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CDC Study Shows Benefits in Blocking Middle Seats

The Centers for Disease Control and Prevention (CDC) has issued a report on the laboratory findings on COVID-19 exposure on board aircraft, just as daily flight movements show a sustained upturn.

Based on laboratory modeling of exposure to SARS-CoV-2 on single-aisle and twin-aisle aircraft, exposures in scenarios in which the middle seat was vacant were reduced by 23% to 57%, compared with full aircraft occupancy, depending upon the model.

The study by CDC and Kansas State University found that a 23% exposure reduction was observed for a single passenger who was in the same row and two seats away from the SARS-COV-2 source, rather than in an adjacent middle seat. When quantifying exposure reduction to a full 120-passenger cabin rather than to a single person, exposure reductions ranging from 35.0% to 39.4% were predicted. A 57% exposure reduction was observed under the vacant middle seat condition in a scenario involving a three-row section that contained a mix of SARS-CoV-2 sources and other passengers. 

Based on this laboratory model, CDC determined that a vacant middle seat reduces risk for exposure to SARS-CoV-2 from nearby passengers. 

The study addresses only exposure and not transmission and CDC notes in its report that the impact of masks was not considered in the aerosol analysis because masks are more effective at reducing fomite and droplet exposures than aerosol exposures. CDC points to a case study of COVID-19 transmission on a flight with mandated mask wearing that suggests that some virus aerosol is emitted from an infectious masked passenger, indicating that distancing could still be useful. 

CDC noted four limitations to the study, including that data were collected under higher relative humidity conditions in the laboratory than would be present during a commercial flight.

The International Air Transport Association (IATA) was critical of the report for not taking into account mask wearing. IATA underscored that there have not been large numbers of confirmed or suspected cases of onboard transmission reported at any stage of the pandemic, and almost all of those that were, occurred without the wearing of masks on-board. 

The association highlighted a report by the U.S. Transportation Command, which found that the overall exposure risk from aerosolized pathogens, like coronavirus, is “very low” on the types of airline aircraft typically contracted to move Department of Defense (DOD) personnel and their families. In the study, more than 300 aerosol releases, simulating a passenger infected with COVID-19, were performed over eight days using United Airlines Boeing 767-300 and 777-200 twin aisle aircraft.

IATA also quoted the Harvard School of Public Health Aviation Public Health Initiative in its Phase 1 Report on the risks of COVID-19 transmission during air travel in which it stated: “This research substantiates that the layered approach of Non-Pharmaceutical Interventions (NPI) instituted on commercial aircraft – effectively diluting and removing pathogens and in combination with face masks – results in a very low risk of SARS-COV-2 disease transmission on aircraft.”

Most airlines are now filling middle seats. Delta is reported to be the last major U.S. airline to block middle seats but is expected to stop doing so from May 1.

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Kylie Bielby
Kylie Bielby has more than 20 years' experience in reporting and editing a wide range of security topics, covering geopolitical and policy analysis to international and country-specific trends and events. Before joining GTSC's Homeland Security Today staff, she was an editor and contributor for Jane's, and a columnist and managing editor for security and counter-terror publications.

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