In a rare admission of the weakness of Chinese coronavirus vaccines, the country’s top disease control official says their effectiveness is low and the government is considering mixing them to give them a boost.

Chinese vaccines “don’t have very high protection rates,” said the director of the China Centers for Disease Control, Gao Fu, at a conference on  Saturday in the southwestern city of Chengdu.

Beijing has distributed hundreds of millions of doses in other countries while also trying to promote doubt about the effectiveness of Western vaccines.

“It’s now under formal consideration whether we should use different vaccines from different technical lines for the immunization process,” Gao said.

The effectiveness rate of a coronavirus vaccine from Sinovac, a Chinese developer, at preventing symptomatic infections has been found to be as low as 50.4 percent by researchers in Brazil. By comparison, the vaccine made by Pfizer has been found to be 97 percent effective.