The second serological survey conducted in Delhi between August 1 and 7 has found that 29.1% of the city’s population has developed antibodies against the coronavirus disease (Covid-19), state health minister Satyendar Jain said on Thursday. The survey results also showed the prevalence of antibodies among women was more (32.2%) compared to men (28.3%).

The findings of the second survey show that the prevalence of antibodies among the people has increased by over 6 percentage points when compared to the first survey held between June 27 and July 10. As many as 22.86% of people were earlier found to have developed antibodies against Sars-CoV-2 that causes Covid-19. In the first survey, samples were collected from 21,387 people, whereas, in the second round, 15,000 samples were collected. Jain said the third round of the survey will begin from September 1 and would go on for a similar duration as earlier.

According to the second survey, prevalence of antibodies among those aged less than 18 was 34.7%, and 28.5% for those between 18-50. For those above 50, it was 31.2%.

Government officials said the latest findings that those aged under 18 were found to have the maximum antibodies compared to other age groups would play a crucial role in the Delhi government’s decisions on opening schools and colleges. Chief minister Arvind Kejriwal, in his Independence Day speech on August 15, said that the government will not open schools until it is fully convinced about the city’s Covid-19 situation.

Giving the district-wise break-up, the health minister said the southeast district has seen the biggest increase in people developing antibodies. The lowest increase was seen in northeast Delhi, which once had the highest number of Covid-19 cases.

Developing antibodies means a person contracted Covid-19, recovered, and subsequently developed them against the disease. “Antibodies are found in high numbers anywhere between 3 and 8 months since the recovery of a Covid-19 patient. In the process, the person also develops T-cells because of which the chances of contracting Covid-19 again become extremely low,” Jain said.

The report showed the southeast district has seen a maximum increase in the prevalence of antibodies among people when compared with the findings of the first and the second surveys. It was earlier 22.12% and this time it was found to be 33.2%. This is followed by the south district–from 18.61% to 27.2%. But, after the southeast district, the areas with the highest prevalence of antibodies among people are north district (31.6%), followed by central district (31.4%).

In the southwest district, 16.3% of the people have been found to have developed antibodies, which is the lowest of all the 11 districts in Delhi. The second-lowest was the New Delhi district (24.6%).

A day after the high court directed the Delhi government to do a comparative analysis of the two serological surveys conducted in Delhi so far, the health minister on Thursday said that the government would do the same.

When asked about a possible second wave, Jain said, “We had expected that in the second sero survey the seroprevalence would increase considerably. But it has increased by around 6-7% since July. So, Delhi is heading towards herd immunity, but experts say that should be at least 40%. We cannot rule out a second wave because only yesterday India saw the highest ever spike in daily fresh Covid-19 cases.”

Jain said Delhi has a population of around 20 million and the findings of the latest survey suggest that around 5.9 million have contracted the Sars-Cov-2 virus and recovered from the disease. “It is relieving to know that around 29% of the city’s population has recovered after being infected by the coronavirus. On the other hand, 71% of people in Delhi have not developed antibodies, which means that they are still vulnerable,” he said. “The people of Delhi are being very careful in taking precautions against Covid-19. So, this is a very positive development. It shows that the Covid-19 infection numbers are no longer rising exponentially in Delhi.”

Jain said there was a time when the cases in Delhi were increasing by 4,000 daily and the positivity ratio was 30%. “It is also reassuring to see that the positivity rate in Delhi has reduced to nearly 7%, which is much lower than the national average. The situation in Delhi is improving.”

Charoo Hans, a former head of the microbiology department at Delhi’s Ram Manohar Lohia Hospital, said if 71% of people are still vulnerable, it is quite a high number. “It suggests that the government should continue with its efforts on aggressive testing, contact tracing, surveillance, isolation, and providing good treatment. It also suggests that people should continue ensuring strict compliance with social distancing, wearing masks, washing their hands frequently, and following respiratory etiquettes. There is no room for any complacency.”