The Indian Council of Medical Research (ICMR), country's apex health research body has advised states to conduct sero-survey to measure COVID-19 exposure in the population using IgG ELISA test.
The test kit that will be used in the survey was developed and validated indigenously by scientists at ICMR-National Institute of Virology (NIV) for antibody detection for SARS-CoV-2.
What is the purpose of sero-survey?
Seroprevalance, or sero-surveys, would help understand the proportion of population exposed to SAR-CoV-2 infection including asymptomatic or individuals who do not show any signs of COVID-19.
Depending on the level of sero-prevalence of the infection, appropriate public health interventions can be planned and implemented for prevention and control of the disease.
Periodic sero-surveys are useful to guide the policy makers. For instance, a survey in high risk or vulnerable populations such as healthcare worker, frontline workers, immune-compromised individuals, individuals in containment zones, etc. would show who has been infected in the past and if they have now recovered.
Once bitten, twice shy
The government had earlier attempted to do a nationwide sero-survey. But the plan was shelved after it found that the imported Chinese rapid antibody test kits had accuracy issues.
This time, ICMR seems to have ironed out the issues. The agency has said that test has undergone intense validation in three stages and has been found to have high sensitivity and specificity. To fast track production and increase availability of the IgG ELISA test, ICMR has transferred this technology to many pharmaceutical companies such as Zydus Cadila, J Mitra & Company, Meril Diagnostics, Voxture Bio, Trivitron Healthcare, Karwah Enterprises, Avecon Healthcare, etc. The technology has been transferred to various entities without an exclusivity clause.
Also read: Is herd immunity our best bet in the fight against coronavirus?
How accurate are these tests?
ICMR had earlier claimed that these test kit has an impressive 100 percent specificity and 98 percent sensitivity.
Sensitivity is the percentage of persons with the disease, who are correctly identified by the test, and specificity refers to the percentage of people without the disease who are correctly tested negative or excluded by the test.
High accuracy is extremely crucial if we have to correctly estimate the prevalence of COVID-19 infection in the population. Also, care has to taken while conducting the survey to avoid sampling bias.
How is IgG antibody test useful in sero-survey?
Currently, real-time RT-PCR test is considered gold standard frontline test for diagnosing of SARS-COV-2, which causes COVID-19. The test is useful only when performed in the acute stage of infection that is less than seven days.
For several viral infections, antibody tests are useful for disease detection after five-seven days of illness. IgG antibodies generally start appearing after two weeks of onset of infection once the individual has recovered after infection and last for several months. Therefore, the IgG test is not useful for testing acute infection but indicates episode of SARS-CoV-2 infection in the past.
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