On the heels of the second sero survey findings that showed a decline in sero prevalence in slum areas, random tests will be conducted to assess the kind of antibodies generated among the surveyed people.
The Brihanmumbai Municipal Corporation along with Tata Institute of Fundamental Research (TIFR) will compare the presence of two antibodies— anti-spike antibody RBD and anti-nucleocapsid antibodies. It is largely seen that anti-nucleocapsid antibodies are induced earlier but they do not last long, while anti-spike RBD antibodies, which have more neutralising power against viruses, are generated a little late but potentially stays longer.
Detection of virus-specific antibodies becomes important to understand the infection prevalence and the course of the immune response.
In the second sero survey, covering 5,384 people, blood samples were tested for anti-nucleocapsid antibodies.
Now, randomised selection of these samples will be done to test for anti-spike antibodies to assess their prevalence in the population. The second sero survey in mid-August found a decline in the percentage of slum population exposed to SARS-CoV-2 from 57 to 45 per cent since July, when the first round of the survey was held. Epidemiologists have pointed towards “antibody decay” as possible reasons for the decline in sero prevalence hinting that the infection had spread in slums earlier than non-slums, and hence slum population developed antibodies earlier.
Professor Ullas Kolthur from TIFR said, “Sero prevalence measures antibody levels and hence provides an estimate of exposure to infection, but this could vary depending upon the levels of antibodies produced against one or the other viral proteins. While the prevalence estimates from our study is based on nucleocapsid antibodies, we are currently measuring the presence of RBD antibodies in a subset of the samples.”
This, Kolthur said, was important since the extent to which these antibodies are produced and their persistence seem to be different. “This was in our original design and our ongoing comparative studies will help us check if prevalence, as measured by RBD antibodies, will likely change,” he added.
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