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JAMA Patient Page
October 1, 2020

Risk of COVID-19 During Air Travel

Author Affiliations
  • 1Aerospace Medical Association, Alexandria, Virginia
  • 2International Airline Medical Association, Alexandria, Virginia
  • 3International Air Transport Association (IATA), Geneva, Switzerland
JAMA. Published online October 1, 2020. doi:10.1001/jama.2020.19108

The risk of contracting coronavirus disease 2019 (COVID-19) during air travel is lower than from an office building, classroom, supermarket, or commuter train.

How Is COVID-19 Transmitted?

The virus that causes COVID-19 is emitted when someone talks, coughs, sneezes, or sings, mainly in droplets that can be propelled a short distance, and sometimes in smaller aerosol particles that can remain suspended and travel further. Another person can be infected if these particles reach their mouth or nose, directly or via hands. Transmission via surface contact is also important in some cases.

How Clean Is the Air in Passenger Aircraft?

Air enters the cabin from overhead inlets and flows downwards toward floor-level outlets. Air enters and leaves the cabin at the same seat row or nearby rows. There is relatively little airflow forward and backward between rows, making it less likely to spread respiratory particles between rows.

The airflow in current jet airliners is much faster than normal indoor buildings. Half of it is fresh air from outside, the other half is recycled through HEPA filters of the same type used in operating rooms. Any remaining risk to be managed is from contact with other passengers who might be infectious. Seat backs provide a partial physical barrier, and most people remain relatively still, with little face-to-face contact.

Despite substantial numbers of travelers, the number of suspected and confirmed cases of in-flight COVID-19 transmission between passengers around the world appears small (approximately 42 in total). In comparison, a study of COVID-19 transmission aboard high-speed trains in China among contacts of more than 2300 known cases showed an overall rate of 0.3% among all passengers. Onboard risk can be further reduced with face coverings, as in other settings where physical distancing cannot be maintained.

Risk Reduction Steps by Airports and Airlines

Steps being taken at airports and on board can include temperature testing and/or asking about symptoms (fever, loss of sense of smell, chills, cough, shortness of breath); enhanced cleaning and disinfection; contactless boarding/baggage processing; use of physical barriers and sanitization in airports; physical distancing in airports and during boarding; use of face coverings or masks; separation between passengers on board when feasible; adjustment of food and beverage service to reduce contact; control of access to aisles and bathrooms to minimize contact; limiting exposure of crew members to infection; and facilitation of contact tracing in the event that a passenger develops infection.

Additional steps being studied are preflight testing for COVID-19 and adjustments to quarantine requirements.

Steps Passengers Can Take

Wear a mask, don’t travel if you feel unwell, and limit carry-on baggage. Keep distance from others wherever possible; report to staff if someone is clearly unwell. If there is an overhead air nozzle, adjust it to point straight at your head and keep it on full. Stay seated if possible, and follow crew instructions. Wash or sanitize hands frequently and avoid touching your face.

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Article Information

Published Online: October 1, 2020. doi:10.1001/jama.2020.19108

Conflict of Interest Disclosures: Dr Pombal reported being an employee of TAP Air Portugal Group Health Services and is chairperson of the Aerospace Medical Association Air Transport Medicine Committee. Dr Hosegood reported being an employee of Qantas Airways and is president of the International Airline Medical Association. Dr Powell reports receipt of personal fees from the IATA.

Sources: Centers for Disease Control and Prevention, World Health Organization, IATA, European Centre for Disease Prevention and Control

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    13 Comments for this article
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    Australian Experience
    Brian Cox, MBChB, PhD, FAFPHM | University of Otago
    This article appears to contradict a widely reported instance of a 'superspreader' event during air travel:

    www.smh.com.au/national/ruby-princess-passengers-on-qantas-flight-infected-at-least-eight-others-20200930-p560no.html
    CONFLICT OF INTEREST: None Reported
    When Passengers Remove Masks Flying Remains a Risk
    Peter Schnall, Professor of Medicine | U of California at Irvine
    Airlines continue to make progress in improving the safety of passengers from contacting and contracting Covid-19. The filtered air in the planes is not the issue IF the planes have newer HEPA filters (not all do).

