Over 23% of Delhi’s population exposed to coronavirus, shows sero-survey results

More than 23% of Delhi’s 1.9 crore population showed evidence of past exposure to Sars-Cov-2, which causes the coronavirus infection, in almost six months and that a large number of infected people remain asymptomatic.

New Delhi: More than 23 % of Delhi's 1.9 crore population have been infected by Covid-19 whereas the remaining 77% are still vulnerable, a serosurvey conducted in the national capital has revealed.

"Nearly six months into the pandemic, 23.48 percent of the people are affected in Delhi, which has several pockets of dense population. However, a significant proportion of the population is still vulnerable. Therefore, containment measures need to continue with the same rigour. Non-pharmacological interventions such as physical distancing, use of face mask, hand hygiene, cough etiquette must be followed," said Sujit Kumar Singh, director of National Centre for Disease Control (NCDC).

Following directions from Union Home Minister Amit Shah, the Health Ministry has commissioned sero-survey study in Delhi to estimate the sero-prevalence for SARS-CoV-2 infection among general community of Delhi.

Serology (antibody) tests are largely used for surveillance among communities and can be used on people who have already been tested positive for the virus or even those who are asymptomatic.

The survey was conducted from June 27 to July 10 by NCDC in collaboration with the Delhi government.

The survey team formed for all 11 districts of Delhi, collected blood samples of more than 20000 individuals to detect the presence of IgG antibodies and infection using COVID Kavach ELISA approved by ICMR. Significantly, this was one of the largest sero-prevalence studies conducted in the country using ELISA testing.

While indicating that a large number of infected persons were asymptomatic, the survey reported that the prevalence of IgG antibodies was found among 23.48 percent population.

Singh said that RT-PCR and Rapid Antigen Test (RAT) were conducted to detect active infection of Covid-19 infection.

"Symptoms based screening and testing policy may not be able to assess the burden of infection in the community effectively, hence, periodic sero-survey are required to assess the eaten of infection in the community," Singh added.

Claiming that strict containment measures have attributed to a small percentage of infection in Delhi, Singh said, "This can be prevented to the efforts taken up for preventing spread of infection through lockdown and other containment measures."

"The disease in Delhi was accelerating till June. Then we followed best practices and it is contained," Niti Aayog member VK Paul said.

Dr. Rajesh Bhusan, the Officer on Special Duty (OSD) in the Health Ministry termed the findings of the sero-survey as an eye-opener in India's fight against Covid 19 pandemic.

He informed that from June 18 to July 21, as many as 3,63,172 people went through rapid antigen tests and out of which at least 23,000 people (6.33 percent) were found Covid positive. Interestingly, 2294 people who tested Covid negative in antigen test went under RT-PCR test again.

"As many as 348 people were again found Covid-19 positive following RT-PCR test," said Dr. Bhushan.

Meanwhile, the ICMR initiated sero-survey in containment zones in India has found that there is a 34% prevalence of Covid-19 in Ahmedabad, 35 % in Mumbai and Kolkata.

It is to be noted that 70% of the Covid caseload is from cities like Mumbai, Ahmedabad, Pune, Delhi, Kolkata, Indore, Thane, Jaipur, Chennai and Surat.