Chinese vaccines "don't have very high protection rates", said Gao Fu, director of the China Centres for Disease Control, in a rare admission at a conference in the southwestern city of Chengdu on Saturday.

Beijing has distributed hundreds of millions of doses to 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 immunisation 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 per cent by researchers in Brazil.

By comparison, the vaccine made by Pfizer has been found to be 97 per cent effective.

Beijing has yet to approve any foreign vaccines for use in China, where the coronavirus emerged in late 2019.

Gao gave no details of possible changes in strategy but mentioned mRNA, a previously experimental technique used in the fight against COVID-19 by Western vaccine developers while China's drug makers used traditional technology.

"Everyone should consider the benefits mRNA vaccines can bring for humanity," he said.

"We must follow it carefully and not ignore it just because we have several types of vaccines already."

Gao has previously raised questions about the safety of mRNA vaccines. He was quoted by the official Xinhua News Agency in December as saying he could not rule out negative side-effects because they were being used on healthy people for the first time.

Chinese state media, as well as popular health and science blogs, have also questioned the safety and effectiveness of the Pfizer vaccine, which uses mRNA.

As of April 2, some 34 million people had received both of the required doses of Chinese vaccines and about 65 million had received one, according to Gao.

Australian Associated Press