Serological-survey, antibodies and Elisa tests: What they mean in Covid-19 diagnosis

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Updated: Jul 27, 2020 8:04 AM

Coronavirus test: A serological survey is an antibody test conducted on a sample of the population to assess how many people have been affected.

The body’s usual response is to create antibodies to fight the infection. The body’s usual response is to create antibodies to fight the infection.

Covid-9 testing: The government last week released the results of the serological survey conducted in Delhi. Over 20,000 samples were tested between June 27 and July 10. This was the second serological survey conducted in the city. While the results of the first survey, which was conducted in two parts, have not been released yet. The results of the Delhi sero-survey show that Delhi had a positivity rate of 23.68% when adjusted for specificity and sensitivity, the adjusted prevalence was 22.86%.

What is a serological survey?
A serological survey is an antibody test conducted on a sample of the population to assess how many people have been affected. As it is difficult to determine the infection rates of a population based on RT-PCR and Rapid antigen tests, serological surveys are the best bet for the government to ready a response.

What is an ELISA antibody test?
The ELISA testing kit was developed by National Institute of Virology, Pune along with Zydus Cadila. The kit tests for IgG and IgM antibodies in the population. It’s reliability is tested using two indicators: specificity and sensitivity. The test, according to literature, has a 97.7% specificity and 92.1% sensitivity.

What are IgG and IgM anitbodies?
The body’s usual response is to create antibodies to fight the infection. So, the body produces Immunoglobulin M (IgM) and Immunoglobulin G (IgG) antibodies to fight against a pathogen. The IgM is the first response created once the body is infected and can be detected within 4-7 days after the infection starts. These are short-lived. The IgG bodies, however, have a longer life span and are detectable at a later stage say 14 days after the infection. But in the case of coronavirus, it is known, how long these can survive in the body. Some reports suggest that in a few cases IgG antibodies have not survived beyond a few months. If that is indeed the case, then vaccine development becomes more challenging. However, preliminary studies from Oxford and others have shown promise.

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