Airline Passengers Found ‘Very Safe’ From COVID-19

Air passenger contact tracing is unlikely to be necessary for aerosol transmission
inside an airliner showing seats

The COVID-19 pandemic has led to questions regarding the potential risk of SARS-CoV-2 exposure amongst passengers on an aircraft, and the safety of travelers. 

‘It is difficult to determine the potential exposure risk using available computational fluid dynamics models or contact tracing methods, due to the lack of experimental validation of aerosol transport in the aircraft environment and the lack of detailed tracking of human interactions in aircraft,’ stated researchers in a new United States Transportation Command, The Defense Advanced Research Project Agency, and Air Mobility Command sponsored testing.

Published on October 15, 2020, these researchers used fluorescent aerosol tracers between 1-3 µm and real-time optical sensors, coupled with DNA-tagged tracers to measure aerosol deposition, these researchers completed the largest aircraft aerosol experimental validation testing to date, with 8 days of testing involving both inflight and ground tests on Boeing 777-200 and 767-300 airframes. 

Tracer aerosols were released from a simulated infected passenger, in multiple rows and seats, to determine their risk of exposure and penetration into breathing zones of nearby seats. 

In particular, penetration into the breathing zones of passengers seated in the same row and in numerous rows in front and back of the source were measured. 

Over 300 aerosol release tests were performed repeatedly releasing 180,000,000 fluorescent tracer particles from the aerosol source, with 40+ Instantaneous Biological Analyzer and Collector (IBAC) sensors placed in passenger breathing zones for real-time measurement of simulated virus particle penetration. 

In total, more than 11,500 breathing zone seat measurements were taken with releases in 46 seats of the airframes. 

Results from the Boeing 777-200 and 767-300 airframes showed a minimum reduction of 99.7% of 1 µm simulated virus aerosol from the index source to passengers seated directly next to the source. 

An average 99.99% reduction was measured for the 40+ breathing zones tested in each section of both airframes. 

Rapid dilution, mixing, and purging of aerosol from the index source was observed due to both airframes’ high air exchange rates, downward ventilation design, and HEPA-filtered recirculation. 

Contamination of surfaces from aerosol sources was minimal, and DNA-tagged 3 µm tracers agreed well with real-time fluorescent results. 

Transmission model calculations using the measured aerosol breathing zone penetration data indicates an extremely unlikely aerosol exposure risk for a 12-hour flight when using a 4,000 virion/hour shedding rate and 1,000 virion infectious dose.

However, the contamination of surfaces via non-aerosol routes (large droplets or fecal contamination) is more likely in lavatories and other common areas and were not tested in this study.

Given the data captured during this most recent round of testing, and coupled with existing literature and a growing consensus on COVID-19 risks, the following recommendations regarding troop transport on commercial airlines can be conveyed:

  • Aerosol exposure risk is minimal even during long-duration flights, but typically highest in the row of an index patient. Rows in front and behind the index patient have the next highest risk on average.
  • While there is a measurable difference in the middle vs aisle or window seat, there is no practical difference at these high overall reduction levels.
  • The benefit of commercial airframes and the validity of these recommendations rely on the combination of a HEPA-filtration recirculation system and the high air-exchange rate, which is not matched by other indoor venues, including most hospital and biosafety-level 3 laboratories.
  • Overhead gasper supply (on or off) does not make a significant impact on aerosol risk and could continue to be used primarily for traveler comfort.
  • Flight deck exposure risk is extremely unlikely, as the ECS system supplies separate air to this portion of the aircraft.
  • Keeping air supply and recirculation mode (HEPA-Filtration) operating is critical. Ground supply and APU behave similarly, but there is likely more uncertainty with variations in ground supply flow rates and suppliers since the test team was only able to test the single provided system.
  • Jetway exposure risk from an infected person already sitting in the airframe was low with reductions for the 777 and 767 terminal of 99.999%.

Furthermore, contact tracing should be limited and is unlikely to be necessary for aerosol transmission.

But, contact tracing may be necessary for large droplet transmission in the seats immediately neighboring an infectious passenger, or from uncertainty in human behavior.

United Airlines, which donated flight time for this study, stated the new research as “landmark.”

“Your chances of COVID exposure on a United aircraft are nearly non-existent, even if your flight is full,” Toby Enqvist, United Airlines’ chief customer officer, reported Reuters.

Vax-Before-Travel publishes research-based travel news.