BENGALURU: A sero surveillance study in Bengaluru’s 24 slums have shown a seropositivity rate of 20.3 per cent during the second wave. The study suggests that a large proportion of the population may remain either susceptible to SARS-CoV-2, or might have waning antibodies from previous infections. A rapid community survey to assess the Covid-19 burden in slums was planned as the number of cases reported from slums during the onset of the second wave, was low.
The study was done collaboratively by RGUHS, BBMP, TAC, GoK and Karnataka Association of Community Health in slums attached to 11 medical colleges and Nimhans. According to Dr Ranganath, professor and HOD, Bangalore Medical College,
“The study shows one in five subjects was seropositive to SARS-CoV-2, and one in 15 individuals had active Covid-19 infection.” Dr N R Ramesh Masthi, Professor and Head of Community Medicine, KIMS, who was part of the survey, said the study was done between April 15 and 22, when the second wave was just beginning. “The survey showed an infection to case ratio of 3:1,” he explained.
The survey also found that core areas of BBMP, which make up the Central Business District, showed seropositivity of 24%, and outer areas showed 12.5%, indicating that the suburbs were less exposed. This means the CBD had many people who were already infected during the first wave or second wave, and had developed antibodies, he added.
The sample size was 728, while each medical college had to sample 60 people from each slum. Interestingly, the study also found that cellular immunity could be still playing a role, and preventing them from testing positive even when their IgG immunity was waning. “The role of cell mediated immunity in protection against SARS-CoV-2 and waning of antibody titers over time, needs to be looked at from these findings. However, we are not able to measure cellular immunity as of now,” explained Dr Masthi.
Meanwhile, it was observed that many of these people didn’t follow social distancing or maintain hygiene, and only 1.55% was vaccinated with two doses. Dr CN Manjunath, member of Covid-19 Technical Advisory Committee (TAC) said, “There is a high possibility of them getting more affected during the third wave. They should speed up vaccination in these slums,” he said.
However, the study has some limitations, explained Dr Giridhara Babu R, another TAC member, who was part of the survey. He said this is a very small sample and the study will need more repeat surveys to know the exact findings.