Travel bans slow the spread of Covid-19 only if imposed for the right duration, says a new study

As states impose fresh lockdowns of varying durations and intensity to arrest the second wave of the Covid-19 pandemic, a new study shows that medium-duration travel bans are counterproductive –they trap migrants in cities that are Covid-19 hotspots long enough to expose them to the virus, which they then carry to their home districts.

These findings are based on the study of return migration out of Mumbai between March 2020 and August 2020, covering the first national lockdown and the subsequent “unlock” phases. The study also took into account the epidemiological data on the rise in infections in the home districts of the migrant workers.

The study by the University of Chicago’s Energy Policy Institute, whose pre-print (non-peer-reviewed) version has been published, reached the same conclusion for other developing countries such as Kenya, South Africa, Indonesia, Philippines and China.

The researchers used simulations to project the growth of infections in what they called “rural sinks”, or the home districts, of the migrant workers. These showed that shorter travel bans corresponded to fewer infections. During longer bans, infections fell in source cities, again limiting the spread of the pandemic.

“For intermediate durations, we risk a situation where we force people to stay in a region of rapidly increasing Covid-19 (cases), and then we allow them to leave at a time when many of them are likely to be infected. This is what creates the finding of intermediate bans being potentially counterproductive,” said Anant Sudarshan, a co-author of the study and the executive director (South Asia) of the Energy Policy Institute.

Various states have imposed curbs of different durations and intensity, triggering migrant movements – albeit smaller than last year’s. Maharashtra Chief Minister Uddhav Thackeray announced a “mini lockdown” in the state on April 13.

The initial lockdown was for 15 days and came into effect from 8 pm on April 14. The lockdown shuttered public places, activities and services and only essential services were exempted. The fresh restrictions once again triggered a 2020-like return migration from Mumbai – migrants headed to railway stations before and after the announcement, though in smaller numbers.

A few days later, on April 19, Delhi Chief Minister Arvind Kejriwal announced a six-day lockdown in Delhi. On May 9, the Delhi government extended the lockdown till May 17.

Even before Thackeray had announced fresh restrictions in Mumbai, Bhopal saw many migrants returning from Mumbai and Delhi in buses, fearing that they would get trapped again as during the 2020 lockdown.

Reverse migration

“The Mumbai travel bans yield a natural experiment with a common infection source and three distinct travel resumptions,” the research paper said. Mumbai has one of the biggest migrant populations in the country: around 43% of its population originates from another state or district, as per the 2011 Census data cited by the paper.

Prime Minister Narendra Modi announced a national lockdown on the evening of March 24, 2020, that came into effect from midnight, to limit the spread of Covid-19. Maharashtra, like all states, put a ban on travel by bus, train or flight, trapping millions of migrant workers. Distressed by the loss of jobs and incomes and with no security net, migrant workers began walking home in large numbers.

The travel restrictions were lifted in phases, the research noted, thus providing examples of what different durations of travel bans can do to the pandemic’s spread across India. These three phases represent the short, medium and long term scenarios in the study:

• The duration of March 25, 2020, to May 8, 2020, was considered as a short-term ban. Interstate migrants were allowed to return to their home states from early May. The Maharashtra government used buses, from the first week of May, to transport migrant workers to the state’s borders. The first outbound train for migrants (Shramik Special) left Mumbai on May 8, 2020, for Basti in eastern Uttar Pradesh.
• The period from March 25, 2020, to June 5, 2020, was considered medium-term. Migrants leaving for districts within the Mumbai Metropolitan Region were allowed to return starting June 5, 2020.
• The period from March 25, 2020, to August 20, 2020, was considered as a long-term travel ban. Finally, the state allowed the resumption of inter-district bus services on August 19, 2020.

The Maharashtra government told the Supreme Court in June 2020 that about 12 crore migrant labourers had gone home and more than 5,00,000 had been ferried by state transport buses. In the same hearing, the Central government said that 57.2 lakh migrants had been moved to destinations in Uttar Pradesh, Bihar, Jharkhand, Odisha and Madhya Pradesh by trains.

Estimating ‘ideal’ duration

A study of these different phases of travel relaxation and the caseload in home districts of migrant workers revealed that the infections rose when the bans were of intermediate duration. “The analysis takes into account average levels and trends of coronavirus infections in these districts and then looks for ‘spikes/sudden changes’ around the time the ban is lifted,” Sudarshan said. The challenge for governments is to decide how long is long enough, he said.

“Before restricting travel, governments should ask themselves whether they can realistically prevent movement for very long,” he said. “If the answer is no, then imposing the ban may be equivalent to delaying travel and creating a situation where people leave later while carrying more infections.”

The research applies to countries with a lot of migrant labour, Sudarshan emphasised, adding that it did not imply that lockdowns are not helpful more broadly.

The paper stops short of defining an ideal duration because the theoretical model of disease spread shows that the effect of different durations depends on how the disease is progressing inside the hotspot. “This is exactly why we argue it is dangerous to impose these bans in the first place since it is hard to predict how long a ban is going to be long enough… the key question is, when a little restriction is worse than no restriction, we should be very cautious going down this path.”

Patna-based epidemiologist Tanmay Mahapatra told IndiaSpend that travel bans need to be viewed with an eye on multiple factors, and duration is only one of them. “The findings of the paper are interesting but I would like to add that it has to be interpreted with caution,” he said, adding that other factors that must be considered include “the status of the epidemic during the travel ban, testing and case management, Covid-19 appropriate behaviour at both source and destination and the readiness of local authorities to implement the restrictions”.

As India plans for its third wave of Covid-19 infections, it needs to figure out how best to implement travel bans, said Mahapatra. “This second wave has shocked us so much that simple solutions such as [travel] bans and lockdowns will not help anymore. They have to be part of the overall response along with early identification and case management.”

This article first appeared on IndiaSpend, a data-driven and public-interest journalism non-profit.