Sero-survey Suggests Nearly 23% of Delhi Could be Affected by COVID But Experts Say Far From Herd Immunity

It showed that 20 per cent population in eight of the 11 districts in the national capital have developed antibodies against COVID-19. The survey also indicated that a large number of infected people remain asymptomatic.

New Delhi: Delhi’s sero-prevalence study has found that around 23 per cent of the people tested had an exposure to the novel coronavirus in the city, which has several pockets of dense population, the Union Health Ministry said on Tuesday. The study was conducted from June 27 to July 10 by the NCDC in collaboration with the Delhi government and involved testing 21,387 samples.

It showed that 20 per cent population in eight of the 11 districts in the national capital have developed antibodies against COVID-19. The survey also indicated that a large number of infected people remain asymptomatic.

Director of the National Centre for Disease Control (NCDC) Dr Sujeet Kumar Singh said the remaining 77 per cent are still vulnerable to the viral disease and containment measures need to continue with the same rigour.
NCDC Director Singh said, “When the prevalence was adjusted against the sensitivity and specificity of the ELISA test kits, the prevalence in Delhi was found to be 22.86 per cent and this is an adjusted figure… Eight of the total 11 districts have more than 20 per cent sero-prevalence.”

However, the national capital is still far from herd immunity against the coronavirus, the experts later said on the serological survey. The experts also cautioned against lowering of guard despite a fall in the number of COVID-19 cases reported on a daily basis in the national capital and warned against the possibility of a second peak.

After analysing the findings of the study, virologist Dr Shahid Jameel said Delhi is still far from developing herd immunity and the infection has spread rapidly.

Explaining the findings, he said if a 23.5-per cent seroprevalence is seen in Delhi, for a population of 1.87 crore, this amounts to 44 lakh infections. Since the national capital has so far witnessed 3,663 deaths due to COVID-19, the infection fatality rate is 0.08 per cent, which is similar to the first seroprevalence study conducted by the Indian Council of Medical Research (ICMR) in April.

“This tells me three things — the infection has spread quite fast, there is no mortality rate reduction since April-end and we are still far from herd immunity.

“Delhi has so far conducted 8.3 lakh COVID-19 tests. If 20 per cent is symptomatic out of 44 lakh people, there would be 8.8 lakh people with symptoms. But if only one positive is picked in 10 tests, we are even missing symptomatic people and are definitely under-testing even those with symptoms,” Jameel told PTI.

(With agency inputs)