Travel surges before lockdown undermine the SARS-CoV-2 containment effort

Nations around the world have enacted unprecedented travel restrictions and lockdowns in response to the coronavirus disease 2019 (COVID-19) pandemic. These measures ranged from movement restrictions on a local level to regional and international travel restrictions.

These restrictions are put in place to contain the spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus through minimizing contact between potentially infectious people and individuals susceptible to infection. They also help slow down the spread of the disease from epidemic hotspots to other places, thus preventing the overloading of healthcare systems. However, ultimately, the public's response to these announcements of restrictions on both local and long-distance travel determines how effective these non-pharmaceutical interventions are.

Governments should warn the public about upcoming restrictions on travel so they can make necessary preparations. Still, then a travel surge right before the lockdown starts could cause the exact opposite of the desired effect. Travel surges could send potentially infectious people from the hotspots to other regions previously unaffected by the pandemic. Understanding how people respond to such interventions is critical to design effective lockdown policies to contain SARS-CoV-2 transmission or even in the context of future pandemics.

Percent change in weekday nighttime population of Facebook users by city. We can see that all cities included in the Facebook sample experience a decrease in nighttime population over the period of interest.
Percent change in weekday nighttime population of Facebook users by city. We can see that all cities included in the Facebook sample experience a decrease in nighttime population over the period of interest.

Measuring the impact of announcement of restrictions on human mobility patterns

Recently, researchers from the Harvard T.H. Chan School of Public Health, Boston; the University of Illinois at Urbana Champaign; and the University of California, USA, assessed the impact of the announcement and implementation of restrictions such as lockdowns on mobility patterns of humans. Their work is published on the preprint server medRxiv*.

The researchers analyzed aggregated mobility data extracted from mobile phones to see how lockdown announcements and implementation affects human mobility. Using a simple agent-based spatial model, they examined how human behavioral responses to lockdown announcements could contribute to the epidemic's spread.

Sudden lockdown announcements lead to local, regional, and international travel surges

This study's findings show that at an individual level, factors such as the local contact rate, delay between announcement and implementation of lockdown, or travel outside urban centers do not affect the risk of epidemic propagation much. However, the researchers warn that the multiplied effects of all these factors combined can be very drastic.

The team found that there was an increase in local and long-distance movement following the lockdown announcement. Their analysis showed that increased mobility following lockdown announcements could boost epidemic seeding in rural areas, which undermines the lockdown's purpose, preventing the spread of disease.

"While many factors likely contributed to the similarities in the epidemic curves across locations, the increase in travel in the mobility data suggests seeding from urban areas may have played a role."

Successful lockdowns are the key to containing the spread of disease to rural areas

Globally, there are longstanding disparities between urban and rural areas with respect to healthcare access, and the SARS-CoV-2 pandemic has further exacerbated them. Lockdowns that effectively minimize contact and travel can be a crucial tool for containing the spread of disease into rural areas. However, the initial travel surges following the announcement of lockdowns can catalyze the epidemic's spread to rural areas that may not be well equipped to handle an epidemic.

"Mobility and epidemiologic data support the findings from our model of increased exportation and seeding of epidemics as a result of travel surges."

Thus, surges in travel increase the need for surveillance, testing, and treatment in rural areas that may be understaffed and underequipped. The simulation used in this study shows that, through the course of a partially contained epidemic in a susceptible population, rural areas will still be impacted, though at a later date.

The authors believe that putting out appropriate messaging along with lockdown announcements and implementing measures to bring down unnecessary travel are crucial for preventing such unintended consequences of restrictions such as lockdowns.

"Appropriate messaging to decrease the spike in local contact rates and exodus out of epidemic areas along with inter-region coordination of movement can help decrease the burden of disease experienced by rural areas."

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Susha Cheriyedath

Written by

Susha Cheriyedath

Susha has a Bachelor of Science (B.Sc.) degree in Chemistry and Master of Science (M.Sc) degree in Biochemistry from the University of Calicut, India. She always had a keen interest in medical and health science. As part of her masters degree, she specialized in Biochemistry, with an emphasis on Microbiology, Physiology, Biotechnology, and Nutrition. In her spare time, she loves to cook up a storm in the kitchen with her super-messy baking experiments.

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