Serological tests: One more tool in India’s fight against Covid-19

As new infections continue to rise, India has begun preparations to start serological testing in the country, which may offer clues on how widely the new coronavirus has spread into the population and if people have developed immunity.

The Indian Council for Medical Research (ICMR) has already invited tenders for procurement of antibody testing kits which have been approved by US-FDA, EUA CE or NIV Pune. A tentative requirement of 10 lakh kits has been placed, which was later decreased to 5 lakh kits due to availability issues amid high demand from international manufactures.

While India has so far reported 979 positive cases so far, virologists the actual number could be higher, and serological tests could give real attack rates of the virus.

“Vast majority of people will have no symptoms. Younger the age more is the likelihood of such asymptomatic cases. But we cannot know these numbers until we do good quality antibody testing. It will help us know the exact proportion of population which was actually infected with the disease,” says Dr T Jacob John, former head of the Indian Council for Medical Research (ICMR)’s Centre for Advanced Research in Virology.

This is unlike the current nucleic-acid (RT-PCR) test done by laboratories. While a real time-Polymerase Chain Reaction (PCR) test is used to confirm Covid-19 in patients who are currently ill, the serological tests go a step further.

They allow scientists to even test seemingly healthy people who may have been infected with COVID-19 in the past but recovered without showing any symptoms. This is done by measuring the amount of antibodies from their blood samples.

“People, who have been acutely infected and recovered, have antibodies against the virus. Antibodies mean there is immunity. So, one is protected and not afraid of getting the virus. But, we do not know how long this immunity lasts, may be two years to ten years,” said Gagandeep Kang, clinical scientist at Christian Medical College, Vellore.

Our body releases two types of antibodies - IgM which get released usually three days after one starts showing symptoms and indicates the body is responding to an infection. And, IgM- is released much later and shows if the person was infected in the past and has recovered.

The government could use these tests to carry out sero-epidemiological studies and screen how much population has been exposed to the virus already and have developed immunity.

“It will enhance our preparedness. Imagine if we have to get factories running again and need to get people back to work, then in that case if we have the potential to identify people who can safely go out again, that would be helpful. But we must understand, that we need both the tests,” said Dr Anurag Aggarwal, Director of the CSIR-Institute of Genomics and Integrative Biology (CSIR-IGIB), New Delhi.

This could even help define countries’ strategies in the worst-case scenario when healthcare workers start getting infected as cases surge. In that case, healthcare workers who have the antibodies and are not at risk can be put on the frontline - an approach being experimented by United Kingdom.

Some of the biggest serology is being done by China and South Korea. But, there are challenges regarding sensitivity, specificity and accuracy of these tests which limits their effectiveness for diagnosis.

But scientists also believe that it could help provide point-of care testing facilities, as the situation evolves and there is a surge in infected cases.

“If large-scale testing has to be done, serology may be the way. These are complementary tests which are less complex and helpful in urgent situations for they can be done locally,” said Dr Naveen Khanna, ICGEB International Centre for Genetic Engineering and Biotechnology (ICGEB).