China's COVID-19 vaccines are effective against the two major variants of the novel coronavirus that have been imported, but sustained efforts are still needed to prevent other strains from entering, the Chinese Center for Disease Control and Prevention said.

Thirty-seven confirmed cases caused by the B.1.1.7 variant of the novel coronavirus, first identified in the United Kingdom, had been reported on the Chinese mainland by Feb 10. Another nine confirmed cases were caused by the 501Y.V2 variant, which was first detected in South Africa, the China CDC said.

There are no reported cases on the mainland of the P.1 strain first identified in Brazil and now circulating globally, the center said.

In addition to the three major variants of the novel coronavirus, new strains have been reported in the United States, Scotland and Germany, and research is underway on their infectiousness and toxicity.

"These variants have not been exported to China yet, and continued prevention and control efforts are needed to prevent them from entering," the China CDC said.

The COVID-19 outbreak in China has been kept under control since April, with the reopening of Wuhan, Hubei province, after a 76-day lockdown. However, importation of the virus via people and cold-chain goods remains a major risk.

Small scattered clusters of outbreaks have occurred across China since April, despite strict measures to stop the virus entering the country. All of them were quickly controlled.

The B.1.1.7 variant, which is up to 75 percent more infectious than previous strains, was first reported on the Chinese mainland in December after a student returned from the UK. Other imported cases of the variant were reported in Guangdong and Shandong provinces and Tianjin. It also caused a cluster of infections at a community in Beijing's Daxing district in January. In the same month, Guangdong's provincial CDC reported the first COVID-19 case in China of the 501Y.V2 variant.

"Various studies have shown that existing COVID-19 vaccines, including the inactivated vaccines in China, still provide good protection against the B.1.1.7 variant," the China CDC said. "The vaccines' protection against the 501Y.V2 variant is found to be diminished to some extent, but they are still effective."

Research on the efficacy of the vaccines to protect against the P.1 variant is underway, but they may be less effective due to mutations that are shared with the 501Y.V2 variant, the center said.

Despite a potential reduction in the efficacy of the vaccines to treat the variants, immunization is still the most effective measure to prevent infections, said Xu Wenbo, director of the China CDC's National Institute for Viral Disease Control and Prevention.

"Although receiving a vaccination reduces the risk of getting COVID-19, it does not mean the recipients will be entirely immune to SARS-CoV-2," he said. "People should continue …self-protection after receiving the vaccine, and they should also quarantine for medical observation if they have been in contact with confirmed COVID-19 cases."

The transmission of novel coronavirus variants poses a new challenge for prevention and control measures in China and there is no room for being lax, Xu said.

Existing epidemic prevention and control measures in China have proved effective in coping with the outbreaks caused by new variants. Individuals can minimize the risk of infection by following recommended procedures such as wearing masks, washing hands and practicing social distancing, he said.