Renowned Chinese epidemiologist Zhong Nanshan has urged booster shots for the public to better guard against the COVID-19 epidemic, which has stricken many parts of the country since late October.

He also acknowledged the difficulty in striking a balance between economic development and epidemic intervention.

"Six months after a full dose of either whole inactivated virus or mRNA vaccine, antibody levels declined remarkably," Zhong said on Thursday evening at the 2021 Global Mayors' Forum held in Guangzhou, Guangdong province.

He shared the experiences of Guangzhou in fighting the epidemic in May, saying that Chinese COVID-19 vaccines are safe and effective, which has curbed the spread of the extra-contagious Delta variant in the city.

"None of the vaccinated patients had serious symptoms caused by Delta during the epidemic outbreak in Guangzhou in May," he said.

Guangzhou reported its first locally transmitted case on May 21 during the last round of the outbreak, which ended on June 18. The total number of infected people in the city was 159, according to official data.

"On one hand, it is necessary to restart the economy. On the other hand, we should control the epidemic," he said. "This requires precise prevention and control measures."

China reported 79 confirmed locally transmitted cases on Thursday, with more than half of them reported in Dalian, a port city in Liaoning province.

Dalian reported 52 locally transmitted cases on Thursday, increasing the total number of confirmed cases in the city to 135 since Nov 4.

Yi Qingtao, secretary-general of Dalian, said on Thursday that genome sequencing of the virus shows it was the Delta variant.

"This round of the outbreak in Dalian has characteristics of clusters in companies, families and schools," he said. "The virus is highly infectious and spreads quickly."

Among the 52 cases, 34 of them are university students.

The involved universities have suspended classes and all staff and students have taken nucleic acid tests.

Students are taking classes online in their dormitories at present.

Beijing has completed whole genome sequencing of the COVID-19 virus from the five confirmed locally transmitted cases that were reported on Thursday. The results showed that the genome is highly similar to the previous ones found in the capital, the Beijing Center for Disease Control and Prevention said on Friday.

Beijing reported six locally transmitted cases and one asymptomatic case on Thursday. Two were in Chaoyang district and five in Haidian. Many of the patients are employees of PetroChina, which is headquartered in the capital.