The COVID-19 vaccines currently in use in China are effective against the Delta variant, which has become the globally dominant strain, spreading to over 130 countries, a health official said at a press briefing on Thursday.

Studies and epidemic prevention and control experiences show that the biological characteristics of the Delta variant do not have subversive changes compared with the original strain of the virus, said He Qinghua, an official with the National Health Commission (NHC).

The vaccines currently in use still offer sound preventive and protective effects, which can reduce the transmission of the virus and effectively lower the incidence of severe illness and mortality after infections, he said.

Last week, China's top epidemiologist Zhong Nanshan echoed similar observations, terming Chinese vaccines' effectiveness in reducing the risk of symptomatic and severe cases caused by Delta. Zhong's comments are based on a preliminary study during a COVID-19 flare-up in South China's Guangzhou City in May, where the country's first cases of the Delta variant were found.

Chinese vaccines are 100 percent protective against severe cases, the study said. Vaccines' effectiveness against moderate cases, mild cases and asymptomatic infections were 76.9 percent, 67.2 percent and 63.2 percent protective, respectively, Zhong said. The final findings of the study will be published later, he added.

He also noted 13 severe cases during the outbreak in Guangzhou in May, all of them unvaccinated.

The expert said China needs to inoculate 83.3 percent of the total population to achieve herd immunity.

As of Tuesday, over 1.7 billion doses of COVID-19 vaccines had been administered in the country.