not exist for many diseases, like HIV.

While declining to specify which countries they plan to hold trials in, Sinovac’s Yin hinted that the U.S. is an ideal location. “The U.S. has the most developed biotech industry, the most sophisticated regulatory framework and its epidemic is now the worst,” he said.

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American drugmakers like Moderna Inc. also have vaccine candidates in human trials, as do researchers from Oxford University. Johnson & Johnson is likely to start human trials in September. Besides Sinovac’s candidate, Chinese scientists have three others in human trials: one from the Chinese military in collaboration with Tianjin-based CanSino Biologics Inc., and two from state-owned China National Biotec Group Co.

CanSino’s effort also has plans to go global: the company submitted an application last month to conduct clinical trials for its vaccine in Canada.

Phase III Challenge

Most of the leading efforts are now in the midst of phase I and II of clinical trials, where experimental vaccines are administered to hundreds of healthy individuals to see whether they’re safe and can elicit an immune response.

It’s phase III — involving a control group of individuals who receive placebos or remain unvaccinated — that shows if those who have received the vaccine are able to steer clear of infection more than those who did not. This requires both groups, the vaccinated and the control, to be in an environment where the virus is still spreading.“The real challenge lies in the phase III trial,” Ding Sheng, director at the Global Health Drug Discovery Institute at Tsinghua University, said. “It will tell whether the immune response indicated in early trials can really be effective.”

Sinovac previously developed a vaccine against SARS, the 2003 pandemic caused by a close cousin of the coronavirus. The company had to stop development at the phase I stage as that outbreak, which sickened 8,000 people, came under control.

“We’ve got the vaccine ready,” Yin said. “Once any country approves the clinical trial, we will launch it immediately.”