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Should you get a covid-19 antibody test?

Private laboratories across India are offering antibody testing to individuals but a ‘positive’ result doesn’t mean you can’t get infected with covid-19

A medic takes blood samples for serological survey to analyse the spread of COVID-19, at Paharganj in New Delhi
A medic takes blood samples for serological survey to analyse the spread of COVID-19, at Paharganj in New Delhi (PTI)

On 23 June, the Indian Council of Medical Research (ICMR) allowed private laboratories across India to conduct antibody tests. The idea of the tests, it said, was medical surveillance, not diagnosis. “It is advised to share the comprehensive report of antibody testing with ICMR," it added.

Since the notification, private laboratories have been offering the tests for prices ranging from 500-1,250. According to news reports, labs like Thyrocare and Suburban Diagnostics in Mumbai tested 12,500 and 10,100 people in Mumbai and found antibodies in 27.3% and 24% cases, respectively. A spokesperson for Metropolis Labs India, which also offers the tests in metros, said customers include “some corporates, especially those from essential services".

Antibodies are proteins generated within the body to fight off a disease. So you develop antibodies for a disease after you have been have been infected and pulled through it. The test results in the Mumbai examples, for instance, indicate that one in every four people tested had been exposed to covid-19 and had developed antibodies against it.

So does this mean they are safe from the virus? The short answer is, no. And that is largely due to the limitations of the antibody tests on offer.

“When you test positive for antibodies, all that tells you is that you have been exposed to the virus in the past few weeks or months," says Satyajit Rath, an immunologist from the Indian Institute of Science Education and Research (IISER), Pune. “What it does not tell you is whether the immune response you have had is necessarily a protective immune response against future infections. It also does not tell you how long such a hypothetical protection might last."

There’s one more limitation to the test. According to the Centers for Disease Control (CDC), the national public health institute in the US, “An antibody test may not show if you have a current COVID-19 infection because it can take 1-3 weeks after infection for your body to make antibodies."

The World Health Organization (WHO), too, has pointed out that covid-9 antibodies last for around three months in body. This points to the possibility of a chance of re-infection among survivors.

Even if one goes ahead and takes the antibodies test, there is a possibility that the results might give a false positive or a false negative, adds Dr Rath. “There is a small chance that antibodies’ low-level positivity is detected even among some people who have not really been exposed to the virus earlier. On the other hand, we also have some evidence that a small percentage of people—10%, according to some studies—exposed to the virus do not develop antibodies."

With all these caveats, is the antibody test of any use? It may not be so for an individual but it does help guide community health response. “An antibody test is helpful in serological surveys and can help understand the level of infection in different parts of cities and towns," says the spokesperson from Metropolis Labs. “It can also help identify people who have recovered from COVID-19 and these people may be eligible to donate plasma. This plasma could be used to treat others with severe disease and several civic bodies across the country have begun plasma therapy."

Further, it helps authorities determine public health policy and strategy. In July, antibody tests conducted as part of a sero-survey in three regions in Mumbai—Matunga, Chembur and Dahisar—found antibodies in 40.5% of those tested. Similar tests in Delhi found antibodies among 29.1% of those surveyed.

These surveys helped establish that the virus spread was far more widespread than the daily numbers released by the ICMR indicate. A large number of virus carriers never developed symptoms, which helped the surveyors understand the extent of asymptomatic infections.

“If you feel safer taking the tests, and if you have the money to afford it, go ahead and do that," says Dr Rath. “But do not treat a positive test as though it is an immunity passport, because it is not. Please stay on guard."

So maintain physical distancing, wear masks, use sanitizers and wash hands regularly. “It’s the basics," adds Dr Rath, “but they work."

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