Home / Science / Health /  Year-end covid curve could be shaped by past festival lessons

For months, covid-19 blossomed in India despite muted public movement. When it finally began slowing down in September, a tailwind appeared: the festival season. New outbreaks arose as Indians began crowding again. As the year-end holiday season approaches, a similar test is now here.

Every year, December is the busiest month for Indian airports. Some tourism-heavy states such as Himachal Pradesh and Uttarakhand are still in the midst of an outbreak. Which way the covid-19 curve goes will depend on the restraint the country exercises over the coming weeks.

The post-Diwali spike in infections did not last long, but Google mobility trends have enough lessons for Christmas and New Year. Most festival-related outbreaks since August have come within days of an extraordinary rise in public mobility, the data show.

For example, footfalls at retail and recreation places were still 58% of pre-pandemic levels when September ended. By Dussehra week in late October, this had soared to 69%, and further to 76% by Diwali.

Mobility scaled back later, but only after the festivals had ended. By then, it was time to make amends, and some state governments imposed night curfews as fears of a second wave arose.

Mobility rose sharply after September-end, but scaled back after Diwali
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Mobility rose sharply after September-end, but scaled back after Diwali

Much before Diwali, Kerala had emerged as an early victim, as its famous initial recovery saw a tragic reversal after Onam. In the days before the festival, Kerala’s retail and recreation mobility had risen to 53% of pre-pandemic level. Nearly four months later, the state still contributes the most new cases in India.

West Bengal suffered the same in the days after Durga Puja. Maharashtra lost its guard in the run-up to Ganesh Chaturthi in August. Local mobility spiked in both cases, and the coronavirus followed suit soon after. Delhi’s severe third wave around Dussehra was also preceded by some rise in mobility, though pollution and the winter could also have been dominant causes.

Most festival-related covid surges were preceded by extraordinary rise in mobility
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Most festival-related covid surges were preceded by extraordinary rise in mobility

Manindra Agrawal, professor at Indian Institute of Technology, Kanpur, said the festivals led to a surge because of higher probability of infection spread. “This probability doubled in November as people were travelling and meeting each other much more," he said, citing a disease prevalence model developed by him and his colleagues in a committee set up by the Department of Science and Technology.

But the outlook for New Year’s week lies in the answer to why the post-Diwali virus scare was short-lived. Agrawal said the only logical explanation appears to be that most Indians—around 55% to 60%—had already got infected by now and had become immune to the virus. This share varied by state, rising to up to 80% in Assam and Telangana, and over 60% in Bihar, he said, citing his model.

This could partly explain Bihar’s curious case, where crowded election campaigns and the popular Chhath festival were followed by no major spike in infections. However, inadequate testing data make such conclusions hasty while trying to predict the next few weeks. Ramanan Laxminarayan, director of the Center for Disease Dynamics, Economics and Policy, said the exact reason for such trends could not be understood without more data and regular serological surveys.

“Spikes are a consequence of opportunities for transmission, existing immunity in the population and other factors that change from week to week," he said.

Laxminarayan said state governments should release more detailed data on those who are being tested, such as age, gender, and geolocation. “If only one in 50 cases are picked up by testing as seems to be the case, we need far more information on these individual tests," he said. Bihar has one of the lowest testing rates in the country, but even among those who get tested, fewer than 0.5% turn out to be infected—also among the lowest.

Can states prevent such post-festival spikes? K. Sujatha Rao, a former Union health secretary, blamed it partly on the lack of political consensus. “If West Bengal had banned Durga Puja festivities, the BJP would have made it an issue," Rao said. “These are emotive issues. Either you impose a full lockdown, or just take the risk."

But festival-related outbreaks were not just led by local outings. Cross-country travel also spiked in October, and could have been a reason.

Indian domestic airlines together carried 6.4 million passengers in November, shows data from the Directorate General of Civil Aviation. This was 49% of last year’s figure, the narrowest year-on-year deficit during the pandemic. The Delhi airport alone handled over 2 million passengers in October, the latest available airports data show. All these figures could only increase this month.

Europe has experienced this before. Holiday travel resumed with zeal after the first wave had come under control earlier this year. But the consequences were bad: one study, led by Thomas Plümper of Vienna University of Economics, blamed summer holidays for about half of the increase in growth rates in cases in Germany by September. Several European countries have now imposed some form of Christmas curbs to avoid a repeat.

A week before Durga Puja, Prime Minister Narendra Modi had appeared on television to warn of the risks festivals pose. Indians paid for complacency, but luckily, not much. Daily new cases have come down to early-July levels. But sustaining this will be a task if public movement remains lax.

According to Rao, the winter and the pollution may be a bigger problem than Christmas in the days ahead, especially in Delhi. Manindra Agrawal of IIT Kanpur is more positive, courtesy his mathematical model. “Nothing will happen," he said. “We are really very close to herd immunity level. There will be very localized outbreaks, but at the macro level things won’t change."

With the pandemic seemingly waning in India, expert opinion will be divided. And so, the safest way may just be to heed to lessons learnt from the festivals so far.

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