China has rolled out second boosters for those aged 60 and over or with weak immune systems, as the country braces for massive upticks in cases following a major policy shift away from zero-Covid last week. Health authorities said priority would be given to heterologous boosting programmes – a mix-and-match approach of second boosters that are different from the primary vaccine shots or the first booster. Several new vaccines, including the inhaled variety from CanSino Biologics and a nasal spray co-developed by the University of Hong Kong, Xiamen University and Beijing Wantai Biological Pharmacy, have been included in the second booster programme for those who received three inactivated vaccines – which is most of the Chinese population. The advised time gap between the first and second boosters is six months. This comes with the highly transmissive Omicron variant and its many offshoots expected to sweep through the population after China eased the key components of its zero-Covid policy of lockdowns, mass testing and compulsory quarantine. Protecting high-risk populations like the elderly, especially those aged above 80, is a major concern. Data from other countries that relaxed Covid restrictions show most deaths occurred among the unvaccinated over-60s, with those above 80 years old the hardest hit. But vaccination rates are significantly low among the elderly in China. According to official data released on Wednesday, more than two-thirds of over-80s and about 30 per cent of those above 60 years had yet to receive their first booster shot. Data from Hong Kong, which tackled a deadly Omicron wave in the spring, is being used by many analysts as a proxy to make forecasts about mainland China’s epidemiological trajectory following the easing of zero-Covid. What awaits China as zero-Covid is eased? Hong Kong seen to offer deadly clue Over 95 per cent of the Covid-related deaths in Hong Kong’s fifth wave were people aged over 60. For over-80s, the case fatality rate – that is, the number of deaths among confirmed cases – was 14.6 per cent for the unvaccinated, but under 4 per cent for those who had received two doses. For those with one booster dose, the rate dropped further – to 1.71 per cent. Israel in January became the first country to roll out second boosters for the elderly and vulnerable, with many Western nations following suit. In August, a World Health Organization expert group also advised second boosters for vulnerable groups like the elderly, to fortify their immune system as vaccine effectiveness waned after a few months. As for younger age groups with no underlying conditions, three doses should offer enough protection, many scientists believe. In China, most people have received two to three doses of domestically made Sinovac or Sinopharm inactivated vaccines, developed to fight the original strain of the Sars-CoV-2 coronavirus that causes Covid-19. But the protection offered by inactivated vaccines as a booster drops significantly after three months, studies show. Studies in Chile and Brazil have shown that mixing and matching different types of boosters – such as mRNA vaccines for recipients of two doses of inactivated vaccine – works better in boosting immunity than three doses of inactivated vaccine. Chinese mRNA booster fights Omicron 4 times better than Sinovac: study Repeatedly administering the same vaccine, on the other hand, could prove counterproductive, a study has shown. The study by China’s Sun Yat-sen University, published in peer-reviewed journal Nature in November, showed that a fourth dose of Sinopharm did not induce higher levels of antibodies against Omicron. The immune response cannot be endlessly boosted and a “turning point” or plateau would occur after repeated use, the researchers said. A third dose was the “turning point”, showed their study, carried out on a group of healthcare workers in the southern city of Guangzhou. Updated vaccines that specifically target the new prevailing variants of concern would be more effective as the second booster, the study suggested. China has been pushing for different options for booster shots. Recipients of three inactivated doses have several options to choose from for the second boosters programme just rolled out. These include CanSino’s viral vectored vaccine; recombinant protein vaccines from Zhifei Longcom, Zhuhai Livzon, Chengdu Westvac or Clover Biopharma, as well as the one from SinoCellTech based on the alpha and beta variants; and the CanSino and Beijing Wantai vaccines targeting mucosal surfaces. China has yet to approve any mRNA vaccines for its citizens, but recombinant protein vaccines are known for their safety and efficacy though they take more time to develop, such as the jab developed by US biotech giant Novavax – approved for initial vaccine regimens or homologous boosting by countries including the United States, Canada, Switzerland, France and Australia.