A senior Chinese health official has called on the World Health Organization to scrap late-stage human trials as a criterion for its coronavirus vaccine emergency use listing. The call comes days after a second Chinese Covid-19 vaccine was granted the listing. Zeng Yixin, vice-minister of the National Health Commission, said the WHO should consider replacing phase 3 human trials with data relating to neutralising antibody levels – an indicator of immunity – generated by the vaccines under consideration to scale up production. “We also advocate that the WHO make timely adjustments to the rules for listing emergency use for Covid-19 vaccines in light of the actual situation of global epidemic prevention and control,” Zeng was quoted as saying by state news agency Xinhua late on Sunday. “For vaccines with good results from animal trials, phase 1/2 clinical trials and the production in full compliance with good manufacturing standards, considerations should be made to exempt phase 3 clinical trials and using neutralising antibodies as an alternative indicator, and that could significantly increase the supplies of Covid-19 vaccines .” Two front runners in China’s Covid-19 vaccine response – inactivated vaccines by the Beijing subsidiary of Sinopharm and Sinovac Life Science – were listed by the WHO for emergency use on May 7 and June 1. Both vaccines were approved for emergency use in China with only phase I/2 human trials data last July and have been used to inoculate millions before being approved for general use with phase 3 data. Five more vaccines – including those by CanSino and Anhui Zhifei Longcom Biopharmaceuticals – are also applying for WHO emergency use listing. In the past, antibody levels in blood have been used to indicate vaccine effectiveness. For example, annual licensing of the seasonal flu vaccine booster is based on how well it generates a threshold of antibody levels. Researchers around the world are still studying immune “correlates of protection” that would preferably and reliably predict protection against Covid-19. China approves Covid-19 vaccine for children as young as three WHO experts met last month to discuss whether and how to move from clinical endpoint data to correlating measures of immunity. Experts say that such surrogate data can be used in bridging vaccines for additional groups, such as the elderly or adolescents, but a standardised substitute biomarker to evaluate the effectiveness of a new vaccine was needed since the data could vary between platforms of vaccine and even between vaccines within the same platform. Confidence in Covid-19 vaccines could be affected if a correlate that is not very rigorous was chosen or the vaccine did not work as well as expected, the meeting was told. Mainland researchers such as Zhu Fengcai, deputy director of the Jiangsu Centre for Disease Prevention and Control, have been studying to how to use surrogate endpoint data from immunity of Covid-19 vaccines that have released trials results to predict the protection of Covid-19 vaccines. In the early stage of the pandemic, China responded with vaccine development using different technologies starting as early as February last year, including the more advanced mRNA platform. China pushes to expand vaccine development with 20 candidates in trials But since China has now largely contained Covid-19, the country cannot test vaccines within its own borders and must instead conduct phase 3 trials overseas. This involves tens of thousands of participants and is a process described by industry insiders as long, expensive and challenging. Of the 21 Chinese vaccines at the human trials stage , eight, including the ones that have been approved for general use and have emergency use authorisation in China, are conducting human trials and one is in the process of overseas regulatory approval for a phase 3 trial.