New ICMR plan for states to expand antibody tests
For several viral infections, antibody tests are useful for disease detection after 5–7 days of illness. Understanding related to antibody tests for Covid-19 is evolving and several tests are being developed globally.
After completing a pilot sero-survey (a test of the blood serum of a group of individuals) last week to check the level of exposure to the Sars-CoV-2 virus that causes Covid-19 in the community using Elisa-based antibody testing, the Indian Council of Medical Research’s (ICMR) on Saturday sent an advisory to all states to expand the survey.
ICMR has prepared a comprehensive list of categories of people who should be tested as part of the sero survey, including high-risk or vulnerable populations (health-care workers, frontline workers, immune-compromised individuals, individuals in containment zones, security staff, prisoners) to know who has been infected in the past and has now recovered.
“ICMR conducted the pilot survey to get a basic sense of how India is in terms of disease spread currently, for which the results should be out in some time. However, periodic sero-surveys are necessary to establish a trend and the states have been asked to take it forward and keep doing it periodically to know the prevalence of the disease at ground level,” said a senior ICMR official, who did not wish to be identified.
The blood samples will be tested for detecting IgG antibodies using the Elisa method ((IgG is an antibody that develops later as compared to the other antibodies, hence, determines a past infection). The Elisa method is an enzyme-based laboratory test that detects and quantifies antibodies in blood that will determine a past infection due to the virus.
For several viral infections, antibody tests are useful for disease detection after 5–7 days of illness. Understanding related to antibody tests for Covid-19 is evolving and several tests are being developed globally. The IgG antibodies generally start appearing after two weeks of the onset of infection, once the individual has recovered after infection and last for several months. The IgG test is not useful for detecting acute infection but indicates episodes of Sars-CoV-2 infection in the past, say experts.
“Sero-surveys help to understand the proportion of population exposed to Sars-CoV-2 infection including asymptomatic individuals. Depending upon the level of sero-prevalence of 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,” said ICMR in a statement.
Scientists at ICMR-National Institute of Virology, Pune have developed and validated an indigenous IgG Elisa test for antibody detection for Sars-CoV-2.
The 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 pharma companies such as Zydus Cadila, J Mitra & Company, Meril Diagnostics, Voxtur Bio, Trivitron Healthcare, Karwah Enterprises and Avecon Healthcare.
“The technology has been transferred to various entities without exclusivity clause and therefore can be further shared with others as per demand and capability. ICMR has offered to provide technical support to States/ UTs, if required, in planning and carrying out sero-surveys using IgG Elisa test kits and also interpreting the results,” said the research body.
Experts on infectious diseases, however, feel that merely knowing whether the population has developed antibodies against the virus is not enough.
“Merely knowing the volume of people who have been infected will only provide the sense of the spread of the disease; what we must try to know is the quantity and quality of antibodies being produced against the virus. Also, for how long these antibodies stay in human blood so as to know if it’s enough to offer protection against the disease,” says Dr Lalit Kant, former head of the epidemiology division at ICMR