Usefulness of testing population for antibodies unclear

Some are asking whether Singapore should do population testing for antibodies - which people who have recovered from the infection would have in their blood. PHOTO: ST FILE

Singapore has been actively testing people with respiratory symptoms and close contacts of Covid-19 patients for the coronavirus.

But with growing evidence that there are people who are infected but appear to be only mildly sick or not at all, questions are being raised about whether there are many who have been infected, yet do not know it.

Some are asking whether Singapore should do population testing for antibodies - which people who have recovered from the infection would have in their blood.

But the experts do not think so.

Professor Leo Yee Sin, executive director of the National Centre for Infectious Diseases, said that at the moment, "we do not know how to use this tool effectively to give us a better understanding".

How such tests can be used "to estimate the level of the protection in an individual as well as in the community is still an area that is under intense study, discussion and debate at this point in time", she said.

Professor Teo Yik Ying, dean of the National University of Singapore's Saw Swee Hock School of Public Health, added that serology, or testing for antibodies, is to find out the proportion of a population that is immune to the virus.

However, he said other countries as well as the World Health Organisation are now grappling with the question of the extent of immunity such antibodies confer on people.

He said it is a "huge assumption" to think that "if I have the antibodies in my blood, I am immune to subsequent infection", because some doctors are suggesting patients can be reinfected.

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While agreeing that there is still a lot not known about the virus, Prof Leo said cases of reinfection may actually be because the patient has recovered but still carries the virus.

She said this does not mean the person is still infected. "It just means the body is taking time clearing the virus from the respiratory system."

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A version of this article appeared in the print edition of The Straits Times on April 23, 2020, with the headline Usefulness of testing population for antibodies unclear. Subscribe