China's top epidemiologist Zhong Nanshan stressed the importance of receiving a booster shot after two doses of COVID-19 vaccine, at the Plenary Session of the 2021 Global Mayor's Forum in Guangzhou, south China's Guangdong Province, on Thursday.

"Whether people take the inactivated or mRNA vaccines, the humoral immunity decreased significantly in half a year after completing the vaccination course," Zhong said, as countries worldwide work to boost immunization.

Data showed that six months after the third dose, the geometric mean titer of neutralizing antibodies was higher than the peak of the second dose, both in 18-59 year-olds and people aged 60 and above, Zhong said.

For the booster shot of China's Sinovac, data released by Chile's Ministry of Health on October 7 showed that taking it after a full course of vaccination improved protection in symptomatic cases from 56 percent to 80 percent, and increased protection against hospitalization from 84 percent to 88 percent, Zhong added.

As of November 9, nearly 1.1 billion people in China had completed a full course of vaccination, with a vaccination rate of 75.8 percent, said Zhong, adding that 41.7 million had got a booster shot.

The expert said that the world will not be able to return to normal until the fatality rate decreases to about 0.1 percent and the reproduction number, known as R0, falls to 1.0-1.5. Achieving that will require whole-population vaccination to establish herd immunity, community mass prevention and the development of effective drugs.

And this will require worldwide efforts. "No country is safe until all countries are safe," said Zhong.