The suspects had been carrying out the ruse since at least September last year, Xinhua said on Monday, adding that all fake doses had been tracked down.

The fake vaccines were made by injecting saline into syringes, it said. The suspects may have intended to send the vaccines abroad, the government-backed Global Times newspaper reported, citing a source close to a major Chinese vaccine producer.

The police operation was carried out by police in multiple places including Beijing, Shanghai and the eastern province of Shandong, Xinhua said.

Countries around the world from have been rolling out vaccine programmes in the hope of bringing the year-long coronavirus pandemic to an end.

Earlier on Monday, a World Health Organization-led team investigating the origins of the COVID-19 pandemic was due on Monday to visit the Center for Disease Control and Prevention of Hubei province, the central Chinese region where the outbreak emerged in late 2019.

The group of independent experts left two weeks of quarantine on Thursday in Wuhan, the capital of Hubei province, and is conducting two weeks of field work. So far, it has included visits to hospitals, markets, and an exhibition commemorating Wuhan's battle with the outbreak.

The WHO, which has sought to manage expectations for the mission, has said that team members would be limited to visits organised by their Chinese hosts and would not have any contact with community members, because of health restrictions.

No full itinerary for the group's field work has been announced, and journalists covering the tightly controlled visit have been kept at a distance from team members.

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