China is advancing the development of COVID-19 vaccines against variants and no evidence has proven that the current inactivated vaccines applied in the country were ineffective against the variants, experts said.

Zhang Yuntao, vice-president of China National Biotech Group, a unit affiliated with State-owned pharmaceutical giant Sinopharm, which developed two of China's three inactivated candidates, said at a news conference on Sunday that researchers have been continuously testing the anti-viral-mutation ability of those inactivated vaccines marketed across the country.

By using sera from phase II and III clinical trials in China and overseas, researchers have conducted numerous cross-neutralization experiments on a dozen strains, including those found in South Africa and the UK, and discovered that the antibodies produced by the two inactivated vaccines have demonstrated good neutralizing effect on all the tested strains, he said, adding that such experiments are still underway on strains found in Brazil and Zimbabwe.

He said mutations in the virus will always occur and cannot be prevented, but a small mutation without producing protective antigens will not alter the effectiveness of vaccines.

Various COVID-19 variants have been identified since late last year. Some of the new strains include those discovered in the UK, South Africa and Brazil and, although no evidence has proved that they would cause more severe illness for the majority of infected people, they were found to be much more contagious.

Gao Qiang, an executive at Sinovac Biotech, which developed the other inactivated vaccine, also told the conference that the company has already started the research and development of vaccines against the South Africa and Brazil variants.

Based on earlier cross-neutralization research on mutated strains found in 10 countries, their vaccine has proven to be effective, he said.

Despite the mutations, the two executives both said they have already earned rich experience in vaccine research and development and will be able to respond quickly and effectively to mutant strains.