New Delhi: On April 29, Harvard University Professor S.V. Subramanian and K.S. James of the International Institute for Population Sciences in Mumbai had written in The Lancet advocating “a random sample-based population surveillance framework”.
Earlier this week, the Indian Council of Medical Research (ICMR), the apex body leading the fight against Covid-19, announced population-based sero-surveys — antibody surveys to understand the prevalence of Covid-19 in the population.
In an email interview with ThePrint, S.V. Subramanian lauded the government and the ICMR for the decision. “At the outset, this is absolutely the right direction for the government of India, led by ICMR, to take in its effort to understand and come up with the right containment and mitigation strategy for COVID-19,” he said.
The professor of population health and geography also urged the research body not to “reinvent a new sampling frame” but utilise the National Family Health Survey 2018-19 (NFHS-5) district-level sampling frame.
NFHS survey for Covid-19 surveillance
The National Family Health Survey (NFHS) is a “large-scale, multi-round survey conducted in a representative sample of households throughout India”. The survey provides pivotal information regarding fertility, infant and child mortality, the practice of family planning, maternal and child health, reproductive health, nutrition, anaemia, utilisation and quality of health and family planning services.
According to Subramanian, the NFHS survey, based on random sampling, yields more accurate results for understanding disease prevalence in a population than the selective testing of at-risk individuals, which is a Covid-19 patient’s contacts.
“In 2002, India was projected to have 25 million HIV-positive individuals, with a prevalence of HIV in adults of 3–4 per cent. These estimates were based on extrapolation of infection rates among selected at-risk individuals,” he said. “India used the NFHS to test for HIV in the general population, and estimates were drastically reduced to 2.5 million, with a prevalence of HIV in adults (aged 15–49 years) of 0.28 per cent. This discrepancy shows the shortcomings of selective testing of at-risk individuals as the basis for understanding disease prevalence in a population.”
In his correspondence to The Lancet, Subramanian had noted that the number of individuals being tested would be different based on three different scenarios. If the disease prevalence was at 0.5 per cent of the population, a sample of 3000 individuals should be tested. The sample size would increase to 15,000 if the prevalence was at 0.1 per cent of the population and would decrease to about 1500 if the prevalence was at 1 per cent.
The ICMR’s community-based survey, which will take place in 69 districts across 21 states, will cover 24,000 adults “distributed equally across four strata of districts categorized on the basis of reported cases of Covid-19”.
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Living with the virus
When asked if the government’s lockdown strategy worked, Subramanian said that it had been implemented with the assumption that “the virus was behind us”.
“But that was simply an assumption. The honest answer is that we did not know where we stood regarding how widespread Covid-19 was. Yet it was clear that some action was necessary,” he said.
“What appears to have been missed is that not much thought was given to when and how the lockdown would be lifted. If containment was complete, then everything would have worked fine,” he added. “However, now that it is clear that the containment strategy was insufficient, we need to begin to think about how to live in tandem with the virus.”
A crucial aspect of this, he explained, would be the preparation of the health infrastructure and behavioral changes.
“India’s biggest advantage is its relatively young population. At the same time, due to the sheer population size, even lower prevalence translates to large absolute numbers. Also, overall public hygiene is an issue that cannot be ignored. In short, while thus far India seems to have handled the crisis well, there should not be any room for any complacency,” Subramanian warned.
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