Almost 50% in Karnataka were infected by August: sero study

Seroprevalence studies conducted in a random population are essential for measuring the spread of the Covid-19 pandemic. Researchers from the IDFC foundation undertook a statewide study in Karnataka in collaboration with the Centre for Monitoring Indian Economy.

Almost half of Karnataka’s population was infected with Covid-19 by August. A seroprevalence study indicated that at least 44.1 per cent of the population in rural areas of Karnataka and 53.8 per cent in urban areas were exposed to the coronavirus, and have therefore developed antibodies for the infection.

The IDFC institute, Mumbai, carried out a comprehensive Covid-19 seroprevalence study in Karnataka based on data collected from a representative sample of households in 20 districts of the state from mid June through August. It found that the state alone has 31.5 million Covid-19 cases with 44 per cent of rural and 54 per cent of the urban population affected.

Seroprevalence studies conducted in a random population are essential for measuring the spread of the Covid-19 pandemic. Researchers from the IDFC foundation undertook a statewide study in Karnataka in collaboration with the Centre for Monitoring Indian Economy. The study, funded by ACT Grants (India), was led by Professor Manoj Mohanan from Duke University, Professor Anup Malani from Chicago University, and Anu Acharya from Mapmygenome along with Kaushik Krishnan from the Centre for Monitoring Indian Economy.

The presence of antibodies in the blood typically suggests that people infected with a virus would gain immunity for some period of time. The new study, ‘Prevalence of COVID-19 In Rural Versus Urban Areas in a Low-Income Country: Findings from a State-Wide Study in Karnataka, India’ was published recently as a preprint in medRxiv.

According to researchers, among the two key reasons were rural areas experienced fewer restrictions on mobility and the release of the lockdown imposed in March was immediately followed by a large migration of daily labourers who lost their sources of income in urban centres returning to rural parts of the country.

The study sample was drawn from an existing, representative sample of a panel survey by the Centre for Monitoring Indian Economy’s Consumer Pyramids Household Survey (CPHS). The Karnataka Seroprevalence Study (KSS) draws a random sample from CPHS’s 9,717 households in the state separately for the urban and rural strata. The state has a population of roughly 64 million.

Adjusted seroprevalence across Karnataka implies, based on the government mid-year 2020 population estimates, that approximately 31.5 million residents have been infected, 96.4 times the 3,27,076 publicly reported cases as of August 29. Estimated RT-PCR positive proportions suggested that the pandemic was growing rapidly during August. The proportion of those testing positive on RT-PCR ranged from 1.5 to 7.7 per cent in rural areas and 4.0 to 10.5 per cent in urban areas, suggesting a rapidly growing pandemic.

Meanwhile, according to researchers, a total relaxation could lead to a spike in infections among such at-risk populations leading to further spikes in severe cases or mortality that will create a large burden for the healthcare system. Hence, as the government considers relaxing restrictions on economic activity, it is critical to continue efforts to promote mask wearing, hand washing, and communicating the significance of Covid-19 complications to individuals who are at risk. “Our findings underscore the need for larger scale studies across India that can provide estimates of seroprevalence at smaller levels of granularity and also study what happens to antibodies and t-cell immunity over time,” one of the researchers said.

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