Representative photo: Kuan Liao/Unsplash.
After peaking at close to 98,000 around September 17, the number of daily new COVID-19 cases in India has steadily declined. If we were to simply extrapolate using this decrease, estimating it to be around 1,300 fewer cases each day, our calculation would suggest that no new cases should be reported in about 75 days from now.
Are we then nearing the end of the Indian COVID-19 epidemic?
What does “end” even mean? Vaccinating around 60% of the population of a country would be sufficient to shield those still unvaccinated. (The exact fraction to be targeted, the ‘herd immunity threshold’, is currently unknown, so this is only a reasonable estimate.) This would serve to halt the further spread of the disease. However, we have no vaccine – yet – against COVID-19.
Apart from that, if you happen to be a small island country that catches the pandemic early enough and can efficiently identify new cases, you stand the best chance of cutting it off well before it sweeps through your population. Both Taiwan and New Zealand are success stories for these reasons. Another alternative is to rigorously test, trace and isolate – i.e. the South Korean model. Whether the success of these countries will be a lasting one will ultimately depend on how well they can continue to screen those who enter, given that almost all of their population will remain susceptible to the disease.
The scenario that should apply to much of the world currently is the following: As the pandemic in a country proceeds, and more and more people fall ill and recover (or die), it becomes increasingly harder to find someone who has never been infected before. In general, epidemics wind down once a typical infected person cannot find someone susceptible whom they can infect before they themselves recover.
(If being infected does not guarantee immunity against a second infection, the matter becomes more complicated. Reinfections with COVID-19 do happen, although rarely, as far as we know now, and we’ll ignore them for the sake of our argument.)
At the point where disease numbers begin to trend downwards, we might expect that about 30% or so of the population – again a ball-park estimate for the sake of argument – would have been infected. With the further lapse of time, more and more people will be infected, even as the numbers of cases each day decrease and those who are ill recover.
Allowing a suitable fraction of the population to be infected so as to protect others from disease is the idea of ensuring herd immunity by infection. For a country to acquire herd immunity by allowing the infection to run unbridled through its population carries significant costs. These include excess deaths from the disease as well as its long-term consequences in those who survive. Most epidemiologists agree that allowing COVID-19 free rein in the hope of reaching that end-point as soon as possible is not a sensible option. The only real hope, then, is to be able to spread out new cases as far as possible, until we have a vaccine – a policy that has come to be called ‘flattening the curve’.
So what does the decline we’re seeing mean for the future of the COVID-19 epidemic in India? One way to think about this is to reason from the results of a recent seroprevalence survey – the second of two conducted so far by the Indian Council of Medical Research (ICMR). This survey looked for signatures of prior COVID-19 infection in a representative sample of adult individuals from 70 districts across India. The survey concluded in early September; its preliminary results suggest that if one excluded major cities from this count, between 6% and 7% of Indians have been infected thus far on average. This is quite far from any reasonable estimate of a herd immunity threshold.
Surveys that specifically targeted major Indian cities have yielded substantially larger numbers of those who have been infected. Pune’s survey concluded that around 51% of those in the areas surveyed had been infected. Mumbai’s survey estimated an overall seroprevalence of 41%. A more recent survey in Delhi arrived at 28%. Even within states, ICMR’s survey suggested an exposure to COVID-19 of about 38% in Vizianagaram, 29.3% in Krishna and 18% in Nellore districts of Andhra Pradesh. It would seem COVID-19’s spread through India has been extremely inhomogeneous.
Our picture, then, is that of a disease that has largely exhausted its supply of susceptible people in these major Indian cities as well as specific districts, while still spreading into the more remote reaches of the country at a slower, more intermittent, pace.
It’s for this reason that happiness over the decrease may be premature. There still remains a large pool of susceptible people in largely rural parts of India who are at risk of contracting COVID-19.
But there are some positives. Rural India is less dense than urban India. Crowded, poorly ventilated conditions, such as those in the urban factories of Surat and Ahmedabad, where many migrant workers were employed, are fertile grounds for a respiratory virus to spread. Rural India has relatively smaller fractions of people with comorbidities such as diabetes or cardiovascular disease compared to India’s cities. Such comorbidities aggravate the risk of adverse outcomes upon infection and disease.
An extensive recent study in the states of Tamil Nadu and Andhra Pradesh suggests that Indians older than about 60 years are at reduced risk of death compared to those of similar age in the developed west, for reasons we don’t yet understand. All these factors lead us to hope that the impact of COVID-19 on the rural Indian population could be blunted. The relatively low test-positivity rates we have seen in Uttar Pradesh and Bihar, according to health ministry data, against a fairly high volume of testing, should give us cause for hope.
Set against these positives are several major causes for worry. In a few weeks, Durga Puja will begin in Bengal. The festival season in North India is also drawing closer. We are on the verge of the winter months, when fewer people will venture outside, preferring to gather indoors in closed, less-ventilated environments. Once large-volume, long-distance public transport is restored, that will link high-prevalence and low-prevalence regions, allowing infected people to move from the former to the latter, and accelerate COVID-19 spread. Add to this mix a weariness with extended lockdowns and restrictions together with an understandable yearning for a return to a pre-COVID-19 life, and it becomes increasingly hard to guess what might happen.
Another worry has to do with the recording of cases. Anecdotally, testing seems to have faltered in several parts of the country, with a number of states, including Maharashtra and Karnataka, still reporting large test-positivity ratios. Kolkata has not seen the sharp rise in cases that India’s other megacities have. Is there anything to suggest that Kolkata is exceptional among Indian cities? It’s unlikely. Whether case numbers there and in other parts of the country reflect the true situation or whether the official numbers conceal a reservoir of undetected infection remains to be seen.
What can we expect in the coming days?
Here’s one plausible scenario, based on the assumption that the official recorded numbers of cases at least approximately resemble reality. Since the pandemic took off in different parts of India at different times and at different rates, overall India numbers should reflect this patchwork of trajectories taken by the epidemic. In a situation closest to the preferred one, we should see a slow decline in the number of cases, with occasional rises superimposed. If we relax our vigil, we run the risk of these blips becoming more sustained increases, perhaps even building up to a “second wave”. But this will most likely be in parts of the country other than those that have already been intensely affected. Any such second wave will last until it runs out of people to infect in the regions where it has spread, on its own steam.
While the hope of an inexorable march downwards, unto a magical point 75 days away – when COVID-19 will vanish, never to return again – will not be fulfilled, we can take some comfort in the fact that for some parts of the country at least, a surge in cases comparable to the initial peak seems unlikely. We may even anticipate a guarded return to some semblance of normal life, although to a new and not an old normal, where regular testing, mask-wearing and physical-distancing will be the norm.
COVID-19 has changed many aspects of how we live, certainly for the foreseeable future, perhaps forever. But to relax our vigilance now – having reached so far and at such cost – is not an option we should consider.
Gautam I. Menon is a professor of physics and biology at Ashoka University, Sonepat, and at the Institute of Mathematical Sciences, Chennai. The views expressed here are the author’s own.