Many mainland Chinese cities started rolling out Covid-19 booster shots for the public last week as immunity wanes. Over 75 per cent of the 1.4 billion population is now fully vaccinated, but the jabs have been available in China since the second half of last year – meaning many people had them more than six months ago. For the Chinese vaccines , immune response can fall below the minimum threshold after six months. As people get their third jabs, the level of neutralising antibodies they induce will be closely watched. Trials show that boosters can significantly raise that level, but the question is how long the immunity will last. Inactivated vaccines are the most common in China, and it is still holding back on approving BioNTech’s mRNA jab that is widely used in the West. The reason has not been made public, but trial results are pending for Chinese experimental vaccines using mRNA technology – those made by Walvax Biotechnology and Suzhou Abogen Biosciences are reportedly expected to be available by the end of the year. Chinese experts have said the country would consider reopening once 85 per cent of the population was fully vaccinated, but with herd immunity now an elusive target as the jabs become less effective, the country’s tough virus control measures could continue. Elsewhere, countries with high vaccination rates are facing challenges as they try to live with the virus. Although vaccination has been shown to significantly reduce death rates, Singapore has seen a much higher number of deaths than before it opened up. Most of those who have died were aged over 60 and more than half were unvaccinated, but low immunity among the elderly is also a factor. In Britain, where over 67.8 per cent of the population is fully vaccinated and restrictions have been lifted, daily cases topped 50,000 last week with 200 deaths per day. Some are blaming the latest surge on transmissions in schools and a lack of willingness to reimpose social distancing measures. Scientists have always warned that vaccines would not be a silver bullet, and that public health measures would be needed even with mass immunisation. We now see two extremes: China keeping its borders tightly shut, the holdout on “Covid zero”, while other countries with high vaccination rates pay a human cost for reopening. All nations will eventually have to learn to live with this virus in a rational way, through both vaccination and mitigation measures, including, if it is developed, an effective treatment.