Health authorities have been urged to allow antibody serology test results to be used as proof of Covid-19 infection to help residents stuck in vaccine pass limbo and better gauge the number of positive cases in Hong Kong. Residents unable to register their previous infections on the rapid antigen test (RAT) reporting system had expressed concern about getting vaccinated too soon after recovery, prompting calls from medical experts and a community leader for the government to help those caught in a bind. Officials also admitted there were many unreported cases and that further analysis was warranted to ascertain the actual number of Covid-19 infections and the death rate in the city. Hong Kong Covid death rate ‘could be lower than thought’, city leader says Under the vaccine pass scheme, those entering 23 types of premises, including restaurants and supermarkets, must have had at least one dose of a Covid-19 vaccine. By April 30, they need to have two doses, and by May 31, three. Recovered Covid-19 patients are exempted from vaccination for up to six months. While children aged below 12 are not affected by the policy, schools will only be allowed to conduct full-day in-person classes if 90 per cent of their students have taken two doses of vaccines. Residents who have registered their infection records can present paper documents to prove vaccine exemption when entering premises under the scheme. Paul Zimmerman, Southern district councillor, said the government should allow people who did not manage to register their previous infections to upload their antibody serology test results. The current self-reporting system, launched on March 7, accepts only test results conducted within 48 hours starting from March 6. Those infected between February 26 and March 5 were given a one-week registration window, which closed on March 14. “We are talking about people with kids who are worried about having their child get the vaccine too early after recovering from Covid-19,” Zimmerman said. Respiratory expert Dr Leung Chi-chiu supported the idea, saying antibody serology tests were an effective way to prove a prior infection, although there were limitations in the accuracy of most of the serology tests currently provided by private medical centres. As these serology tests measure the level of two types of protein antibodies, Leung said it would be harder to prove a prior infection if a patient was previously injected with an inactivated vaccine like Sinovac, since they would have one of the protein antibodies through the jab. Antibody levels varied among individuals and these two types of protein antibodies would drop substantially six months after infection or vaccination, he added. “It will then depend on when they took the vaccine and whether an increase or decrease of antibodies could be detected,” Leung said. Separately, Professor David Hui Shu-cheong, a respiratory diseases expert from Chinese University, said conducting large-scale serology testing in the community would be a more accurate way of estimating the number of people who had been previously infected with Covid-19, a figure that would be helpful in determining the fatality rate in Hong Kong. Hui said laboratories at medical schools could carry out more accurate serology tests that measured a third type of antibody, which would develop after infection and would not decline significantly in volume six months after recovery. “The reference value of [such serology a study] will be higher,” Hui said. “After drawing blood from tens of thousands of people, we will then know how many people have actually been infected.” “This kind of study has to be done at the end [of the outbreak] when you have enough random samples across age groups for it to be meaningful,” he added. Hong Kong’s vaccine pass hits unvaccinated hard, but some still refuse jabs Hong Kong’s tally of confirmed cases currently stands at 1,143,788, while the total number of related deaths has reached 7,571. But various experts have put the actual number of Covid-19 infections in the city at anywhere from 2.5 million to 5 million. Leung said Covid-19 patients could get their next dose safely three months after recovering, as the immune response from the vaccine would be weakened if the shot was taken within three months of recovery when antibody levels were still high. In response to a query from the Post , the Food and Health Bureau said the government was making relevant system enhancements to allow residents to add their recovery records to the “Leave Home Safe” risk-exposure app. The enhancements are expected to be completed in May. But it did not say whether the move would allow people to report previous infections, and did not advise on what recovered patients who previously failed to register could do at present. The Centre for Health Protection suggested last Friday that unreported cases could email authorities for follow-up action. Andy, a management consultant in his 40s, and his wife were among those who missed the registration window as they were infected two weeks before the launch of the RAT reporting system. Andy said he hoped the government would allow cases like them to register, as he was worried about arrangements for his unvaccinated six- and four-year-old children to go back to school. He said his wife had tried to secure exemption certificates from 10 different private doctors in Kennedy Town but to no avail. “The doctors were helpful, but they didn’t know what to do [with our cases]. Exemption letters were not offered to us, perhaps because we aren’t their patients,” Andy said. Additional reporting by Elizabeth Cheung