A Chinese study looking at mixing Covid-19 vaccines showed that receiving a booster shot of CanSino Biologics' vaccine after one or two doses of Sinovac Biotech's vaccine yielded a much stronger antibody response than using the Sinovac shot as a booster.

The study, among the first analyses in China combing different Covid-19 vaccines, comes as the country said it would use booster shots in specific groups amid concerns over vaccines' waning protection over time.

Participants who received a CanSinoBio booster dose three to six months after a second Sinovac shot showed a...