China has fully inoculated two-thirds of its population with coronavirus vaccines as the country races to build an immunity barrier . The National Health Commission’s disease control bureau said that by Monday, 960 million people, or 67 per cent of the population, had completed their doses. In all, 2.11 billion doses had been administered, meaning 1.09 billion people, or 77.6 per cent of the population, had been given at least one shot, according to Wu Liangyou, the bureau’s deputy head. “Overall vaccination of 12-17 year-olds is also progressing quite well, with 162.28 million doses administered so far,” Wu said on Tuesday. Public health experts such as respiratory disease specialist Zhong Nanshan have said that at least 80 per cent of the population would have to be vaccinated to reach herd immunity – when community outbreaks are very limited. While China is on track to reach that target, variants of the coronavirus could pose a threat and vaccine developers around the world are looking to update their formulas from the original ancestral strain. Zheng Zhongwei, director of the NHC’s Development Centre for Medical Science and Technology, said precautions were being taken in China to update vaccines for variants even though mutations in the coronavirus had so far been relatively stable and existing vaccines were effective against all variants. Last week the World Health Organization listed the Mu variant, or B.1.621 , as the fifth one of concern since the agency started noting variants that are more contagious, cause more serious illness, or show signs of possible resistance to vaccines. While the global prevalence of Mu among sequenced Covid-19 cases is below 0.1 per cent, its prevalence has consistently increased in Ecuador and Colombia, where it was first detected in January. Mu has a number of mutations that suggest it could be more resistant to vaccines, but the WHO said further research would be needed to confirm it. Zheng said updated Covid-19 vaccines in China would still need to be subject to preclinical studies and human clinical trials. The regulatory authority is drafting a guideline on reviewing and approving vaccines targeting variants. Some inactivated vaccine developers have carried out research on vaccines for the Gamma and Delta variants and completed preclinical studies. The developers have applied for clinical trials with the Centre for Drug Evaluation, according to Zheng. China has approved three inactivated vaccines for general use with conditions and two others for emergency use. Some developers of recombinant protein-based vaccines have designed broad-spectrum or polyvalent vaccines against different variants, with some in rolling application for clinical trials. Zheng said China had given emergency use approval to one protein-based Covid-19 vaccine while eight others were at different stages of clinical trials. Developers of adenovirus-vectored vaccines and mRNA-platformed vaccines were also working on jabs against Beta and Delta variants and had completed animal efficacy and safety experiments, Zheng added. “With such preparations, even if a serious mutation of the virus occurs in the future and completely escapes the preventive effects of the vaccine that are in production, we will be able to quickly develop and produce new vaccines on a large scale,” he said. “We are well prepared.” Zheng said inactivated vaccines, the most commonly used ones in China, still worked well on the Delta variant, with real world data showing they could prevent infection to a certain degree, achieve a clear effect on blocking transmission after infection and have a significant effect on preventing severe illness and death, even “when variants, especially the Delta variant, are prevalent”.