The Indian Council of Medical Research (ICMR) and the Pune-based National Institute of Virology (NIV) early this week announced that they had developed and validated the indigenous IgG ELISA test called 'COVID KAVACH ELISA' for antibody detection for the novel coronavirus.
The government said the specificity of COVID KAVACH ELISA kit is 97 percent, while sensitivity is 92 percent. The ICMR will be soon deploying ELISA testing for conducting a national-level surveillance study on the prevalence of COVID-19.
The ICMR has partnered with Zydus Cadila for mass-scale production of the ELISA test kits. To be sure, there are many large multinationals such as Abbott which have received approval to import ELISA test kits.
Abbott's SARS-CoV-2 IgG test identifies the IgG antibody, which is a protein that the body produces in the late stages of infection and may remain up to months and possibly years after a person has recovered.
What is ELISA test?
Enzyme-Linked Immunosorbent Assay or ELISA is a serology test or blood-based test for SARS-CoV-2. The test is used to identify whether a person has been exposed to COVID-19 or not. This is done by detecting the presence of immunoglobulin (Ig)M and IgG antibodies. It is generally a lab-based test.
What is unique about the test?
The test relies on antibodies to detect a target viral protein or antigen using highly specific antibody-antigen interactions. The test involves coating viral proteins (like spike protein) on a plate. Patient samples are then applied on viral protein, and if the patient has antibodies to the viral protein they bind together. The bound antibody-antigen can then be detected with another wash of antibodies that produce a colour. Elisa is not only a test for positive or negative of the infection, but also gives us a measure of antibodies. This is particularly important for developing a vaccine and also for convalescent plasma therapy.
How is ELISA different from current tests?
The widely used RT-PCR tests to diagnose cases of COVID-19 only indicate the presence of the virus or not. It will not help us know if a person was infected and subsequently recovered. RT-PCR tests are slow and need some expertise in collection of nasal swab. In contrast, ELISA tests can give results in 2-5 hours and require only a simple finger prick.
The rapid antibody test works on the same principle as ELISA test, but they are less accurate. The controversy around the efficacy and the pricing of rapid antibody tests is also pushing the government to consider other testing methods.
How useful is ELISA test
ELISA helps us get a sense of the prevalence of the disease in a population by identifying individuals who have developed antibodies to the virus. This will help plan better in opening the economy. The ICMR is doing a national survey using ELISA test to find out the prevalence of COVID-19 in the community.
What is CLIA test?
Chemiluminescence Immunoassay or (CLIA) is also a serology test using a different method. The advantage of CLIA is it will help in the early detection of virus compared to ELISA, and is also suitable for conducting tests in large volumes. It can also detect low-intensity samples. However, CLIA analysers need large labs and are expensive.
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