BEIJING (REUTERS) - Sinovac Biotech's Covid-19 vaccine has been approved by China for emergency use in people aged between three and 17, its chairman Yin Weidong told state TV late on Friday (June 4).

The country's mass inoculation drive, which administered 723.5 million doses as of June 3, is currently open only to those 18 and above.

When Sinovac's shot will be offered to younger groups depends on health authorities formulating China's vaccination strategies, Mr Yin said.

He added that minors have lower priority for jabs compared with the elderly, who face higher risk of severe symptoms after infection.

Preliminary results from phases one and two of clinical trials showed the vaccine could trigger immune response in participants aged three to 17, and most adverse reactions were mild.

State-backed drugmaker Sinopharm, which has two shots using similar technology to Sinovac's product, is also submitting data for clearance in younger groups. A vaccine from CanSino Biologics, adopting a different technique, has entered a phase two trial involving those aged between six and 17.

Sinovac has also completed a phase two trial where participants were injected with a third booster dose after completing two regular shots, Mr Yin said.

Participants saw a tenfold increase in antibody levels compared with previous levels in a week, and 20-fold in half a month, he added.

He cautioned that Sinovac still needs to complete longer-term observation of antibody duration before it can make a recommendation to authorities about when a third dose should be given.