Seropositivity higher in non-slum areas
The first and second serological surveys in Mumbai, to ascertain the prevalence of antibodies, were conducted in July and August 2020. The third was conducted in March across all the 24 civic wards, which showed the presence of antibodies in 36.3% of the total 10,197 samples. Results of the third survey showed an increase in seropositivity rate in non-slums as compared to slums. The sero survey in slum areas showed seropositivity at 41.6% as against 57% and 45% in last July and August, respectively. In non-slum areas, the seropositivity was found in 28.5% samples (which increased from last July and August’s 16% and 18%), making the population more vulnerable to Covid-19 during the second wave.
Dr Lancelot Pinto, pulmonologist, Hinduja Hospital, said, “The fact that most of the cases in the second wave were in highrises possibly suggests two things— the rates of re-infection were low or, most of the infections were likely in individuals who hadn’t encountered the virus in the first wave, and were therefore vulnerable.”
Dr Ravikant Singh, founder, Doctor For You, said natural antibodies produced in the first wave is still circulating among slum dwellers, making their immunity stronger to fight the virus. “In the second wave, the mutation of the virus made the infection more transmissible. This could have had severe repercussions in the denselypopulated slums. But I assume that many who had already been infected once, have natural antibodies against the virus, and hence, have reduced risks of getting infected during the second wave. We however need to understand that it is just a temporary shield,” said Singh.
Mass immunisation drives are therefore the need of the hour before the natural antibodies produced in the body become weak, said civic officials. “Antibodies remain in the body for four-six months. There is strong likelihood that once the slum population loses them, we could again see the virus spread through slums if there is another wave, unless we can catch up on vaccinations,” said Walunj.
Dr Pinto suggested that prioritising vaccination for those in areas with low seroprevalence, especially among high-risk individuals, would possibly be a high-yield strategy. “We need to also conduct regular seroprevalence studies coupled with whole genome sequencing to identify vulnerable populations and variants of interest before they spread rapidly,” he said.
Amita Bhide, dean, school of habitat studies, Tata Institute of Social Science (TISS), who has conducted several studies in M-east ward during the second wave, said the vaccination drive is still lagging in slums.
“The priority has been middle and high-class [groups] as the infection rate among them was high. As vaccination in slums is facing a setback, there is a need to bring the drive to people’s doors. Individuals in slums are still sceptical about the need for vaccination. Hence, the civic body also needs to focus on awareness,” said Bhide.
The Covid-19 containment proactive strategies not only helped BMC in controlling cases in slums, but their ‘Dharavi model’ also bagged them national fame and appreciation.
Through door-to-door surveys at slums, BMC created a health map that helped diagnose Covid patients faster and maintain a record of high-risk patients who were immediately isolated in Covid Care Centres (CCC). “We followed three strategies in slums— test, isolate and treat. Other than RT-PCR (reverse transcription polymerase chain reaction), we have been conducting rapid antigen tests on the floating crowds in slums. In Dharavi, we have also started mobile van testing facilities,” said Suresh Kakani, additional municipal commissioner. Growing awareness among slum dwellers also helped curb transmission from residential buildings. “The first wave has taught slum dwellers lessons that helped them survive the second wave. They were extra careful even while working in buildings. The question that now remains is how safe will slums be in the third wave,” said Bhide.