While the conditions that applied at that stage of the Covid-19 pandemic differ from those of today, the study offers a method that could be adapted as the pandemic evolves. The study estimates that from mid-2020 through early 2021, the probability of getting Covid-19 on an aeroplane surpassed 1 in 1,000 on a full flight lasting two hours at the height of the early pandemic, roughly December 2020 and January 2021.
The overall risk of transmission from June 2020 through February 2021 was about 1 in 2,000, with a mean of 1 in 1,400 and a median of 1 in 2,250. Masks are no longer required for U. domestic passengers; in the study’s time period, airlines were commonly leaving middle seats open, which they are no longer doing; newer Covid-19 variants are more contagious than the virus during the study period. While those factors may increase the current risk, most people have received Covid-19 vaccinations since February 2021, which could lower today’s risk — though the precise impact of those vaccines against new variants is uncertain.
Still, the study does provide a general estimate of air travel safety concerning Covid-19 transmission and a methodology that can be applied to future studies. “The aim is to set out the facts,” says Arnold Barnett, a management professor at MIT and aviation risk expert co-author of a recent paper detailing the study’s results. All told, given about 204 million, domestic airline passengers from June 2020 through February 2021, the researchers estimate that about 100,000 cases of Covid-19 were transmitted on flights during that time.
The paper, “Covid-19 infection risk on U. domestic airlines,” appears online this month in the Health Care Management Science journal. An airline policy change spurred the current study about the transmission of the Covid-19 virus from early in the pandemic — Delta Air Lines started leaving open the middle seats on domestic flights to de-densify its planes, a practice that some other airlines followed for a while. To conduct the study, Barnett and Fleming amalgamated public health statistics about Covid-19 prevalence, data from peer-reviewed studies about Covid-19 contagion mechanisms, data about the spread of viruses on airlines generally and the spread of Covid-19 on international airlines, and some available industry data about seat-occupancy rates on domestic jet flights.
They then estimated transmission risks on domestic airlines through extensive modelling. The researchers used a two-hour flight for their estimates because that is about the average duration of a domestic flight. As their aeroplane settings, the scholars used a Boeing 737 and Airbus A320, workhorse planes in the U. with a single aisle, three seats on either side and typical capacities of about 175 passengers.
Most such planes have high-functioning HEPA air-purification systems, which help reduce the transmission risk of airborne illnesses. Using the prevalence of Covid-19 as a starting point and integrating airborne transmission data, Barnett and Fleming modelled what would likely happen on flights filled with various passenger loads.
Ultimately Barnett and Fleming did find a notable dropoff in transmission risk when planes have fewer people on them — whether having fewer passengers is due to lack of demand or because airlines were leaving middle seats open. While it is true that leaving middle seats open does not eliminate all proximity with all other passengers, it does reduce the extent of proximity with others and thus appears to lower the overall transmission risk. As Barnett readily notes, pandemic circumstances and airline policies keep evolving, meaning that their estimates for the 2020-2021 period in the study may not translate precisely to the summer of 2022.
Despite the availability of vaccines, he believes the reduced amount of masking, the more-crowded flights, and easy transmissibility of current variants all mean that risks could have increased. “If we were to estimate the chances of infection now, it could be considerably higher,” Barnett says. Still, he adds, the approach used in this paper could readily be adapted to updated studies about in-flight transmission risks for Covid-19 or other viruses. “Modeling like that presented here could help in assessing the changed situation, much as the general approach might help in connection with a future pandemic,” Barnett and Fleming write in the paper.
Written by: Matthew Thomas
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