What is the probability of contracting Covid-19 while flying? A study led by scientists at the Massachusetts Institute of Technology offers a calculation of this for the period from June 2020 to February 2021. While the conditions at that stage of the Covid-19 pandemic are different from today, the study offers a method that can be adapted as the pandemic evolves .
Between mid-2020 and early 2021, the chance of contracting Covid-19 on a plane was greater than 1 in 1,000 on a fully-booked two-hour flight at the height of the early pandemic, around December 2020 and January 2021, the study estimated. dropped to about 1 in 6,000 on a half-full two-hour flight, when the pandemic was at its worst, in the summer of 2020. The overall risk of transmission from June 2020 to February 2021 was about 1 in 2,000, an average of 1 in 1,400, and an average of 1 in 2,250.
To be clear, the current setting is different from the study setting. Masks are no longer required for US domestic passengers; during the time period of the study, airlines usually left the middle seats open, which they no longer do; and new variants of Covid-19 are more contagious than the virus during the study period. Although these factors may increase current risk, most people have received Covid-19 vaccinations since February 2021, which may reduce today’s risk, although the exact impact of these vaccines on the new variants is unknown.
However, the study provides a general assessment of the safety of air travel in relation to the transmission of Covid-19 and a methodology that can be applied to future research. Some U.S. carriers said at the time that on-board transmission was “virtually non-existent” and “almost non-existent,” but the study found there was a notable risk. On the other hand, passengers also did not face the possibility of catching the virus during the flight.
“The goal is to lay out the facts,” says Arnold Barnett, a professor of management at MIT and an aviation risk expert who co-authored a recent paper detailing the study’s findings. “Some people might say, ‘Oh, that doesn’t sound good.’ But if we at least tell people what the risk is, they can make up their own mind.”
As Barnett also points out, a round-trip flight with a change of planes and two two-hour legs each way counts as four flights in this calculation, so a 1 in 1,000 chance per flight would translate to about a 1 in 250 chance of such a journey overall.
Overall, considering about 204 million US domestic airline passengers from June 2020 to February 2021, the researchers estimate that about 100,000 cases of Covid-19 were transmitted on flights during that time.
The paper, Risk of COVID-19 on US Domestic Airlines, appears in advance online this month in the journal Health care management science. The authors are Barnett, who is the George Eastman Professor of Management at the MIT Sloan School of Management; and Keith Fleming, a student in the MIT Sloan Master’s Program in Business Analytics.
Barnett is a longtime expert on airline safety who, among other topics, has analyzed the long-term decline in plane crashes over the past decades. The current study on the transmission of the Covid-19 virus was prompted by a change in airline policy since the beginning of the pandemic – Delta Air Lines began leaving the middle seats open on domestic flights to reduce the crowding of its planes, a practice that some other airlines followed for some time. (Delta and all other airlines no longer use this policy.)
To conduct the study, Barnett and Fleming combined public health statistics on the prevalence of Covid-19, data from peer-reviewed studies on the mechanisms of transmission of Covid-19, data on the spread of viruses in airlines in general and the spread of Covid-19 on international airlines, and some available industry data. US domestic seat occupancy data. They then assessed the risk of transmission on US domestic airlines using extensive simulations.
For their estimates, the researchers used a two-hour flight because that’s about the average length of a domestic flight in the United States. three seats on either side and a normal capacity of about 175 passengers. Most of these aircraft have high-performance HEPA air purification systems that help reduce the risk of airborne transmission.
Using the prevalence of Covid-19 in the US as a starting point and combining airborne transmission data, Barnett and Fleming modeled what might happen on flights filled with a wide variety of passengers. The simulation includes a number of adjustments to make the passenger profile as realistic as possible. For example, airline passengers are slightly more affluent than the US population as a whole, and Covid-19 has affected wealthier populations slightly less than other social groups, so these things are quantified in the study among other factors.
After all, Barnett and Fleming did find a marked reduction in the risk of transmission when there were fewer people on planes—whether the fewer passengers were due to a lack of demand or because airlines were leaving the middle seats open. While it is true that leaving the middle seats open does not eliminate complete proximity to all other passengers, it does reduce the degree of proximity to others and thus reduce the overall risk of transmission.
” [medical] the literature suggests that proximity matters,” Barnett says.
As Barnett readily notes, the circumstances of the pandemic and airline policies continue to evolve, which means their estimates for 2020-2021. the study may not include the summer of 2022. Even with the availability of vaccines, he believes that reduced masking, more crowded flights and the easy transmission of current variants all mean that the risks may have increased.
“If we were to estimate the probability of infection now, it could be much higher,” Barnett says.
However, he adds, the approach used in this paper could easily be adapted to updated research on the risks of in-flight transmission of Covid-19 or other viruses.
“Modeling like the one presented here can help assess the changing situation, just as a general approach can help with future pandemics,” Barnett and Fleming write in the paper.
MIT Libraries provided open access funding, making the paper free for readers.