India / Delhi's 3rd sero-survey finds 25% population exposed to COVID-19

New Delhi: The third Covid-19 serological survey in Delhi, conducted last month, has found coronavirus antibodies in 25.1 per cent of the participants. 

The seroprevalence detected in the survey, whose results have been accessed by ThePrint, is lower than that found in August — 28.36 per cent. Experts say it could be because of many reasons, from survey limitations to the disappearance of Covid-19 antibodies after a certain amount of time. The first serosurvey, in July, had found a seroprevalence of 22.83 per cent. 

The latest serosurvey report was submitted in the Delhi High Court Wednesday. This, after the court asked the Delhi government, at a hearing on 16 September, to submit the report in court before making it public, unlike the previous two serosurveys. 

A total of 17,409 samples from each of Delhi’s 11 districts were studied in the survey, which took place between 1 and 15 September. The August and July rounds involved 15,046 and 22,853 samples, respectively. 

The study was based on a multistage random sampling method where participants from each district were selected on the basis of seroprevalence detected in the August survey — that is, participants were selected from areas where the seroprevalence was found to be high in the last exercise.

The second and third surveys have been conducted by the Delhi government-run Maulana Azad Medical College and Hospital, while the first was carried out by the National Centre for Disease Control (NCDC), which is overseen by the Union Health & Family Welfare Ministry.

Highest and lowest prevalence 

The third serosurvey found the highest prevalence of antibodies in Northwest district, at 31.8 per cent, while the lowest was detected in Northeast at 12.2 per cent. 

In the August survey, the highest prevalence was found in Southeast district at 33.2 per cent, and the lowest in Southwest at 17.4 per cent. In the first serosurvey, the highest prevalence was found in the central district, 27.8 per cent, with Southwest again at the other end of the spectrum with a seroprevalence of 12.9 per cent. 

The latest survey has found seroprevalence of above 30 per cent in only three districts — Northwest, East (31.1 per cent) and South (30.1 per cent). 

The others, in descending order of seroprevalence, are Shahdara (28.7 per cent), West (27.9 per cent), Southeast (27 per cent), North (24.1 per cent), Central (21.7 per cent), New Delhi (18.6 per cent), Southwest (14.6 per cent). 

Highest prevalence among adolescents

Like in the August exercise, the September survey, too, has found the highest prevalence among the 5-17 age group, at 27.2 per cent, followed by the 50-and-above age group, where prevalence was recorded at 26 per cent. 

The 18-49 age group recorded the lowest seroprevalence at 23.5 per cent. In the August survey, too, the 5-17 age group recorded the highest seroprevalence at 31.1 per cent, followed by the 50-and-above age group at 30.7 per cent. The 18-49 age group recorded the lowest seroprevalence in the previous survey, too, at 26.5 per cent.

Higher prevalence among women

In another finding similar to the August survey, the study found a higher seroprevalence among women than men across all three age groups. The highest prevalence was found among women in the 50-and-above age group at 28.5 per cent, followed by the 5-17 age group, with a seroprevalence of 27.9 per cent, and the 18-49 age group, at 24.7 per cent.

Among men, seroprevalence was found to be highest in the 5-17 age group, at 26.7 per cent. This was followed by the 50-and-above age group, where seroprevalence was 23.9 per cent, and the 18-49 age group, at 22.5 per cent.

The survey also sought to study exposure trends with respect to the participants’ socioeconomic status. Covid seroprevalence, the survey found, was higher among those on the lower end of the socioeconomic spectrum, with per capita incomes of less than Rs 5,000. Among the participants with an income of less than Rs 5,000, an estimated 26.1 per cent had had exposure to the novel coronavirus, as opposed to 20.5 per cent among those with incomes above Rs 5,000. 

The survey also found a lower seroprevalence in planned colonies in comparison to resettlement colonies, urban slums, unauthorised settlements — 22.9 per cent against 25.9 per cent.