(CBS News) – China has been administering experimental coronavirus vaccines to large numbers of workers deemed to be at high risk of exposure to the virus for more than a month, a senior health official confirmed over the weekend. Among those getting doses of unproven vaccines are frontline health workers, public service workers and border officials, but the government has not said which trial vaccine or vaccines they’re getting, or how many have had it. Zheng Zhongwei, director of the Development Center for Medical Science and Technology at the National Health Commission, said in an interview with State Broadcaster CCTV Saturday night that the government had authorized the emergency use of vaccines developed by domestic companies on July 22. Zheng, who also heads China’s coronavirus vaccine development task force, said the emergency use authorization was in line with the Chinese vaccine management law, which allows unapproved vaccine candidates to be used on people who are at high risk of infection for a limited period. Zheng said the emergency provisions could be expanded to include more groups of people, “to better prepare for a possible next wave [of infections] in autumn and winter.” He said the NHC had approved high-level production at a facility run by the China National Biotec Group (CNBG), the biological product arm of the government-owned pharmaceuticals company Sinopharm. Even before the emergency use was authorized, China’s military in June approved the use of a vaccine being developed jointly by another Chinese vaccine maker, CanSino, and the Academy of Military Science. Russia, Pakistan, and Saudi Arabia have agreed to conduct final stage trials for CanSino’s candidate vaccine. FDA issues emergency authorization for COVID-19 treatment State media said in June that employees at state-owned enterprises could volunteer to take one of two vaccine candidates being developed by CNBG before travelling overseas. But the government didn’t share information on the experimentation with other nations and last week Chinese mine workers who had been given doses were barred from entering Papua New Guinea. Inside a Phase 3 COVID-19 vaccine trial 04:56 Despite the limited information provided by officials on the “emergency” use of the vaccines, there has been little concern voiced publicly by Chinese citizens, including by those given doses. A few commenters on Chinese social media platforms asked why the government had waited a month to announce the program, but many voiced support and thanked those in high risk groups for taking part. Others wondered when other groups, including college students, might be able to get the jabs. One employee at a state-owned company wrote on the Twitter-like platform Weibo that she was given a trial vaccine due to her risk of interaction with travelers from overseas, and that “two thirds of my colleagues felt dizzy like me after the injection, but no fever or any other symptoms.” A security guard stands in front of a building of China’s vaccine specialist CanSino Biologics Inc, in Tianjin, as work progresses on a candidate coronavirus disease (COVID-19) vaccine, August 17, 2020.THOMAS PETER/REUTERS She said she was given an “inactivated vaccine” — one made using coronavirus cells that have been killed, rather than live virus. Three of China’s candidate vaccines are of the inactivated type, which are sometimes found to provide less long-lasting immunity, and thus may require multiple doses. Both of the vaccines being developed by CNBG are inactivated. Separately, a nurse from a hospital in the northern city of Jinan said online that she felt thirsty and sleepy after her injection, but experienced no other reactions. Four of the seven candidate vaccines that have entered phase-3 human trials around the world are from China. Two of them are being developed by CNBG. In addition to the doses given in China, the state-owned company has been approved to carry out trials of its vaccines in the United Arab Emirates, Bahrain, Peru, Morocco and Argentina. Chairman Yang Xiaoming has said that 20,000 people have taken part in the overseas trials, and that preliminary results have been positive. Beijing-based Sinovac is developing the other candidate vaccine, with help from Indonesia and Brazil to run phase-3 trials. The company has vowed to provide its vaccine, once proven safe and effective, to countries with high infection rates, with an expected capacity to produce of 300 million doses per year, according to Sinovac chairman Yin Weidong.