News: sero-surveillance study conducted by National Center for Disease Control [NCDC], MoHFW, in Delhi.
- Survey teams were formed for all 11 districts of Delhi and samples were collected from selected individuals after taking written informed consent.
- Their sera were tested for IgG antibodies and infection using COVID KAVACH ELISA approved by Indian Council for Medical Research [ICMR].
- It is one of the largest sero-prevalence studies conducted in the country using the ELISA testing.
- These tests performed are not a diagnostic test but only provides information about past infection due to SARSCoV-2 in individuals.
- Repeated sero-surveillance or antibody testing done over time generates important evidence for assessing the spread of the pandemic from time to time.
- Study suggests prevalence of IgG antibodies across Delhi is 23.48%.
- Study results suggests large number of infected persons remain asymptomatic.
- Prevalence believed to be contained due to proactive measures taken by Delhi government. However, a significant proportion of population is vulnerable.
- More efforts are required such as physical distancing, use of face mask/cover, hand hygiene, cough etiquette and avoidance of crowded places etc.
About ELISA (enzyme-linked immuno-sorbent assay) testing
B cells of the immune system produces Y-shaped protein i.e. antibodies in response to exposure to antigens. Antibodies binds to the antigens entered into the body and tags them for attack from immune system.
Formation of antibody is not a very rapid process. IgM are 1st antibodies developed in the body i.e. within 7 to 10 days after exposure. It is only after about 10 to 14 days, the body begins making IgG antibodies, that is much stronger compared to IgM antibodies.
The Enzyme-Linked Immunosorbent Assay (ELISA) is a technique used to detect antibodies in a person for the exposure to infectious diseases.
Term enzyme-linked suggests it uses enzymes to detect presence of antibodies in a blood sample
ELISA test is of two types depending on the antibodies: (1) immunoglobulin M (IgM), (2) immunoglobulin G (IgG).
- Immunoglobulin M (IgM): detects antibodies produced in early stages of infection
- Immunoglobulin G (IgG): detects antibodies developed in later stage of infection
In May, ICMR Approved Covid Kavach ELISA IgG test developed through the National Institute of Virology in Pune.
ELISA test for Covid-19 is only approved for sero-surveys i.e. for estimating the proportion of population exposed to COVID-19. It is not a diagnostics test. It suggests the level of public health interventions required in an area.
RT-PCR (reverse-polymerase chain reaction) tests are used for diagnosis and treatment of Covid-19 in individuals. It is a confirmatory test for COVID-19.