BENGALURU: The Karnataka Health and Family Welfare Department have commenced the second serological survey across the 30 districts of the state as well as eight zones of Bengaluru on January 25 to assess the exposure of the population to Covid-19.
A serological prevalence survey involves drawing blood samples to detect whether an individual has been exposed to the infection in the past and whether he or she has developed Immunoglobulin G (IgG) antibodies to combat the infection.
The first survey done in September found that 16.4 per cent of the 16,585 people surveyed had developed antibodies and 12.7% had an active infection. The survey — that included people who had Covid-19 infection (prior to the survey) and those who had active infection during the survey — found an overall prevalence of 27.3 per cent in Karnataka.
According to health officials, the sample size from each district has been increased to 1,500 compared to 400 studied in the first survey. This time, the department intends to cover 35,000 people belonging to high, moderate and low-risk categories.
“The survey began on Monday and will continue for the next 10 days. Blood samples will be collected in 30 districts and eight zones of Bengaluru. The survey is expected to be completed within the next 10 to 15 days,” said Dr Ravi, former head of the Department of Neurovirology at NIMHANS and also member of the State’s Covid-19 Technical Advisory Committee.
Dr Manjunath, Director, Jayadeva Institute of Cardiology, said the results of the second survey would help us to know whether the state was heading towards herd immunity or not. “We had expected Karnataka to witness a surge in the number of cases after major events like the bypolls, GP elections, Dasara, Deepavali and Christmas where we saw huge gatherings and violation of Covid-19 norms. However, there was no surge in cases ... this could also be due to the fact that a large extent of the population could have already been exposed to the virus. The second survey will help us to determine this,” he added.
According to experts, a population is said to have attained herd immunity if 50 to 60 per cent of the people are found to have developed anti-bodies during a seroprevalence survey. Herd immunity implies that in any set of people in a community, after becoming affected by the virus, a lot many of them become immune to it on account of anti-bodies developed in response to it.
And, hence, such people become a protective layer between the infected person and the unaffected people, thereby breaking the chain of viral transmission. “The State government must conduct another round of serosurvey after this to determine the extent of the spread of Covid-19,” Dr Giridhara Babu, Senior Epidemiologist and Task Force member, said.