The Brihanmumbai Municipal Corporation (BMC) has now decided to conduct a third sero surveillance across the city ensuring every individual has developed antibody and immunity to fight the novel coronavirus. As part of it, the civic authorities have collected 12,000 samples from all age groups in Mumbai. The civic officials said the main reason to conduct the third sero survey is to gauge the percentage of population developed antibodies. However, the authorities have denied herd immunity.
Immunoglobulin-G (IgM) antibodies are produced by the immune system of the body in response to exposure to foreign elements like a virus. In sero survey, a group of individuals undergo blood tests to detect the presence of IgM antibodies. This helps identify the individuals, who were previously infected with the virus and have now recovered.
Last year, the civic body had conducted two sero surveys within a span of two months which revealed the population residing in slum areas had shown high sero prevalence as compared to the individuals residing in the high-rise societies. Moreover, recently the Indian Council of Medical Research (ICMR) has conducted sero surveillance which revealed 25 per cent of Indians developed antibodies against SARS-CoV-2 virus.
Suresh Kakani, Additional Municipal Commissioner, BMC, said the third round survey is being done to know the exact percentage of the SARS-COV-2 virus among the citizens. Once the study is concluded they will compare it from the last two surveys.
“The sample size will be high for this survey compared to the last two survey. This time we have collected 12,000 samples compared to 8,870 and 6,936 which were collected in the first two surveys respectively. The main reason to conduct this survey is to understand the infection rate amongst Mumbaikars ,” he said.
“There are a lot of people who were affected, but might not be detected. However, we are still seeing cases coming out, so the viral activity has not stopped," Kakani added.
Health experts said there was no comparison between the first and second sero surveys, as they only showed the exposure of the participants to the virus. Further, he felt there was a rapid decrease in antibodies, which would further decrease were citizens to adhere to Covid-19 protocol.
“We are nowhere near herd immunity and the sample size for the study is very small, so we cannot come to conclusions. The study only provides information about the spread of infection in the population and in order to learn about the actual prevalence of the SARS-Cov-2 virus, there should be a 70 per cent sample size with T-cell response,” he said.