Karnataka still far from natural Covid immunity due to waning antibodies, shows study

BENGALURU: The second Covid-19 serosurvey conducted in Karnataka has revealed lower levels of Immunoglobulin G (IgG) seroprevalence due to antibody waning. 

The IgG is the most common type of antibody found in the blood. The estimated IgG prevalence at the end of the second survey was just 15.6 per cent and is markedly lower than the estimated total infection of 27.7 per cent at the end of the first serosurvey.

“The sentinel-based population survey helped identify districts that needed better testing, reporting and clinical management. The state was far from attaining natural immunity during the survey and hence, must step up vaccination coverage and enforce public health measures to prevent the spread of Covid-19,” concluded the statewide survey carried out between January 25 and February 18 across 290 health care facilities spread across Karnataka.

Interestingly, the estimated active prevalence was zero per cent across all districts. The subsequent rise in infection from March to June may be due to a combination of effects ranging from immunity waning to the emergence of the B.1.617 variant and its sub-variants, the study noted. 

SEROPREVALENCE HIGHEST IN MYSURU

“A longitudinal study to assess the clinical sensitivity of the test kit, in view of antibody waning, was also conducted. We recalled a few participants who had tested positive from the first serosurvey and conducted the antibody test. Of them, 38.9% of participants had detectable IgG, based on an ELISA test which used the whole cell antigen instead of the more specific recombinant nucleocapsid or spike protein antigens. Based on the longitudinal study, we were able to infer that Karnataka’s Covid-19 burden was between 26.1% and 37.7% at the time of the survey,” the authors of the study told TNIE.

The study was conducted on those aged 18 and above and they were subjected to RT-PCR and antibody tests. The prevalence was highest in Mysuru (33.6%) followed by Mandya (31.9%), Kodagu (27.1%), Chamarajanagar (22.6%) and Kolar (20.8%).