Hundreds of thousands of Chinese have been given two experimental Covid-19 vaccines under an emergency scheme without a single case of infection, a top official with a state-owned vaccine developer has said.

Zhou Song, secretary for the commission for discipline inspection with China National Biotec Group, also said the company’s two candidate vaccines were likely to protect people for up to three years.

Zhou told China National Radio on Monday that the firm’s vaccines were the most widely used in the emergency scheme, adding: “Hundreds of thousands have taken the shot and no one has shown any obvious adverse effects or got infected.”

CNBG’s two vaccines are still undergoing phase three trials for safety and efficacy in several countries, including the United Arab Emirates, Bahrain, Peru, Morocco, Argentina and Jordan.

China’s emergency vaccine scheme began in late July and allows high-risk groups – including health care workers, diplomats and people who work abroad – to receive vaccines that have not yet been approved by regulators.

Zhou said that this group included tens of thousands of people who work overseas adding that the lack of infections “proves the effectiveness of the vaccines”.

Eight vaccines are currently undergoing phase three trials around the world, including four made by Chinese companies.

Three of the Chinese vaccines – including the two made by CNBG and one developed by Beijing based Sinovac-have been approved for emergency civilian use, while a fourth has been given the greenlight for use by the military.

Sinovac’s product is currently being tested in Brazil and Indonesia and the trial is expected to expand to more countries. The company has reportedly said that tens of thousands of people have already been given the vaccine under China’s emergency use scheme.

Meanwhile, the Chinese military has given the green light to the limited use of a candidate vaccine developed by CanSino and the Academy of Military Medical Sciences.

Yu Xuefeng, chairman of Tianjin-based CanSino Biologics, told state broadcaster China Central Television that those who needed the vaccine included troops “on peacekeeping missions in countries and regions where Covid-19 has yet to be put under control”. He did not say how many people had been given the vaccine.

CNBG’s vaccines have also been offered to employees of some businesses. Last week the pharmaceutical company announced that it had signed a deal with telecoms giant Huawei to offer vaccines and other treatments to employees.

The news website Caixin has also reported that an unnamed state-owned company in Beijing has also been offering its staff a vaccine since June, a month before the emergency use scheme started.

The report also said that the company – which operates in more than 30 countries – had asked all employees who have to travel overseas to take the injections and quoted one employee as saying that hundreds of people had agreed to do so.

Caixin also reported the Civil Aviation Administration of China has urged airline workers to take one of the candidate vaccines.

On Monday, Zhou dismissed suggestions that the vaccines might only offer protection for short periods.

The Covid-19 candidates were first tested on 180 senior executives and officials of CNBG’s parent company, the China National Pharmaceutical Group, also known as Sinopharm.

Zhou said they still showed high levels of antibodies, and added: “At present, based on the results of animal experiments, phased research results, and similar vaccines using similar technology, it is without question that immunity can last from one to three years.”

He also said it looks unnecessary to take annual shots like flu shots and the vaccine has covered the current known mutations of the coronavirus that causes Covid-19.

“There are indeed several subtypes of the virus that are mutating, but its main gene sequence and protein level has not fundamentally changed. The inactivated vaccine will have no problem in dealing with these mutated viruses in the next few years and can cover them,” Zhou said.

CNBG has built two secure facilities in Beijing and Wuhan to produce the vaccines. He said the annual production capacity of more than 220 million doses will rise to between 800 million to one billion when work to extend the facilities is complete.