Mumbai's BMC To Conduct More Sero Surveys Across The City

The current study needs to be further researched to evaluate the levels of exposure to COVID-19 and herd immunity

The country's richest municipal body, Brihanmumbai Municipal Corporation (BMC) has said that they plan to replicate its sero-surveys across the city to understand the spread of COVID-19 in the island city. These findings will help the civic body formulate policy changes while also understanding steps to achieve herd immunity.

On Tuesday, the BMC released the findings of its sero-survey that it conducted in three wards of Mumbai. The study which was divided into slum pockets and non-slum pockets showed a prevalence of 57% in the former and 16% in the latter. The interpretation of these findings suggest that more people in the slums have already been exposed to the virus.

Also Read: Mumbai Sero-Survey: 57% In Slums, 16% In Non-Slums Exposed To COVID-19 Virus

To understand whether these findings can be extrapolated to the city at large, BOOM spoke to three different stakeholders who collaborated on the study. Dr. Daksha Shah, deputy executive health officer, BMC stated that modelling and planning for recreating these sero-surveys in other wards is already underway.

Speaking about the BMC's approach of capturing differences between slums and non-slums, Dr. Ullas Kothur-Seetharam, Professor, Department of Biological Sciences, Tata Institute of Fundamental Research siad "This helps us understand whether these findings can be replicated across the city or tailor it for changes."

R-North (Dahisar), M-West (Chembur), and F-North (Sion, Matunga) wards were selected as they represented the growth rate in the 24 wards of the city. Dahisar represented areas with low cases, Chembur represented areas with moderate cases, and Sion, Matunga represented wards with higher cases. The current findings provide an estimate and an overview of the spread across the city, say the officials.

Dr. Jayanti Shastri, microbiologist at Nair Hospital who is also running the Molecular Diagnostic Laboratory at the civic-run Kasturba Hospital believes that these findings will be strengthened with the second round that will be conducted in the same areas in August.

An important point that Dr.Seetharam highlighted was that this survey was conducted in areas that were not containment zones. A second round would help in identifying higher confidence and lower variance, further boosting the study. To this, Dr. Shah added that these findings helped in understanding the level of asymptomatic infections and the extent to which people have been exposed to the virus.

This survey, however, did not ascertain if any participants had earlier tested positive for COVID-19 through the standard RT-PCR tests. The samples were collected randomly from both the slums and non-slums.

Antibodies For COVID-19

Dr. Shastri discussed that there was no cross-reactivity in these findings. Cross-reactivity is when one antibody can bind to more than one pathogen. The BMC used Abott's Chemiluminescene assay to ensure that the screening for presence of antibodies was carried out by kits of the best quality.

"All our results are truly positive for COVID-19 proving that this proportion of the population has been exposed to the virus," Dr. Shastri added. These findings, however, do not prove that these antibodies neutralize the effect of SARS-CoV-2.

Several studies have been stating that the antibodies tested by these kits by Abbott and Roche could wane in a few months' time. New York Times reported that these machines test for a different marker on antibodies. Instead of the spike protein, these test kits test for an N protein that is seen to decline faster.

How To Interpret The Findings

Factors contributing to the spread of the SARS-CoV-2 as well as its impact on people from different age groups and sexes can be studied through such surveys. They also assist in bringing fresher perspectives while formulating policy changes, the experts believe.


- Second Round of sero-survey in these same areas to validate the findings

- Planning and modelling to replicate the sero-survey in other wards in the city is underway

- No cross-reactivity, ie. all the tests are true positives showing the extent to which this virus has spread

Watch the full video here.

Updated On: 2020-10-08T11:38:30+05:30
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