NEW DELHI: Around 23% of Delhi’s population had been infected with coronavirus till first week of July, a serological survey covering over 20,000 people across the Capital’s 11 districts between June 27 and July 10 shows. It also points out that a large number of infected people remain asymptomatic.
The findings of the survey, conducted by National Centre for Disease Control (NCDC) along with Delhi government, were released on Tuesday.
NCDC Director Sujeet Kumar Singh said the adjusted prevalence of IgG antibodies is 22.86% after taking into account sensitivity and specificity of the tests.
“Nearly six months into the epidemic, only 22.86 % of the people are affected. This can be attributed to the efforts taken up for preventing spread of infection through lockdown and other containment measures,” Singh said.
The results of the survey also indicate a significant 77% of the population is still vulnerable. “Containment measures need to continue with the same rigour. Besides, non-pharmacological interventions such as physical distancing, use of face mask, hand hygiene, cough etiquette must be followed strictly,” Singh said.
While a part of the population remains uncovered under the survey, the government maintained that the attempt has been to cover a large part of the population.
“RT-PCR test and Rapid Antigen Tests are helpful in the treatment of individual COVID-19 patients, while Antibody Detection Tests help assess the prevalence of infection in the community. It is natural that some people such as asymptomatic people are missed by any surveillance network we put in place, in this scenario, a sero-survey helps assess the prevalence of COVID-19 infection in the community,” Dr Singh said.
Of the 11 districts, eight have sero-prevalence of more than 20%. In central, northeast, and Shahdara districts have sero-prevalence of over 27%.
After seeing a daily rise over close to 3,900 cases in June, Delhi registered 954 fresh cases on Tuesday.
The health ministry emphasised that increased testing led to early identification helping contact tracing and isolation of positive cases has resulted in decline in transmission.
In the first week of June, when Delhi was conducting an average 9,500 tests per day, the positivity was 37%. In July first week, the tests were increased to over 25,000 and the positivity rate has come down to 9%. It has now come down further, the government said.
“This gives us confidence in the strategy we have adopted. The disease was accelerating in Delhi but without taking any new restrictions but by bringing the same measures with more rigour we could control our numbers,” NITI Aayog member Dr VK Paul, who heads the empowered group on COVID-19 response and COVID-19 taskforce said.
Paul said the data collected through the sero-survey is “robust” and will be further used by the government for disease control.
On whether the declining curve of fresh cases in Delhi indicate that it is past its peak, Singh said : “We cannot say that yet because there is still a lot of population which is susceptible to the virus…the remaining 77% is still vulnerable and containment measures need to continue with the same rigour.”
An earlier sero-survey conducted by the Indian Council of Medical Research (ICMR) in containment zones showed sero prevalence of 34% in Ahmedabad and 9-11% in Delhi, Singh said.
Symptoms based screening and testing policy may not be able to assess the burden of infection in the community effectively. Hence, periodic sero-surveys are required to assess the extent of infection in the community, he added.