The survey showed nearly 23 per cent had developed anti-bodies for the virus in Delhi(Representational)
A sero-prevalence survey in Delhi did not find antibodies against the novel coronavirus in the blood of 97 out of 208 people who had previously tested positive for COVID-19, with the National Centre for Disease Control saying it indicates that immune response generated by the virus could be "transient in nature".
The survey, carried out jointly by the Delhi government and the NCDC between June 27 and July 10, had used 21,387 samples and found that around 23 per cent of the people surveyed had an exposure to the novel coronavirus.
"Among surveyed population, 8 per cent...informed about testing (positive) for COVID-19. Of these, only 208 i.e 13.5 per cent were positive by RT-PCR and only 111 of 208 i.e 53.37 were found to be seropositive and 97 study subjects who were tested positive by RT-PCR were seronegative," the NCDC report says.
"The caveat of this finding corroborates with the current scientific knowledge that the immune response generated by SARS CoV 2 is probably transient in nature and need to further investigated though prospective cohort studies," it added.
Among other measures, the NCDC has also recommended sero-surveys in neighbouring cities, like Noida, Ghaziabad, Faridabad, Gurugram and Sonepat after assessing the epidemiological trends for exposure.
The survey showed nearly 23 per cent people had developed anti-bodies for the infection, said NCDC Director Dr Sujeet Kumar Singh had said when the results of this survey were announced.
However, the remaining 77 per cent are still vulnerable and the containment measures need to continue with the same rigour, Singh told a press briefing.
The survey was done to estimate the proportion of people exposed to coronavirus infection in the total population of Delhi and the number of people selected from each district for the survey is proportionate to the population of that area, Singh had said.
Delhi has a population of nearly 2 crore. Eight out of Delhi''s 11 districts have more than 20 per cent of sero-prevalence, he said.
After this, the Delhi government had done another round of survey from August 1-7, according to which anti-bodies against COVID-19 infection were found in 29.1 per cent of people surveyed in the national capital.
The prevalence of anti-bodies found in males was 28.3 per cent, and in females 32.2 per cent in August survey.
Sero-prevalence of antibodies against found in age group of less than 18 was 34.7 per cent, in 18-50 years 28.5 per cent, and 31.2 per cent in 50 years and above, in the exercise conducted last month.
Among other recommendations made by the NCDC, it said non-pharmaceutical interventions like physical distancing, use of appropriate face masks, use of sanitiser, etc., should be strictly implemented.
Repeat surveys may be needed to assess the sero-positivity trends, among the sero-positive individuals (prospective cohort study) for assessing the probable duration of IgG; case control study may also be undertaken to assess the protection conferred by IgG, it recommended.
The national capital had seen spurt in daily cases in the last several days and a steady rise in active cases since August 5.
Delhi on Tuesday reported its highest single-day spike in coronavirus cases in nearly two months. Government data shows Delhi reported 2,312 fresh coronavirus cases and 18 deaths in the last 24 hours, taking the total to over 1.77 lakh.
Meanwhile, the fresh round of monthly sero-prevalance survey in the national capital began on Tuesday, which will be carried out across the 272 municipal wards to analyse the COVID-19 situation in Delhi at a "micro-level".