Study reveals how air travel accelerated the spread of Covid-19

The decrease in the distance between Brazilian cities from the networks created by the air network contributed to accelerating the spread of Covid-19 across the country at the beginning of the pandemic.

The data are from a study developed at the Polytechnic School (Poli) of the University of São Paulo (USP), which demonstrated the connections between 5,569 Brazilian cities and analyzed the impact of networks produced by air transport at the beginning of the pandemic.

The analysis compares the networks created by the road network and the air network and verifies that the planes reduced the distances between cities by 70%, accelerating the spread of the disease. The results were published in the journal Scientific Reports.

For the study, the Brazilian researchers used as a basis the small world model, developed by Duncan Watts and Steven Strogatz and published in an article for the journal Nature, in 1998. The model presents the connections between people as a network in which everyone is separated from each other by a few steps – also called nodes.

The USP scientists considered Brazilian cities as nodes that connect to neighboring cities by land, but also cities with airports and frequent flights between them.

“When you think about a pandemic, it is important to think about contact between people. That’s where the network comes in, because individuals will pass the disease on to the people they are connected to,” explained Giovanna Cavali Silva, who is studying an MBA in data science at the Continuing Education Program at USP’s Polytechnic School, in a statement.

By road, direct connections between cities are reduced and steps are longer to reach cities in other regions. Thus, in cases of disease spread, transmission occurs to neighboring cities. As for airlines, considering connections between cities in different regions, for example, the scope of transmission of the disease is much greater. Following the small world model, the article reduced 27 road knots to 7 air knots.

The researchers used data processing software and used a model adopted for simulating epidemics. Data from the National Civil Aviation Agency (Anac), the Brazilian Institute of Geography and Statistics (IBGE) and the Brasil.io public data repository, which monitored the pandemic numbers in the country, were used.

From there, the experts built a network according to geographic positions, which were divided into cities with international airports, local airports and those without air transport. “The simulations were carried out by cities and not by people, that is, each city had a probability of being infected”, points out Evandro Marcos Saidel Ribeiro, professor of the Polytechnic program.

According to data from state health departments, 99% of Brazilian cities confirmed cases of Covid-19 in the twentieth epidemiological week. When adding the aerial possibilities, the distance between the “nodes” dropped by 70%. “The cities are grouped with those in their surroundings, but when adding an air connection, the groups are not broken and the distance decreases drastically”, points out Ribeiro.

Prevention

According to the researchers, the decrease in distances between cities favors the spread of infectious diseases, such as Covid-19. To avoid new epidemics, it is necessary to turn attention to air transport.

“Right at the beginning of the pandemic, it is already possible to detect outbreaks [de disseminação] of diseases, and they will be the airports. It is an extremely connected network, where infections are beyond epidemiological control”, says Giovanna.

Experts suggest considering drastic public health measures to prevent the spread of viruses, such as reducing the number of flights in most affected cities or even closing airports. For them, monitoring and government intervention in this type of transport are essential to prevent the occurrence of pandemics.

(With information from Julia Custódio, from Jornal da USP)