To gauge the spread of Covid-19, the state government plans to start rapid antibody tests from August. The state health officials will zero in on the kit by the end of the next week, while a four-member committee has been formed to analyse the accuracy of the available antibody testing kits.

In Maharashtra, more than 3 lakh people have been infected with Covid-19 since its outbreak in March. Medical experts believe that as 80% of the patients are asymptomatic, a large number of the silent carriers are not accounted for. To identify such people, the Indian Council Medical Research (ICMR) has given the state government permission to start rapid antibody testing.

Antigens are molecules that stimulate an immune response. Antibodies (immunoglobulins) are Y-shaped proteins produced by the immune system in response to exposure to antigens. An antigen test reveals if a person is currently infected with a pathogen, while the antibody test tells if he was infected over the month.

“Just like the national sero survey, the kits will be used for identification of people carrying the antibodies for Sars-Cov-2 that causes the infection. Unlike the rapid antigen kits, the antibody kits will not be used for diagnosis of patients,” said Dr Sudhakar Shinde, chief executive officer of Mahatma Jyotiba Phule Jan Arogya Yojana.

In the first week, Immunoglobulin M (IgM) antibodies are produced and gradually, the body starts developing IgG antibodies that stay in the blood for almost a month. “Depending on the types of antibodies and their concentration, we can estimate if the person is in the early stage of infection or the stage of recovery,” said Dr Lancelot Pinto, an epidemiologist from Hinduja Hospital.

By the end of next week, the state will decide which testing kit is to be used. A four-member committee headed by Dr Shinde will test all available antibody test kits and send their findings to the Indian Council of Medical Research (ICMR) for approval. “There are so many testing kits which have been recently developed by different companies and scientists. We will run tests on all those kits to find its accuracy. There are several determinants and parameters,” he said.

Dr Ranjit Mankeshwar, JJ Hospital’s dean, who is also part of the committee, said the kit will mostly be used among frontline warriors. “As it is not a diagnostic tool, it will mostly be used among doctors, volunteers who are involved in screening, treatment and contact tracing. We are yet to decide if the kit will be used for mass screening in containment zones,” he said.

In April, the central government had procured 5.5 lakh rapid antibody testing kits from China. The Maharashtra government procured 75,000 for testing. But before the process could begin, the Central government withdrew the kits after some of them were found faulty.

According to experts, although antibody testings don’t give 100% accurate results, it can be useful to understand the pattern of the spread of the virus and surveillance among the population. “Antibody testing gives false reports too, but it can help in analysis of a larger community. It is not a perfect science, but can be helpful in a population with a large number of asymptomatic patients,” said Dr Om Srivastava, city epidemiologist and a part of the state task force for Covid-19.

Antigen and antibody test

Antigens are molecules that stimulate an immune response. Antibodies (immunoglobulins ) are Y-shaped proteins produced by the immune system in response to exposure to antigens. The first antibody produced is Immunoglobulin M (IgM). After seven-14 days of the exposure, the second antibody, Immunoglobulin G (IgG) is produced, which stays in the body for a long period.

An antibody test reveals if a person was exposed to an infection, by detecting the type of antibodies in the blood. If the test is done too early, before the antibodies are produced, the result may be negative. An antigen test reveals if a person is currently infected with a pathogen.

Once the infection is cured, the antigen disappears, but antibodies remain in the body for a month. “As it is not a diagnostic tool, it will mostly be used among doctors, volunteers who are involved in screening, treatment and contact-tracing,” said Dr Ranjit Mankeshwar, JJ Hospital’s dean.