    Unfortunately, the main safety problem is that on an airline passengers remain in close proximity to each other (often within 2 feet) and they are NOT necessarily required to remain masked during the entire flight. Airlines in fact encourage mask removal by providing food and beverages during most flights of greater than 1-2 hours duration. Some passengers take advantage of this
    by removing masks during flights after purchasing food and beverages and then extending the time they eat and drink (and keep their masks off). Anyone sitting within 6-10 feet of someone infected and not wearing a mask is at risk for infection.

    It cannot be stressed enough that flying is risky during an epidemic and the most important safety measure is mask wearing (an N95) during the entire flight as well as in the airport (preferably also wearing a face shield as well to reduce the likelihood of virus falling on one's face and mask).
    CONFLICT OF INTEREST: None Reported
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    COVID-19 Transmission has Occurred on Aircraft
    Wayne Maksylewich, MSc, MEng | Retired ventilation engineer, Certified Industrial Hygienist (CIH)
    As a ventilation engineer with 40+ years experience in exposure control (including biohazard labs) I find the assertion that general ventilation on an aircraft - as opposed to local exhaust - will effectively control close quarter exposure to "droplets" (or, more technically correct, an aerosol from coughing, sneezing or talking) is questionable. See Lydia Bourouiba, JAMA March 26, 2020 for a photo of what occurs when sneezing or coughing, and the following references for reports of aircraft spread (1-3).

    References

    1. Nguyen Cong Khanh et al. Transmission of Severe Acute Respiratory Syndrome Coronavirus 2 During Long Flight. Emerging Infectious
    Diseases Volume 26, Number 11—November 2020 

    2. Hollie Speake et al. Flight-Associated Transmission of Severe Acute Respiratory Syndrome Coronavirus 2
    Emerging Infectious Diseases Volume 26, Number 12—December 2020 

    3. Edward M. Choi et al. In-Flight Transmission of Severe Acute Respiratory Syndrome Coronavirus 2 
    Emerging Infectious Diseases Volume 26, Number 11—November 2020
    CONFLICT OF INTEREST: None Reported
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    Air Recirculation and Spread of Virus
    Quang Pham, PhD (Chem. Eng.) | Retired lecturer in engineering
    Unfortunately, airflow is never as ideal as the Figure suggests. Surrounding air gets entrained into the jet and disturbed by it, causing complex circulation patterns that can carry the virus to other passengers a fair distance from the source. See the following simulation by Purdue University researchers: https://twitter.com/Droit_IA/status/1255581175399227395 and the paper at https://engineering.purdue.edu/~yanchen/paper/2011-2.pdf.
    CONFLICT OF INTEREST: None Reported
    Don't Abdicate Personal Safety to Airplane Measures
    Shyan Goh, MBBS FRACS | Private
    While it is true that air circulation in plane cabins are often better than other public transport and office buildings, and many airplanes made since 1990s have HEPA filters, it is important to know the following:

    1. Many US national airlines still have some McDonnell Douglas airframes in their line up, which are on average 25+ years old; regional airlines may fly even older airplanes
    2. Modern but smaller airplanes may still not carry HEPA air filters
    3. HEPA air filters are often placed in the forward cargo and middle of the passenger cabin; I am not able to
    verify if this significantly impact air circulation in the aft compartment
    4. While most diagrams featuring HEPA filter efficacy involves nice arrows of air circulation, it does not portray turbulent or stagnant air flow which often occur when obstructing objects are present, namely passengers, hand baggage on the floor or seat air vents/nozzles are open.
    5. HEPA filters are not always turned on when planes are stationary, particularly during boarding

    Of interest as well, HEPA filters in hospital operating theatres maintain positive air pressure by ensuring filtered air inflow, whereas isolation room for infective COVID-10 patients with negative pressure environment often only involve HEPA filters only when safe external air exhaust is not possible thus requiring air recirculation.

