RN Desk:hina’s top respiratory disease expert Zhong Nanshan has said the country could reach herd immunity against Covid-19 by the end of the year if more than 80% of the population is fully vaccinated, says South China Morning Post in a report.

He said while Covid-19 vaccines, including Chinese ones, are less effective six months after the first dose, herd immunity was still achievable with booster shots.

“[At this stage] we believe a booster shot could strengthen the efficacy of the vaccines and we estimate more than 80% of the population will be vaccinated by the end of this year. Therefore we hope that we will be able to achieve herd immunity [by then],” Zhong told a China-Arab states conference in the Ningxia Hui region via video link.

That forecast was based on data showing that Chinese vaccines had an average efficacy of around 70%, he said.

Zhong also cited a follow-up study on Sinovac’s early stage clinical trials that found a twentyfold increase in neutralising antibody levels– indicating immune response–in people who were given a third dose of the Sinovac jab, nine months after their second. In elderly people it went up 30 times.

A study published last month, co-led by Sinovac, found that a third dose of the vaccine given six or more months after the second jab could boost the concentration of antibodies by three to five times. Antibody levels were found to have declined substantially six months after two doses were given, but the study concluded that a third dose resulted in a “strong boost in immune response”. The research has not been peer-reviewed and was posted on preprint server medRxiv.org.

It comes as countries around the world are looking at whether third doses for those who have been immunised are needed. China has yet to announce a policy on booster shots, and it is not clear at what stage they might be given and whether vaccines could be mixed, something officials have said would be studied. Most people inoculated in China have received the inactivated vaccines made by Sinovac and Sinopharm. The medical products regulator last week approved clinical trials for the combined use of the Sinovac jab and a DNA vaccine developed by US biotech firm Inovio.

Other countries are also looking at mixing vaccines. Last week, Turkish researchers said a study of more than 30 million inoculated people found that three doses of inactivated vaccines offered more protection than receiving an mRNA vaccine booster shot after two inactivated vaccine doses.

Meanwhile, as the highly infectious Delta variant rages, countries including the United States and Israel – where people have mostly received mRNA vaccines – have recently approved booster shots.

On Friday, Zhong again said that Chinese vaccines still offered protection against the Delta strain, though they were not as effective. He cited a small study in Guangzhou during a Delta outbreak earlier this year that found the Chinese vaccines were 59% effective in preventing infection, and 70% effective in preventing moderate cases. No serious cases were found among the 74 vaccinated people in the study.

But Zhong did not comment on whether China could reopen its borders once herd immunity was reached. A zero-tolerance strategy has kept the virus largely under control in China, but some have questioned how sustainable it is. Former health minister Gao Qiang criticised those who suggested China should abandon the strategy and learn to live with the virus in an article in Communist Party mouthpiece People’s Daily on August 7. His comments prompted an online backlash against well-known epidemiologist Zhang Wenhong, who had earlier said China needed a long-term strategy to live with Covid-19 but did not say the country should reopen its borders.

On Wednesday, Zhang wrote on social media network Weibo that “we must hold on to the firm belief that the current pandemic coping strategy our country adopts is the most suitable for us by far”.