Karnataka far from natural immunity against Covid-19: Sero-survey

Karnataka was far from attaining natural immunity against the SARS-CoV-2 virus in January this year, and hence must step up vaccination coverage and enforce public health measures to prevent the spread of Covid-19, concluded the second serosurvey done in January-February this year, the results of which were finally published eight months later on a preprint server.

The study found antibodies in 15.6 per cent of the population and active Covid infection in just 0.5 per cent.

Statewide infection fatality rate (IFR) was estimated as 0.11 per cent, and Covid-19 burden estimated between 26.1 to 37.7 per cent.

The study of 41,228 participants across 290 healthcare facilities in all 30 districts of Karnataka was done among three groups of participants (low, moderate, and high risk).

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Epidemiologist and State Covid-19 Technical Advisory Committee (TAC) member Dr Giridhar Babu tweeted, "The study found lower levels of IgG seroprevalence (antibodies), mostly due to antibody waning. We found near zero prevalence of active cases during mid-February 2021. Karnataka was far from attaining population levels of immunity during the survey."

Another TAC member Neurovirologist Dr V Ravi, state nodal officer for genetic confirmation of SARS-CoV-2 virus, told DH, "One should remember that this survey was done when the first wave ebbed. The people who participated in the second round were those who didn't participate in the first round (in September last year). So, these infections are in addition to what we found in the first survey."

"The right interpretation is to add both results that gives us 42.9 per cent (27.3 per cent prevalence found from first serosurvey + 15.6 per cent from second survey)," he said.

Ravi explained that considering until January, only 43 per cent were exposed, this explains why we had a huge second wave because more than half of our population was not exposed.

"We need to do at least 1.2 lakh vaccinations per day and sustain high levels of testing. Now, we're waiting for the government clearance to do the third survey. This time the added variable will be the vaccination status of the participants and if it has any effect on the disease burden," he said.

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He pointed out that since the gap between both the rounds of serosurveys was more than three months, antibodies waned.

"This is why we called back participants from the first survey, and found that more than half of them did not have antibodies," he added.

Babu further added, "There was a subsequent surge seen in Karnataka due to a mix of alpha, and delta (variants) which was picking up speed in April, and a large susceptible population were infected."