    And of course no amount of filtered air can adequately mitigate the exponentially increased risk of transmission when you are sitting right next to an infectious individual.

    Short of not flying, passengers cannot always control what and how the plane is running, where they sit or who is sitting next to them. Personal protection and hygiene is still the key to risk minimisation, of which suitable disposable (at least) 3-layered mask and personal area cleaning are generally the keystones to adequate barrier to infection transmission

    I guess no one in 2020 is now laughing at pre-flight cleaning routine videos uploaded in 2019 by various celebrities.
    CONFLICT OF INTEREST: None Reported
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    HEPA Filters
    Bruce Davidson, MD, MPH | Providence Health System, Seattle WA
    Pilots have told me they see that HEPA filters on the larger (e.g., 737) Boeing aircraft are poorly seated, so unfiltered air in the stream passes by without being filtered; also that filters are charged with material and turn black before being changed in some instances. HEPA filters are best used behind standard inexpensive filters with bigger holes, that remove the dust and innocuous material that would otherwise soon "over-charge" the HEPA filter. But I'm told by an airline's Vice-President for safety that there is no room to install such a pre-filter on Boeing aircraft.
    CONFLICT OF INTEREST: None Reported
    HEPA filters
    Bill Kinsey, PhD | Leiden University
    So much of what is written assumes there is a universal quality standard for HEPA filters. There is not. Go online and search for HEPA, and you'll find the many different variants. Back in the old days of the Boeing 707 and their ilk, the filters used were of a higher standard than the TB wards in hospitals. But these were too expensive, and the airlines pushed for cheaper--and less effective--filters. And these are what the airlines are using today. And, as a previous comment noted, the frequency of filter changes is often not what it should be.
    CONFLICT OF INTEREST: None Reported
    Not the Whole Story
    Philip Johnson, MB.BS MFOM DAvMed | Sarum Occupational Health
    “Risk” in this scenario is not the risk of a single activity, but the whole process. Just the activity of leaping out of an aircraft wearing a wing suit (just the leaping out) is safe - the rest of it (flying and landing it) has an established risk profile.

    We are told that “ The risk of contracting coronavirus disease 2019 (COVID-19) during air travel is lower than from an office building, classroom, supermarket, or commuter train.” However that fails to put the issue into any context. Where flight is essential, a process of risk mitigation may
    be relevant. That would surely include “PPE” (with a protection factor) and not “face rags” which have, though governments insist otherwise, no proven protective relevance. To compare air travel with education, shopping for food, or earning a salary is to miss the point completely.

    For most people, air travel is far from essential. We must compare accurately and reasonably if we hope to inform.
    CONFLICT OF INTEREST: None Reported
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    No Context for Claims
    Stefan Gingerich, MS | Minnesota Department of Health
    The first line of this piece states "The risk of contracting coronavirus disease 2019 (COVID-19) during air travel is lower than from an office building, classroom, supermarket, or commuter train." What follows is a reasonable defense of the infection prevention practices taken by some airlines, but it's completely without context. The authors seem to be trying to give readers the reassurance that if they visit an office building, classroom, supermarket, or commuter train, they should also be perfectly comfortable traveling in an airplane. What they fail to do, however, is demonstrate a quantitative risk of any of these activities. If, for instance, I visit a 10,000 square-foot supermarket that has 50 employees and 50 customers at the moment I visit, social distancing is very, very easy and my risk of contracting SARS-CoV-2 is virtually zero. Clearly, not every supermarket (or airplane) is the same, but some attempt at quantify the risk of each activity mentioned would help make their point much more effectively, though I would still rather visit a supermarket than travel in an airplane, for a variety of reasons.
    CONFLICT OF INTEREST: None Reported
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    Author Response - Low Risk of Transmission
    David Powell, MBChB FAFOEM DAvMed | Medical Advisor, IATA
    Thanks for the various comments on HEPA filter performance/maintenance, and on the cases of reported in-flight spread which we knew well. We reviewed the published instances of possible/probable in-flight spread including Khanh et al, and Speake at al, as quoted by commenters. The total suspected secondary cases in the reported literature (excluding 3 pre-prints with insufficient information to evaluate) for 2020 is 42; this number includes a few cases which arose from our own enquiries directly with airline medical departments of a large proportion of the world's airlines. About half of the total number is from two flights reported in the papers mentioned above, from London-Hanoi and within Australia.

