The results of a sero-prevalence study show that on an average, across Delhi, up to 23 per cent of the population has developed antibodies against Covid-19. This indicates that the population which is believed to have developed antibodies was silently infected and has now recovered.

A statement released by the Ministry of Health and Family Welfare (MoHFW) said that it had commissioned a sero-surveillance study in Delhi. The study was done by the National Center for Disease Control (NCDC) in collaboration with the Delhi State government, following a rigorous multi-stage sampling study design from June 27 to July 10, across 11 districts of Delhi.

Blood samples were collected from the selected individuals after taking written consent and then their sera were tested for IgG antibodies and infection using COVID KAVACH ELISA test kits approved by Indian Council for Medical Research (ICMR). The Health Ministry said that with 21,387 blood samples drawn it is one of the largest sero-prevalence studies conducted in the country using the ELISA testing.

The tests help in identification of presence of IgG antibodies in the general population. The quality of the kits used and their sensitivity as well as specificity though can affect the results and throw up some false positives.

The advantages

Anti-body testing repeatedly done over time i.e. sero-surveillance, generates important evidence for assessing the spread of the pandemic, the Health Ministry has stated. The study also indicates that a large number of infected persons remain asymptomatic.

“Nearly six months into the epidemic, only 23.48 per cent of the people are affected in Delhi, which has several pockets of dense population. This can be attributed to efforts taken by the Government to prevent the spread of infection including lockdown, containment and surveillance measures, including contact tracing and tracking, as well as citizen’s compliance to Covid appropriate behaviours,” the statement mentions.

Covid-appropriate behaviour includes wearing masks, maintaining safe distance, hand wash hygiene and avoiding crowded places.

“However, a significant proportion of the population is still vulnerable. Therefore, the containment measures need to continue with the same rigour. Non-pharmacological interventions such as physical distancing, use of face mask and cover, hand hygiene, cough etiquette and avoidance of crowded places must be followed strictly,” the statement says.