While the low sensitivity of rapid antigen tests arises from not isolating the viral RNA from the swab samples and amplification of the DNA before detection, the two indigenously developed tests follow these two vital steps, the reason why the sensitivity and specificity are far superior than that of the rapid antigen tests.

Thanks to the pandemic, scientific institutions in India have been able to demonstrate their ability to rise to the occasion when the situation demands and also emphatically show why India should increase funding for science research and development.

The recent approval by ICMR of two indigenously developed tests that are rapid, low-cost and have high sensitivity and specificity provides the much-needed boost to scale up daily testing manifold without compromising on accuracy. After carrying out about one million tests each day for the last few weeks, India for the first time tested nearly 1.5 million samples on October 21.

While the majority of the tests done each day so far were the rapid antigen tests, which have low sensitivity, the tests developed by the Delhi-based Institute of Genomics and Integrative Biology, a CSIR institute, and IIT Kharagpur will now enable India to shift to more accurate tests. The low sensitivity of rapid antigen tests meant that even people with symptoms were handed out a negative result nearly half the time, leading to many cases going undetected.

With unrestricted movement of people, opening up of most business establishments, beginning of the festival season and winter around the corner, the requirement for a rapid, low-cost test with high accuracy has become particularly important to check the virus spread through early detection and repeated testing of even asymptomatic cases. The availability of locally developed tests with higher accuracy will now enable States to offer tests on demand as required by the ICMR in its September 4 advisory while keeping the costs of tests low.  

Why rapid antigen tests have low sensitivity

While the low sensitivity of rapid antigen tests arises from not isolating the viral RNA from the swab samples and amplification of the DNA before detection, the two indigenously developed tests follow these two vital steps, the reason why the sensitivity and specificity are far superior than that of the rapid antigen tests. But at the same time, both the tests developed locally do require minimum laboratory infrastructure to isolate the viral RNA from the samples.

Rural areas and rapid antigen tests

For that reason, India has to still rely on rapid antigen tests in rural areas that have no laboratory infrastructure of any kind. But the tests developed by the Indian institutions, once commercially available, can readily replace the rapid antigen tests in places where such laboratory infrastructure is in place.

Rapid antigen tests will become less important even in rural areas once research institutions in India succeed in developing protocols and tests for using saliva rather than swabs, and do not require isolation of viral RNA from patient samples before amplification and detection. Field testing and validation of such protocols is now pending.

Relying on saliva samples instead of swabs would mean non-invasive means of collecting patient samples, and probably even self-collection. This would make testing even more accessible by not relying on trained personnel to collect swabs and also reduce the risk of health-care workers getting infected during the swab collection procedure. 

Published in The Hindu on October 23, 2020