BEIJING, SEPTEMBER 7

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 78-fold jump on average in neutralizing antibody levels two weeks later, according to a paper published on Monday before a peer review.

By contrast, those who received a Sinovac booster shot showed a 15.2-fold increase in neutralizing antibody levels, researchers from local disease control authorities, CanSinoBIO and other Chinese institutions said in the paper.

One dose of Sinovac followed by a CanSinoBIO booster at intervals of one or two months led to a 25.7-fold increase in neutralising antibody levels, while two doses of Sinovac induced a 6.2-fold increase.

The study analysed data from about 300 healthy adults aged 18-59.

The study did not assess the boosters' protection against COVID-19 and did not test the neutralising antibody against the more transmissible Delta variant, the paper said.

More than 1.4 billion doses of the Sinovac vaccine have been administered globally, about three quarters of them in China.

China, which has kept local infections under control, has fully vaccinated around 69% of its population as of Sept. 6. It said on Tuesday a total of 2.1 billion doses had been administered as of Monday.