PUNE: A serological survey in Pimpri Chinchwad found history of Covid-19 in 34% of 5,000 people tested.
The study, the largest so far in the Pune Metropolitan Region, surveyed residents of slums and apartments from all eight PCMC wards.
Antibody prevalence was high (35%) among adults in the 51-65 age group. They were followed by the 12-18 age group, which had a seropositivity of 34%. Citizens in the age groups of 31 to 50 and 19 to 30 also showed considerable antibody prevalence, of 31% and 29% respectively.
And despite many of them staying home for months, 28% of senior citizens in the twin towns (above 66 years of age) showed they had come in contact with the virus at some point in time.
The survey also proved the virus takes advantage of household crowding. For example, 75% of residents from the slums of Pimple Nilakh gaothan, Trimurtinagar and Vinayaknagar had antibodies. But some high-income residential pockets of Sambhajinagar and Keshavnagar had the lowest prevalence of just 4%.
Experts said the high prevalence means there are now fewer susceptible people in PCMC limits — a factor they said could reduce the impact of a second wave, if it comes.
Sero surveys check blood samples for a specific class of SARS-CoV-2 antibodies called immunoglobulin G or IgG that appear within two weeks of infection. These antibodies do offer some immunity, even if the duration of that protection is under debate. And as per epidemiological theory, if 25% of a population has antibodies, the impact of subsequent infection waves could be much lower. “This survey has shown where people are most vulnerable to a second wave, if it comes,” an official from the PCMC’s health wing said.
A similar survey by the PMC in August had come under criticism for its low sampling — 1,664 people from only five high-incidence zones. Experts said the study was just too small for a city with an estimated population of 35 lakh. But does the presence of IgG antibodies mean resistance to Covid-19?
In an interview, virologist Priya Abraham, director of the National Institute of Virology, had said quantity matters too. “It (immunity) is largely dependent on concentration of antibody levels in the blood — called ‘antibody titer’,” she said.