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28.3% of Delhi’s population now exposed to Covid, shows second sero survey, up from 23.4%

Delhi’s exposure now is nearly 5 percentage points above that detected in the previous serological survey conducted between June end and early July.

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New Delhi: Around 28.3 per cent of Delhi’s population has now been exposed to Covid-19, according to the latest serological survey conducted in the capital, ThePrint has learnt.

This is nearly 5 percentage points above the exposure detected in the previous serological survey, conducted between June end and early July.

The fresh survey was conducted earlier this month and its results are based on 15,289 randomly-collected blood samples. The findings of the survey, to be officially released later this week, were shared with ThePrint by officials of the Delhi government.

Serological surveys are an exercise aimed at detecting the true exposure of a population to a disease. They involve testing blood samples for antibodies and thus help detect even those people who may have recovered from the disease on their own without requiring medical assistance. In the case of Covid-19, this would include asymptomatic patients who unknowingly contracted and recovered from the disease. 

Serological surveys are important since they factor in cases not accounted for in the testing figures.

Sources in Delhi Health Minister Satyendar Jain’s office confirmed the results of the new survey, which was overseen by the AAP government. The results were discussed Tuesday at a meeting held between the Delhi principal health secretary, dean of the Maulana Azad Medical College (MAMC), which is compiling the findings, and other senior health department officials.

ThePrint approached Delhi Principal Health Secretary Vikram Dev Dutt for a comment on the new serological survey, but received no response despite several calls and text messages.

Also Read: Modelling, testing, sero survey, vaccine — 4 lessons India learnt from 4 months of Covid

‘Exposure highest in South-east Delhi’

In the first serological survey conducted last month, 23.48 per cent of Delhi’s population was found to have been exposed to Covid-19. It was based on 21,387 samples collected between 27 June and 4 July.

While the first survey was conducted by the central government’s National Centre for Disease Control, the new exercise was under the Delhi government — part of a plan to conduct sero surveys in the capital every month. It was held between 1 and 7 August.

The blood samples were processed at 19 state-run — Delhi’s and central — laboratories, including those at RML Hospital, Hindu Rao Hospital, RGGHS, Institute of Liver and Biliary Sciences, Vallabhbhai Patel Chest Institute, VMMC, & Safdarjung Hospital, GB Pant Hospital, AIIMS Delhi among others. The results were then compiled by the MAMC. 

A senior member of the MAMC team that compiled the results, requesting anonymity, said Delhi’s South-east district had maximum sero-prevalence at 33.2 per cent, while South-west had the lowest at 16.3 per cent. 

The breakup for the remaining districts will be shared when the results are officially declared, the MAMC official said. South-west Delhi also had the lowest seroprevalence in the July survey, at 12.95 per cent, but the South-east district, at 22.12 per cent, didn’t have the highest. It was the central district that was found to have the maximum seroprevalence at 27.86 per cent. 

Once a person has developed antibodies against Covid-19, they face a relatively lower chance of contracting the infection again. In this light, serological surveys can also indicate whether a population has achieved herd immunity.

Herd immunity is when a vast section of the population has gained immunity to a disease — by exposure or vaccination — and marks a point where the chain of transmission can be considered broken. 

Speaking to ThePrint, MAMC Dean Nandini Sharma said one cannot conclude yet if there is herd immunity in Delhi. 

“The data is huge so we are still analysing a couple of things before coming to such major conclusions,” Sharma added.

As of Tuesday, Delhi had registered 1,54,741 Covid-19 cases and 4,326 deaths.

Also Read: Pune’s first sero survey shows over 51% infected by Covid in 5 high-incidence areas


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