Looming Third Wave: A nagging fear of a third COVID wave looms over India. Although none of us wants a fresh Covid wave in our country, there are worrying signs that warns us about a possible third wave. For the past few days, Kerala has been logging over 30,000 daily cases; other regions such as Mumbai and Delhi have also witnessed a slight rise in daily cases (News18, Aug. 28, 2021).

One intriguing thing is that the state reporting the highest surge is also the one with the highest level of full vaccinations.

We must realise that a fresh COVID wave would be the result of a complex interplay of factors: the level of susceptible population, adherence to Covid-appropriate behaviour (CAB), the pace of vaccinations, and adequate testing, tracing, treatment and healthcare facilities. This interplay may be further confounded by the rise of new variants, if any. Kerala has fully vaccinated nearly 27 per cent of its population (with two vaccine doses) but its seroprevalence is only 44 per cent (that is, nearly 60 per cent of Kerala's population is still susceptible to the virus). On the other hand, the average national seroprevalence is about 67 per cent (that is, about 33 per cent Indians are still vulnerable to COVID-19 on average) but the average fully vaccinated Indian population is just 15 per cent.

The reasons for the surge in Kerala isn't known with certainty but many experts ascribe it to violations of COVID restrictions in the recent Bakrid and Onam celebrations. One mitigating factor is that there has not been corresponding rise in hospitalisations and deaths in Kerala, possibly hinting at adequate healthcare infrastructure in the state. However, the rapid rise in infections, despite high level of vaccinations, point towards inappropriate tracing and isolation protocols. The virus does not recognise any VIP; for it, every susceptible individual is a VIP, allowing it to reproduce and infect as many hosts as possible. So the take-home lesson is that, crowding must be avoided meticulously irrespective of whether the gathering is religious, cultural, political, or academic. Both the central and state governments must enforce adequate testing, tracing, isolation, and treatment protocols to prepare for a possible third COVID wave. And, there is urgent need to scale up the healthcare infrastructure including pediatric facilities, as there are reports that claim that children would be hit hard in the third wave (please note that there are also equally  assertive reports claiming the contrary). As vaccines prevent hospitalisations and deaths to a great extent (though they may not prevent infections altogether), we must ramp up vaccinations so that over 50 per cent of the eligible population gets fully vaccinated (that is, they receive two vaccine doses) in the next two-three months. This is critically important as there are many reports now which show that 1 dose has very low effectiveness against the delta variant.

There are now several contrasting reports about the third wave, differing in the timing and severity. Some warn about the impending third wave which would be quite severe. Others say that the third wave would come much later and it would be much more milder than the second wave. We may, however, err on the side of caution, and start adequate preparations, assuming that a fresh Covid wave is going to strike us soon. Let's now look at some recent models about the looming third wave in India.

Dr Jayaprakash Muliyil, epidemiologist, rules out the possibility of any significant third wave in India. But Dr Gautam Menon, Ashoka University, says that the third wave could be a "steady hill" instead of the "steep mountain" of the second wave (with steep rise and decline in cases). Whether the steady hill would turn into a full-blown wave; we've to wait and see. Several factors will determine the trajectory of the third wave, the protection from prior infections or vaccinations, rise of vaccine-resistant variants, the effectiveness of current vaccines, CAB, adequate/inadequate test, trace, isolate, treat protocols and healthcare infrastructure etc.

Profs. Ranjan and Verma, IIT Kanpur, in an earlier model, considered three scenarios. If life goes back to normal, India would see a third wave peak by October, milder than the second wave (Scenario 1). If life goes to normal and a new variant arises, there will be a peak by mid-September, which could be more severe than the second wave (Scenario 2). If stricter restrictions continue in India, the third wave would peak in late October and it would be much more milder than the second wave (Scenario 3).

Another model by Profs. Vidyasagar and Aggarwal, IIT, predicted that a third wave would peak in October 2021 and the upward curve could be seen in August. In the best-case scenario, India would see 1 lakh infections per day, while there could be 1.5 lakh new daily infections in the worst-case scenario (The News Minute, Aug. 20, 2021).

Indian Institute of Science (IISc), Bangalore, scientists led by Prof S Ganesan predicted that, if a new variant emerges, Karnataka could see 20 lakh cases between August 22 and September 10, 2021. The key findings of the study are: new variants and crowding would be main reasons for the 3rd wave; increase in vaccination rate would reduce active caseloads, hospitalisations, and deaths; vaccination pace must be doubled to reduce possibility/severity of 3rd wave; and impact of 3rd wave on children (Age 0-18) could be 13 times higher than that in 2nd wave (New Indian Express, Aug. 9, 2021).

According to a US model, India would see a 'small bump' in August, but the peak of the third wave would come in November 2021 (The Print, Aug. 3, 2021). This was a modeling study done by Dr Bhramar Mukherjee, Michigan University. She predicted that "infections are likely to be rising again with a small bump...the more prominent third wave peak appears to be on the horizon sometime around November."

However, it must be noted that, even without the emergence of new variants, the delta strain which is as contagious as chickenpox and can be passed on by vaccinated people, can still trigger the third wave, if we ignore CAB, do not scale up vaccinations (two doses), and don't enforce appropriate test-trace-isolation-treatment procedures.

A worrying development is that Karnataka has recently seen a rise in Covid cases among children (India.com; Aug. 19, 2021; last accessed, Aug. 28, 2021). 543 children were found to be Covid-positive in the state in the first 10 days of August.

New variants