Recently, the National Centre for Disease Control (NCDC) conducted a sero-surveillance study for Covid-19 in New Delhi. The NCDC is under the administrative control of the Directorate General of Health Services in the Union Ministry of Health and Family Welfare.
About Sero-surveillance
Sero-surveillance is a method that aims to determine the prevalence of a disease in a population by detecting the presence of specific antibodies against the virus. This technique can be used to evaluate if a person has developed immunity to certain diseases. Sero-surveillance acts as an indicator of past infections that triggered an immune response but does not serve to detect active infections.
Testing Methodology
In this study, the Sera (part of blood) samples were tested for Immunoglobulin G (IgG) antibodies and for signs of Covid-19 infection using Covid Kavach ELISA kits approved by the Indian Council of Medical Research (ICMR). IgG is an antibody type that develops in most Covid-19 patients around two weeks following infection and remains in the blood post-recovery. ELISA, or Enzyme-Linked Immunosorbent Assay, is a test employed to detect and measure antibodies present in blood.
The Study’s Coverage
This sero-surveillance study was carried out from the 27th of June until the 10th of July 2020. During this period, the city was recording over 3,000 cases each day. A total of 21,387 samples were randomly collected across the 11 districts of the capital and divided into two groups: those younger than 18 years and those older.
Study Results
The results of the study indicated that 23.48% of the surveyed individuals developed IgG antibodies. This suggests that they were previously exposed to SARS-CoV-2, the novel coronavirus responsible for Covid-19, with a large faction not showing any symptoms (asymptomatic).
Government’s Response
The government views the study’s findings as an affirmation of its proactive efforts to limit the spread of Covid-19. The fact that only 23.48% were infected, shows that strategies like prompt lockdowns, effective containment and surveillance measures, contact tracing and tracking, coupled with residents’ compliance, were beneficial.
Challenges Ahead
Despite these positive results, approximately 77% of the population remains vulnerable to contracting the virus. Containment measures must continue with the same rigour. Non-pharmacological interventions such as physical distancing, using face masks, maintaining hand hygiene, promoting cough etiquette, and avoiding crowded places are still crucial.
Potential Concerns
One significant concern is that the seropositivity rate of 23.48% cannot be extrapolated over the entire population of Delhi. In addition, there is limited scientific data available about the body’s level and length of immunity after testing positive for Covid-19.
Past Sero-surveillance Studies
In April 2020, ICMR carried out a pilot sero-survey across 83 districts in 21 states. The preliminary results, currently under peer-review, propose that 0.73% of the general population might have been infected, with urban areas showing a higher prevalence of around 1.09%.
Looking Forward
The data gathered from this study will be instrumental in guiding future disease control programmes. These types of scientific studies are extremely important and need to be periodically conducted to learn lessons from the past.