BEIJING--China has been giving experimental coronavirus vaccines to groups facing high infection risks since July, a health official told state media.

No vaccine has yet passed final, large-scale trials to prove it is safe and effective enough to protect people from contracting the virus that has led to almost 800,000 deaths worldwide.

The aim is to boost the immunity of specific groups of people, including medical workers and those who work at food markets and in the transportation and service sectors, Zheng Zhongwei, a National Health Commission official, told state TV in an interview aired late on Saturday.

Authorities could consider modestly expanding the emergency use program to try to prevent possible outbreaks during the autumn and winter, added Zheng, who heads the Chinese government-led team that coordinates state resources for coronavirus vaccine development.

The guidelines for emergency use of potential coronavirus vaccines, approved on June 24 according to Zheng, have not been made public.

State media Global Times reported in June that China had been offering candidate coronavirus vaccines to employees at state-owned firms travelling overseas.

Some countries are skeptical about China's use of experimental vaccines. Papua New Guinea has denied entry to Chinese nationals who participated in a coronavirus vaccine trial, according to the Australian newspaper.

China's coronavirus vaccines will be priced close to cost, Zheng said.

"It does not mean that companies cannot make profits," Zheng said. "Companies should decide on moderate profits, or reasonable profits based on costs."

A potential coronavirus vaccine being developed by a unit of China National Pharmaceutical Group (Sinopharm) could cost no more than 1,000 yuan ($144) for two shots, Sinopharm chairman Liu Jingzhen told state media last week.

"(The price) will definitely be lower than what Liu said," Zheng said.