Post-vaccination antibody tests unnecessary: experts

Medical experts have told RTHK that it is unnecessary for the general public who have been vaccinated against Covid-19 to measure their immunity level by purchasing antibody tests – calling them a waste of money and warning that the results could be misleading.

So-called vaccine efficacy tests can cost up to HK$800, and involve taking a blood test two weeks after vaccination to check antibody levels. The tests have been gaining in popularity at some private clinics and laboratories.

“Are you wondering whether the vaccine is effective?” one clinic asks on its website.

“Taking a Covid-19 antibodies test after getting vaccinated helps to evaluate the immune effect and ensure that the vaccine can effectively fight the virus,” it says.

A member of staff at one clinic that RTHK called said the test could even be used to show how long vaccine protection will last.

“You have to take this blood test and you’ll know how much protection the vaccine has given your body. The doctor will explain to you… if it’s high, it can last around one year. Everyone is different,” she said.

But infectious diseases expert Professor Ivan Hung from the University of Hong Kong dismissed such claims.

“That’s misleading. That’s not true at all… because each individual can sustain the antibody level at different rates. It’s very difficult to project just based on one single value of your antibody level,” he said.

“We would not recommend individuals to take the antibody tests and it’s not necessary.”

An expert advising the government on its coronavirus strategy, Professor David Hui from the Chinese University, questioned the accuracy of the tests offered by the private clinics and laboratories.

“The usual blood tests organised by the usual laboratories is only testing the B cell response. B cell response is only one of the weapons conferred by the vaccine. There is also T cell response, which is not reflected in the conventional blood tests,” he said.

“So even if the test on the B cell response is negative, it doesn’t mean the person is not having any effect, there may be T cell response. And T cell response can only be measured in university laboratories or high power laboratories.”