Delhi’s serological survey
The Ministry of Health and Family Welfare declared the results of a serological survey carried out in Delhi between June 27 and July 10, which showed that 22.86% of the people surveyed had developed Immunoglobulin G (IgG) antibodies, indicating they had been exposed to the novel coronavirus that causes Covid-19.
What is a serological survey?
• A serological survey seeks to assess the prevalence of disease in a population by detecting the presence of specific antibodies against the virus.
• A serological test is performed to diagnose infections and autoimmune illnesses. It can also be conducted to check if a person has developed immunity to certain diseases.
• The survey included the IgG Enzyme-Linked Immunosorbent Assay (ELISA) test which estimates the proportion of the population exposed to SARS-CoV-2 infection.
• The IgG test is not useful for detecting acute infections, but it indicates episodes of infections that may have occurred in the past. The test has been approved by ICMR for its high sensitivity and specificity.
The seroprevalence study found the presence of antibodies in 22.86 per cent of the people surveyed.
This rate of seropositivity cannot, however, be extrapolated over Delhi’s entire population. Since it is not possible to test everyone in the population, serological studies are used as a tool to make an estimate of the extent of disease spread in the community.
In April, the Indian Council of Medical Research (ICMR) had conducted a pilot serosurvey in 83 districts in 21 states.
The initial results, which are being peer-reviewed, indicate that the percentage of the general population that could have been infected in the past was 0.73 per cent, with urban areas showing a higher prevalence of 1.09 per cent.
ICMR has said it would soon launch a follow-up serosurvey across the country.
The government has said that results show that a significant proportion of the population is still vulnerable to contracting the novel coronavirus infection.
Containment measures need to continue with the same rigour. Non-pharmacological interventions such as physical distancing, use of face mask/cover, hand hygiene, cough etiquette and avoidance of crowded places etc. must be followed strictly.