BEIJING -- A total of 13 types of COVID-19 vaccines, approved for conditional marketing or emergency use, are now available as a second booster dose in China, according to experts with the State Council inter-agency task force for COVID-19 response.

Omicron-resistant vaccines are preferred in choosing second booster doses, said experts with the State Council joint prevention and control mechanism against COVID-19.

As of Friday, more than 3.46 billion COVID-19 vaccine doses had been administered on the Chinese mainland, with over 90 percent of the population fully vaccinated.

The level of antibodies will drop over time after vaccination, experts said, adding that virus mutations also lead to strengthened immune evasion, making antibodies less effective.

Studies show that getting a booster jab can activate the immunological memory cells in the subject's body and increase the antibody levels, so as to further consolidate the prevention of severe illness and death, experts said.

They suggested eligible people who have not received a booster shot should get one as soon as possible to get better protection against the virus.

Population groups with a high risk of infection, people aged 60 and above, people with serious underlying health conditions, and those with low immunity are advised to receive a second booster shot six months after the first one.

Those who have received three doses of inactivated vaccines can choose a different type of vaccine -- recommended by the government -- for the second booster, namely a recombinant protein vaccine, an adenovirus vector vaccine or an influenza virus vector vaccine, according to the experts.

The Chinese Center for Disease Control and Prevention has conducted monitoring of adverse reactions to COVID-19 vaccines based on over 3.4 billion inoculations administered to over 1.3 billion people.

The monitoring results showed that the incidence rate of adverse reactions to COVID-19 vaccines is similar to those of other common vaccines, and that the incidence rate of adverse reactions for the elderly is slightly lower than that of young people.