On April 4, the Indian Council of Medical Research issued an advisory to begin antibody blood tests for Covid19 in ‘hotspot’ areas that have reported clusters of migrants and for evacuee centers.
“[Serological testing] will help us know the exact proportion of population which was actually infected with the disease,” said Dr T Jacob John, former head of the Indian Council for Medical Research (ICMR)’s Centre for Advanced Research in Virology to Livemint.
Serological tests, also known as antibody tests, can determine whether a particular pathogen has been present by screening for the presence of antibodies. Antibodies are proteins used by the immune system to fight bacteria and viruses; if they are present in the bloodstream, they serve as evidence that the person’s immune system fought a particular pathogen.
Antibody tests can only be conducted on blood, but many such tests can be run with only a fingerpick test and a few drops of blood. Furthermore, these tests are cheaper, and faster to run, than the nasal swab tests for active coronavirus infection. However, antibody tests cannot confirm whether an infection is active and contagious, or whether the person’s immune system has effectively fought off the virus and they are no longer transmitting it.
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Antibody tests are vital to fighting the spread of Covid19 for several reasons. They may show that the person has been exposed to the virus and therefore, has some immunity to it, writes Delhi-based cardiologist, Deepak Natarajan, for The Wire. This would allow people who have been exposed to the virus, but were asymptomatic, to go back to work or school with a relative degree of safety for themselves and those around them.
Reliable antibody tests would also allow frontline healthcare workers who have been exposed and recovered to return to work without concern for themselves, their patients, or their families.
What we do no not yet know, Dr. Natarajan says, is how long the presence of these antibodies will confer immunity on people who have been exposed. Some recent experiments, give scientists reason to believe people could be immune to the novel coronavirus, at least for some time. But this evidence is complicated by other reports that 5%-10% of recovered patients in Wuhan did test positive again. Only time and data will help researchers understand better how — and for how long — coronavirus antibodies confer immunity after exposure.
Furthermore, the current antibody tests we have for Covid19 are not entirely reliable. We will need to aggregate far more data on how people’s immune systems respond to this novel virus before we can be entirely sure what determinations to make from the presence of the antibodies: which level confers immunity, and for how long.
The availability of a reliable and widely used antibody test will be essential in deciding when it will be safe to lift countries’ lockdowns and resume a normal life… at least until we have a widely available, effective vaccine.
