TAIPEI, Taiwan — Chinese vaccine makers are looking at mixing their jabs and whether a booster shot could help better protect against COVID-19.

Sinovac and Sinopharm, the two Chinese manufacturers that combined have exported hundreds of millions of doses all over the world, say they’re are considering combining their vaccines with those from other companies.

Earlier this month, the head of China’s Center for Disease Control, Gao Fu, said that current vaccines offer low protection against the coronavirus and mixing them is among strategies being considered to boost their effectiveness.

Gao later tried to walk back his comments, saying he was talking in general about improving vaccine efficacy.

China National Biotech Group has a plan for future “sequential use” of their vaccines, Li Meng, the head of international cooperation for the company, said Wednesday at an international conference.

The company, a subsidiary of state-owned Sinopharm, made two inactivated COVID-19 vaccines and a third in clinical trials.

Sinovac, a private company based in Beijing, also said they were in preliminary discussions with investigators, including China’s Center for Disease Control, about combining the doses of their vaccine, CoronaVac, with others.