China and Russia appear poised to sell their own COVID-19 vaccines to countries desperate to vaccinate their population but without the financial resources to buy U.S. vaccines. However, healthcare experts have expressed growing concerns over the efficacy and safety of these candidates.

Wealthier nations have purchased preliminary doses of the Pfizer and Moderna vaccines, which were given emergency use authorization by the U.S. Food and Drug Administration that painstakingly reviewed the clinical data of their trials, including the crucial Phase 3 trials. According to the Centers for Disease Control and Prevention, in Phase 3 trials, the vaccine is given to thousands of people and tested for efficacy and safety.

According to The Washington Post, Chinese and Russian firms are projected to be among global vaccine production leaders in 2021. Naor Bar-Zeev, an expert on international health and disease epidemiology at the Johns Hopkins Bloomberg School of Public Health, told the Post “The idea that the Russians and Chinese are just not as good at this as we are is just vaccine nationalism. There’s no reason to think these vaccines don’t work. But we have not seen Phase 3.”

One country, Cambodia, has not requested the Chinese vaccine candidate from the biotech firm Sinovac because Prime Minister Hun Sen said the drug has not been approved by a global body. But the United Arab Emirates did approve the Sinopharm vaccine after reviewing the Chinese data that revealed the vaccine was 86% effective. Other countries followed suit, according to the Post.

Developers of Russia’s Sputnik V vaccine recently announced they will share their vaccine info with pharmaceutical giant AstraZeneca in the first collaboration of labs to advance the vaccine race. Argentina has said it will buy the Sputnik V vaccine.

Healthcare experts said they would feel more comfortable if the Phase 3 trials results from Russia, China, and now Iran, that recently announced it is also developing its own vaccine, were more available and transparent. Iran, the hardest hit nation by COVID-19 in the Middle East, created its own homegrown vaccine because their leader expressed his mistrust of a vaccine developed by foreign powers, according to The Independent.

However, experts said the bottom line on vaccine efficacy and safety is the data revealed in well controlled clinical trials. And until that data is reviewed by an international health organization, the jury on foreign COVID-19 vaccines remains out.

“It’s all tied to the results of Phase 3,” said Jennifer Huang Bouey, an epidemiologist at the Department of International Health at Georgetown University, according to the Post. “We haven’t seen anything yet.”

In the meantime, the Sinovac vaccine has already been shipped to countries like Brazil and Indonesia which may force their governments to approve its use.

Bar-Zeev told the Post that if countries continue to distribute vaccines overseas, they will most likely need to be reviewed and approved by the World Health Organization, which may ease fears from those who doubt their efficacy and security.

“It will get reviewed as all products get reviewed,” he said. “And will need to pass that bar before WHO would support its widespread use.”