Health ministry likely to include rapid antibody testing for everyone at risk

Based on data and analyses prevented by its high-level technical experts committee on coronavirus disease (Covid-19), the health ministry is likely to extend testing

Based on data and analyses prevented by its high-level technical experts committee on coronavirus disease (Covid-19), the health ministry is likely to extend testing protocols to include rapid antibody testing for everyone at risk, including those outside hotspot areas.

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Once approved, these guidelines will replace the Indian Council of Medical Research’s interim advisory issued on April 2 that limited rapid antibody testing to hotspot areas.

Unlike the RT-PCR test that detects the virus’ genetic material (RNA) in throat swabs to diagnose current infection, rapid antibody test indicate if a person has been infected and has immunity.

The simple blood test, which takes 15-20 minutes to give results, will help identify people who were infected but never diagnosed, which will help map undetected infection and give the correct extend of the epidemic.

China and Singapore have used antibody tests to scale up testing and track infection, while Germany, Italy, Britain and the US, which approve the country’s first antibody test on Friday, plan to use it to get those who are immune back to work, keep those infected quarantined, and those with no immunity locked down.

“Rapid antibody testing will help us measure how widespread the infection is in the community, how long immunity works, and get the recovered back to work, which will help meet critical staff shortfalls in hospitals and end lockdowns in a phased manner to restore a semblance of normal,” said a clinician, who did not want to be named. “With infections in medical workers rising in India, it will help keep our health system intact,” he said.

The Maharashtra state government and the Brihanmumbai Municipal Corporation have already announced on Friday that all its health-workers will be tested using the rapid antibody test to detect if they have been infected and developed immunity to the virus..

“Who is to be tested and the scale of testing is notified by the Health Ministry, and updated from time to time. These are to be followed,” said Dr K. Vijay Raghavan, principal scientific advisor, government of India.

Antibody tests have the potential to take testing to scale, and companies are racing to meet the anticipated increase in demand. On Friday, Bangalore-based Bione launched a Covid19 home-screening test kit on Friday, and the US approved Cellex for a lab-based antibody testing. Pathologists expect the market in India to be flooded over the next few weeks following approval, which is expected next week.

“Finger-prick tests are fairly simple to do but chances of false negatives are high if the test is done in the first of week of infection. Antibody tests should look for immunoglobulin M (IgM) in the second week, and for immunoglobulin G (IgG) after the third week, to deliver accurate results. It still will not indicate how strong the immune response is, and for how long it will last,” said Dr Naveen Dang, founder chairman of Dr Dang’s Labs, which is one of the ICMR-approved private labs testing for Covid-19 in India.

The body responds to infection by generating two types of antibodies. IgM is generated first, at about seven days post-infection, and its levels then rises and fall by three to four weeks post-infection. The second type of antibody IgG, appears at about 10 days and can take up to three weeks to reach measurable levels. Since antibody responses vary widely with people, experts suggest that 21 days post-infection is about when most people are expected to show both IgG and IgM.

“Together, these antibodies, IgG and IgM, are expected to give protective immunity for a limited time; we do not yet know if and for how long these antibodies will protect, but that data will speedily come in,” said Dr Raghavan.

“A negative antibody test does not tell if the virus is present and if the body has not yet responded, but a positive does tell that the body was exposed to the virus. The antibody tests, even when used for screening, must be used with care, as with all tests, and interpreted by a professional. As of now, when so used, they can inform how groups of people have been exposed. When combined with nucleic acid tests, the antibody tests can give a complete status,” said Dr Raghavan.

“There are some very exciting developments with rapid virus (antibody) tests coming on to the market. There are being examined to ensure that they have the right sensitivity, which means they pick up small virus loads as well as big one, and they have specificity, which means they are not picking up other coronaviruses beside Covid-19. As soon as we know they are okay, they are going to be very important,” said Dr David Nabarro, the World Health Organization coronavirus special envoy.

RT-PCR remains the test of choice because of its accuracy and specificity at early stages infection, which is essential for containment as most people are most infective within to three days before show symptoms.

“In epidemics, such as Covid-19, testing for the presence of the viral genome in swabs is the first choice and this is done by what are generically called nucleic acid tests. These use a method called RT-PCR to detect the viral RNA. RT-PCT tests detect the viral RNA one to two days before symptoms appear and detection remains up to 12 days after symptoms,” said Dr Raghavan.

It is unlikely that patients who have antibodies will get reinfected so soon after recovery, say experts.”Obviously, antibody-positive persons can be declared as immune to Covid-19 and get free from social isolation. They won’t get infected or infect others,” said a public health specialist, requesting anonymity.