Unlike the currently used molecular test that uses oral swab samples, the antibody test developed by Duke-NUS Medical School has several advantages — it can detect past infection in people who have now recovered, it relies on blood samples, and can identify asymptomatic cases.

Using an antibody test developed by the Duke-NUS Medical School that relies on blood samples, the Singapore Ministry of Health has been successful in identifying two people who were infected with the novel coronavirus (SARS-CoV-2) and have since recovered. The antibody test can be used for detecting people infected with novel coronavirus but are asymptomatic or exhibit only mild symptoms. The Singapore Ministry of Health announced this during a press conference held yesterday.

Advantages of antibody test

In an email, Dr. Danielle Anderson from the Emerging Infectious Diseases Programme, Duke-NUS Medical School said the “sensitivity and specificity [of the test] should be 100% since we have two parallel tests to ensure that we do not capture false negatives/positives.”

Unlike the currently used molecular test that detects the presence of viral genetic material in oral swab samples, the diagnostic test developed by Duke-NUS Medical School detects antibodies in blood samples developed by the immune system when infected with the novel coronavirus.

“Antibodies will start appearing in the body starting a few days after infection and will peak in about two-three weeks after infection. [So] the test may not be able to detect antibodies if the person is tested too soon after infection,” Dr. Anderson explained.

While the currently used molecular test has low sensitivity and cannot identify people who have recovered from COVID-19 illness as they will no longer harbour the virus, antibodies produced by the immune system in response to infection will be present in the blood for a long time. This makes the antibody test particularly important to trace even people who have recovered from illness.

How the test works

“We developed assays which are not new assays but using them in this context we could look for antibodies in patients. We could trace back patients who have been infected previously,” Dr. Danielle Anderson, Scientific Director of the Duke-NUS ABSL3 facility said during the press conference.

Explaining how the antibody test is carried out, Dr. Anderson said in the email: “The live coronavirus is tested against the antibodies present in the patients’ samples. If there are antibodies against the coronavirus, the antibodies will prevent the coronavirus from replicating. This is a definitive readout of the patient being previously infected by the virus because you will not have antibodies against the virus if you have never been infected by it before.”

On January 30, the Duke-NUS Medical School announced that in collaboration with other institutions/hospital it had successfully cultured the novel coronavirus from an infected person, thus becoming the third country outside China to do so.

According to the Ministry of Health release, the researchers had used the virus and genetic material derived from the virus to “develop several specific laboratory tests to detect the virus-specific antibodies for contact tracing and other applications”.

Antibody test confirms past infection

The antibody test was put to use to confirm past infection (late January) with novel coronavirus in two people who have since recovered. Two different antibody testing platforms (virus neutralisation assay and ELISA assay) were used to confirm past infection. This became possible as these people, despite having recovered from COVID-19 illness, still had “very high levels of the virus-specific antibodies in their blood”.

The positive test result in the two people helped the Health Ministry to establish the links between two church clusters and the source of infection.

Published in The Hindu on February 26, 2020