Delhi’s Serological Survey

Recently, the Ministry of Health and Family Welfare declared the results of a serological survey carried out in Delhi between 27^th June and 10^th July, 2020.
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 blood samples were collected from selected individuals after taking their written, informed consent, and their sera were then tested for IgG antibodies and infection using the ICMR-approved COVID KAVACH ELISA kit.

Key Findings of the Survey

Results of the sero-prevalence study show that on an average, across Delhi, the prevalence of IgG antibodies is 23.48 %.
The study also indicates that a large number of infected persons remain asymptomatic.
Nearly six months into the epidemic, only 23.48% of the people are affected in Delhi,which has several pockets of dense population.
This can be attributed to the proactive efforts taken by the Government toprevent the spread of infection including prompt lockdown,effective containment and surveillance measures, including contact tracing and tracking, as well as citizen’s compliance had yielded benefits.

Looming Concerns

The government has said that results show that a significant proportion of the population is still vulnerable to contracting the novel coronavirus infection.
The 48% rate of sero-positivity cannot, however, be extrapolated over Delhi’s entire population.

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 test indicates past infections (and which triggered an immune response), and is not used to detect active infections.

Benefit

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.

Recent Sero-Survey

In April, 2020,the Indian Council of Medical Research (ICMR) had conducted a pilot sero-survey 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.

Since large proportion of the population is susceptible and infection can spread, non-pharmacological interventions such as physical distancing, use of face mask/cover, hand hygiene, cough etiquette must be followed strictly.
Containment measures need to continue with the same rigour.
Local lockdown measures need to continue as advised by the Central Government, especially in containment areas.
High risk groups, that includes elderly population, people with chronic morbidities, pregnant women and children less than 10 years of age need to be protected.
Efforts to limit the scale and spread of the disease will have to be continued by strong implementation of containment strategies by the states
The states cannot lower their guard and need to keep on implementing effective surveillance and containment strategies.