BEIJING, China: China's top disease control official says the country's coronavirus vaccine has a low rate of effectiveness and the government is considering mixing the Chinese vaccine with other brands to boost its strength.

Chinese vaccines "don't have very high protection rates," said Gao Fu, director of the China Centers for Disease Control, during a conference in the city of Chengdu.

Beijing has delivered hundreds of millions of vaccine doses abroad, while simultaneously questioning the effectiveness of the Pfizer-BioNTech vaccine.

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

While officials did not respond directly to Gao's comment, another China Centers for Disease Control official said developers are working on Chinese mRNA-based vaccines.

"The mRNA vaccines developed in our country have also entered the clinical trial stage," said the official, Wang Huaqing. However, he gave no date as to when this vaccine might become available.

Vaccines made by Sinovac, a private company, and Sinopharm, a state-owned firm, have been shipped to several dozen countries, including Mexico, Turkey, Indonesia, Hungary, Brazil and Turkey.

However, researchers in Brazil found the Sinovac vaccine was effective in stopping the spread of coronavirus in 50.4 percent of those vaccinated, compared to the Pfizer-BioNTech vaccine , which has been found to be 97 percent effective.

Chinese vaccines are unlikely to be sold to the United States, Western Europe and Japan, according to health officials.

According to Gao, some 34 million people in China have received both doses required for Chinese vaccines, while some 65 million received one.