A medical staff administers a second booster dose of COVID-19 vaccine for an elder through nose at a temporary vaccination site in Haidian District, Beijing, capital of China, Dec. 17, 2022. China is continuing its optimization of COVID-19 epidemic prevention and control measures as it shifts the focus of its response strategy from curbing new infections to preventing and treating severe cases. On Wednesday, the government announced that it would offer a second booster dose of the COVID-19 vaccine to vulnerable groups who had received their first booster shot more than six months ago. (Xinhua/Ren Chao)

Is the second booster shot still necessary for people who have been infected with COVID-19? China's State Council joint epidemic prevention team said yes, calling on the public to choose a different vaccine from the previous three doses as their second booster shot.

The immunity triggered by COVID-19 infection alone will be less strong than the immunity generated by the virus infection plus receiving a second booster shot, said experts from China's State Council joint prevention and control mechanism against COVID-19 on Sunday while explaining questions of public concerns on the vaccination.

The joint team said those who have been infected by COVID-19 should receive the fourth shot at least six months after their infection, saying shots that used different technology (heterologous vaccines strategy), or provided cross immunity effect against the Omicron virus should be given priority.

If people took the inactivated vaccine as their previous shots, the fourth shot should not be an inactivated vaccine but one from different technology, emphasized Zeng Guang, a former chief epidemiologist from the Chinese Center for Disease Control and Prevention (CDC), in a speech about the reason and solution of the epidemic on Thursday.

The heterologous vaccines strategy aimed at stronger and better immune protection for people as studies from Sun Yat-sen University and from some foreign countries have shown that four shots of inactivated vaccine can only provided a very limited protection, Zhuang Shilihe, a Guangzhou-based medical expert, told the Global Times on Sunday.

"Many countries have used mRNA vaccines as booster. In China, we currently used the recombinant protein-based vaccines and the nasal spray influenza virus vector vaccines as booster," Zhuang said.

The joint team on Sunday also extended the availability of domestic COVID-19 vaccine (CHO Cell) produced by Anhui Zhifei Longcom Biopharmaceutical to people aged three or above, approving the vaccine as the first booster shot for adults who have completed two shots of the same vaccine six months prior.

China rolled out plan for COVID-19 second booster shot on December 14, which targeted people from high-risk groups, the elderly and those with underlying diseases and a weak immune system.

As of Sunday, multiple places across China have released the location of local vaccination sites and encouraged the public to get a second booster shot. 

People can check local vaccination sites and the vaccine's categories via the internet in cities including Beijing, Shanghai, Guangzhou and Shenzhen in South China's Guangdong, Hangzhou in East China's Zhejiang, Hohhot in North China's Inner Mongolia Autonomous Region, as well as places in Central China's Henan and Hubei, in East China's Shandong and Fujian and in Southwest China's Yunnan.

The joint team said the booster vaccination will evoke the body's immune memory cells and boost antibody levels to further consolidate the preventive effect against severe illness and death as antibody levels decrease over time after previous vaccination and weaken due to the virus' stronger immune evasion from mutation.

Zhuang said there should be a specific and detailed explanation on under what circumstances should people receive what kind of vaccines.