TOI had reported on January 26 that over 50% people in the city may have developed antibodies, as per the fifth sero survey, and that could be the reason why cases were dipping consistently.
Delhi’s health minister Satyendar Jain said it was up to experts to say whether the city had developed herd immunity but it was surely getting there. He urged people to keep following Covid-appropriate behaviour and not let their guard down. Experts say seroprevalence in 50%-60% or more in a population indicates herd immunity because the chain of transmission is broken and the spread of the disease diminishes. Dr Sanjay Rai, professor of community medicine at AIIMS, feels the city is unlikely to witness another major outbreak now.
The South East district has the highest seroprevalence of 62.2% while North has the lowest at 49.1%.
Survey: Women have more seroprevalence than men
All the previous rounds of sero surveys had revealed significant variations in districts with the densely populated ones reporting higher seroprevalence in some surveys and lower in some. In the current fifth round, all the districts have reported more than 49% seroprevalence.
This was the country’s largest sero survey for which 28,000 samples were collected from 272 wards of the capital in January. Seroprevalence has doubled in just three months — the October round of the survey had detected antibodies in only 25.5% people.
The sero survey reveals that females have more seroprevalence as compared to males. The samples represented all sections of people, from those who live in slums to residents of affluent areas. Blood samples of participants, from 5 years to 50 and above, were collected between January 15 and January 23.
“This was the largest sero survey in the country and no other state has conducted a sero survey on this scale before. We had collected 28000 samples, 100 samples each from all municipal wards,” said Jain at a presser.
Delhi conducted the first sero survey in July followed by one each month. The seroprevalence was 22.8% in the first survey, 28.7% in second, 25.1% in third and 25.5% in the fourth. Later experts asked the government to put a bigger gap between two surveys. “The fifth survey was conducted after a gap of 45 days. A sixth will be carried out after a gap of 45 to 60 days,” said Jain.
“Covid cases have come down considerably and have been lower than 200 for the past 10-12 days. Positivity rate has been lower than 1% for the past one month. I want to request you to please wear a mask, despite fewer Covid cases, a declining positivity rate and fewer patients in hospitals. In the past three months, people of Delhi have carefully followed Covid-appropriate behaviour,” Jain said, adding that they need to do it for a few more months.
The director general health services, Dr Nutan Mundeja, said the sero survey was conducted along with Maulana Azad Medical College. “We used CLIA technology, which is more sensitive than ELISA and the samples have been tested at Institute of Liver and Biliary Sciences so that there is uniformity across the city,” she said.
Delhi is witnessing an alltime low in daily cases for the past few days and the number of active cases is at 1,265. The capital has conducted more than one crore Covid tests, out which 6.3 lakh were positive.