Sero-surveys may be key to understanding Covid-19: BMC

A health worker collects a swab sample of a passenger at Dadar station. File pic

With instances of people contracting COVID-19 even after getting both vaccine doses and a bigger portion of daily cases still coming from high-rises, people have several questions about the ongoing pandemic. And, the BMC thinks the answers may come from sero-surveys. The most prominent question is if and when the third wave is coming.

While the BMC, on Monday, told the Bombay High Court that it does not apprehend a third wave in the city as the vaccination drive is going smoothly, civic officials are sceptical to announce the same in public.

Swab samples collected from passengers at Dadar station. File pic

The latest sero-survey, which was conducted in August, revealed that 87 per cent of the respondents had antibodies. Of the people who are fully vaccinated, 90 per cent had antibodies while the figure stood at 80 per cent for those without any dose of vaccine.

However, the BMC did not carry out quantitative tests which check the level of antibodies; so, it feels multiple sero surveys after intervals will be important to understand the progress of the virus and the pandemic better.

Human body produces antibodies when it is infected or it has received a vaccine. Unlike older antibody tests which detect whether antibodies are present or not, quantitative tests can tell the level of antibodies in the blood.

"We didn't conduct quantitative tests to check levels of antibodies in the last serosurvey. In fact, there isn't any confirmed threshold level of antibodies that one needs to be protected [against COVID-19]. So repetitive sero-surveys are a better way to analyse the situation and act accordingly," said Suresh Kakani, additional commissioner of BMC.

The civic body also conducted a study in July to find out the reason behind why some wards reported a high number of COVID-19 cases during both waves despite having less population while some others reported higher fatality rates. However, it was inconclusive.

"The study reported multiple reasons such as some wards conducted more tests, some have higher population, some wards registered more cases but have fewer fatalities, while some have a high test positivity rate. No specific reason was found," said an official from BMC.

87
Percentage of respondents who were found with antibodies