Epidemiologist Benjamin Cowling has urged the government to set out what level of antibodies arrivals to Hong Kong will need to qualify for a reduced quarantine period, and whether those who've received mainland vaccine Sinovac will be able to pass the test put in place.
Chief Executive Carrie Lam on Monday announced that arrivals from overseas who are vaccinated will be required to undergo seven days of quarantine, down from 14 days, if they also test positive for antibodies against Covid-19.
“That passenger has to book a longer period of quarantine, say 14 days. But if he or she is being advised on the second day or third day that your antibody test is positive, so you can leave the designated hotel a week earlier,” she explained.
Professor Cowling from the University of Hong Kong's School of Public Health said their ongoing study showed people who'd had the Sinovac vaccine had a much lower level of immunity.
"I would very much like to know which tests are going to be done on arrival. On each of the tests that we were doing on the samples in our study, they were all positive one month after the second dose, but I don't know how long they would stay positive for, and maybe two, three, four, five, six months later at some point maybe some of those people who received Sinovac would start to test negative for antibodies instead of positive," he said.
"I can't tell you now about the timeline, and how long antibodies would stay positive for, but it does look because the starting point is quite low, it does look like people might regress to having negative antibodies at some point," he added.
Earlier this month Cowling said people who test positive for Covid antibodies should be exempt from doing quarantine.
He pointed out that Covid patients are usually discharged from hospital when they have antibodies, so it doesn't make sense to quarantine people in the same situation.
"If they did have Covid and they were in a hospital, once they show up with antibodies they can be discharged and so it doesn't really make sense to me that when people come in from outside, or if they're close contacts, if they have antibodies then they're not allowed to be exempt from quarantine," he said.
Yesterday, there were three imported coronavirus cases. Hong Kong has had no local cases for the past two weeks.