This week the Chinese vaccine maker Sinovac announced it will launch a Phase I and II clinical trial later this month to test its vaccine in over 500 children ages 3 to 17 in China. The trial will test both the safety of the vaccine and also examine whether it produces an immune response among the participants.

Experts say the need to conduct COVID-19 vaccine safety trials specifically among children is clear, but that holding the trials before a vaccine has been proved safe and effective among adults represents uncharted and ethically fraught territory.

CoronaVac

Sinovac’s vaccine candidate, called CoronaVac, is based on the most tried-and-tested approach to vaccine development: using an inactive version of COVID-19 to teach the immune system to build up tolerance against the disease.

After initiating development of the vaccine on Jan. 28, the company is now among the lead pack of companies in the global vaccine race and is one of nine vaccine makers globally to reach Phase III trials. The company is currently testing CoronaVac among thousands of participants in Brazil, Indonesia, and Bangladesh.

But Sinovac has also shown a willingness to eschew some normal safety procedures in deploying its vaccine.

The company is one of several Chinese vaccine makers involved in the country’s controversial emergency-use program, which has inoculated hundreds of thousands of Chinese citizens, including frontline medical workers and other select population groups, even though Phase III clinical trials—which are designed to prove a vaccine is effective as well as safe—have not been completed. In early September, Dr. Yin Weidong, chief executive of Sinovac, told Reuters that the company had already injected as many as 3,000 Sinovac employees and their families who are not part of the clinical trials.

Sinovac’s rushed and norm-breaking path may in part explain why it is willing to test its vaccine in children.

John Moore, a professor of microbiology and immunology at Cornell University’s Weill Cornell Medical College in New York City, said it is highly unusual to conduct pediatric trials before a vaccine had first been proved to be safe and effective in adults.

“You would normally gradually expand the trials into children only after it was shown to be something safe and effective in adults,” he said. He explained that getting Phase III results back would usually be a vaccine maker’s “first port of call” before considering trials on children, but that Sinovac’s decision was one of many examples in which drugmakers seem to have discarded the usual playbook in order to develop a COVID-19 vaccine at a record pace. “This is not normal times,” he said.

Children and vaccines

Sinovac published the results of Phase I and II trials—studies that are designed to show a medicine is safe—Aug. 10 in a non-peer-reviewed paper on the online health research repository MedRxiv. The studies involved 600 people between the ages of 18 and 59. The company said there had been no serious adverse reactions among any of those receiving the vaccine. Sinovac also reported that its Phase I and II trials proved safe specifically among elderly volunteers in China in preliminary results on Sept. 9.

This data alone would not generally be adequate to commence trials on children, experts said. Moore said it was possible Chinese regulators had additional safety information from Sinovac that has not yet been published. “You have to hope the Chinese regulators have a body of safety data on this vaccine,” he said. “You have to assume they have a serious body of safety data in adults but we’ve not seen it because it has not been published.”

Sinovac did not return Fortune’s request for comment on this article.

U.S. regulators will almost certainly require pediatric vaccine safety trials before approving any vaccine for use in children, according to Dr. Steven Joffe, a pediatric oncologist and professor of medical ethics and health policy at the University of Pennsylvania Medical School.

He said normally a research team would want to wait for large-scale Phase III trials to prove that the vaccine is effective and to be reasonably confident that researchers had picked up on any rarer safety problems that might only be identifiable after the vaccine had been given to thousands of people. But he also said that the urgency of the global pandemic could alter this calculus.

“It’s a delicate balance,” Joffe says. “If you wait for more definitive efficacy results in adults, it puts you a year behind in kids. But if you jump out ahead of the adult results, you risk exposing kids to a vaccine that doesn’t work and will never get rolled out in the market.”

This is why U.S. and European vaccine makers may not be far behind Sinovac in testing vaccines on children. American pharmaceutical giant Pfizer, for example, recently said it would expand its Phase III trials in the U.S. to include included participants as young as 16.

Meanwhile, researchers at the University of Oxford in England, who are developing a COVID-19 vaccine in partnership with pharmaceutical company AstraZeneca, said they had put off initial plans to conduct a trial of their vaccine in children in the U.K. this fall. “At present we are not recruiting under 18-year-olds” into the vaccine trials, a university spokesman said. “Whilst we do plan to run a trial in this age group, we first hope to generate evidence of the vaccine efficacy in adults.” It said strong evidence that children were far less likely to become seriously ill from COVID-19 led the researchers to prioritize clinical trials for adults, who would likely also receive any vaccine before children do.

Chinese skepticism

Sinovac had spoken of its desire to conduct vaccine safety trials in children as far back as April, says Yanzhong Huang, vaccine expert and senior fellow for global health at the Council on Foreign Relations.

By starting such trials so early, Sinovac may be aiming to boost domestic confidence in a Chinese-developed vaccine among a skeptical public, he says.

In the 2010s, a series of domestic scandals in China’s vaccine industry undermined public trust in the country’s efforts to produce a vaccine. In 2018, 60% of Chinese parents surveyed said they were considering having their children inoculated outside of China after a government regulator found that a major Chinese producer distributed 250,000 substandard doses of a vaccine for diphtheria, tetanus, and whooping cough.

Sinovac was not directly tied to any of China’s substandard vaccines, but the company has been prone to missteps. In 2017, a Beijing court ruled that China’s pharmaceutical regulator received improper payments from vaccine makers including Sinovac. This prompted U.S. regulators to freeze trading on Sinovac’s stock on Nasdaq, and Sinovac’s case remains tied up in U.S. courts.

Huang says that China’s rushed COVID-19 vaccine development process is once again raising concerns about the safety and efficacy of Chinese-made vaccines and the reliability of government released information. Such pressure may help explain why Sinovac is motivated to prove as soon as possible that its vaccine is safe in children.

In China, there is a “growing critique of China’s approach to vaccine development,” Huang says. Such skepticism is why trials with children “may help boost public trust in Chinese-made vaccines.”