    This total number is likely to be an underestimate, but even if there are 10 times this number or more, the total is extremely low when viewed against a total of 1.2 billion airline passengers carried in 2020. The vast majority of these cases occurred in February-March before wearing of face coverings was common practice on board. Since this became the norm (albeit with reduced passenger numbers), there have been almost no reports of suspected cases.

    Thanks also for the comment regarding airflow. From extensive review of published work (including the FAA ACER study series) on airflow in the cabin, and unpublished ongoing work by aircraft manufacturers, we understand that there can be a degree of crosswise flow within the cabin, and some longitudinal flow extending a couple of rows, as reflected in those cases where transmission has been observed. However, the cabin air system was designed specifically to minimise cross-infection risk, and we would submit that the low number of cases appears to indicate this is indeed being achieved.

    We also stress that all efforts need to be continued to manage the risks for travelers. Commenters have pointed to possible lapses with mask wearing or filter maintenance but the procedures, created under the ICAO "Take-off guidance" after extensive consideration of those process, appear to be successful in mitigating the inevitable risk that comes with travel. HEPA filter installation and replacement cycles are laid down by manufacturers and we believe them to be consistently applied, also noting they are present on all current-generation Western jet airliners.

    Our assessment of the medical factors is available at: https://www.iata.org/contentassets/f1163430bba94512a583eb6d6b24aa56/covid-medical-evidence-for-strategies-200806.pdf

    The next update is due shortly to incorporate the latest case reports.
    CONFLICT OF INTEREST: Receive fees for giving medical advice to IATA
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    Article with Numerical Risk Assessment
    John Sanders, DVM |
    In reading the letter above, I don't see any number quantifying risk. I have found a preprint article that has worked out the point estimates that may help a person decide if the risk of flying is worth it, or if other alternatives can be considered:

    "We estimate the mortality risks caused by Covid-19 infections contracted on airplanes, taking into account that infected passengers can in turn infect others. The point estimates—which use 2019 data about the percentage of seats actually occupied on US flights--range from one death per 400,000 passengers to one death per 600,000. These death-risk levels are considerably higher than those associated with plane crashes but comparable to those arising from two hours of everyday activities during the pandemic." (1)

    I think the article makes it clear that middle seat should remain empty until the country has COVID-19 under control.

    Reference

    1. Covid-19 Risk Among Airline Passengers: Should the Middle Seat Stay Empty? https://www.medrxiv.org/content/10.1101/2020.07.02.20143826v3.full.pdf
    CONFLICT OF INTEREST: None Reported
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    Airline Transparency
    Norman Kato, MD | Avande, Inc.
    If the airlines were truly transparent, they would publish their COVID19 infections by hub by airline similar to the US state dashboards. This information is not disclosed to the flying public. Disclosure is imperative to restore confidence to flying again.
    CONFLICT OF INTEREST: None Reported
    Authors' Conflicts of Interest
    Michael Turken, MD, MPH | UCSF
    Other commenters have highlighted the absence of high quality data to support the assertions made here. There is wide variability in the implementation of safety protocols followed by different airlines. And it's clear that there is a lot we do not know still about the risk of air travel. Consequently, it's troubling to see a patient page authored by experts who have what appear to be conflicts of interest, especially when the takeaway is that the risk of contracting Covid-19 during air travel is low. The public very much deserves trustworthy and unbiased evidence to guide their decisions around the risk of air travel.
    CONFLICT OF INTEREST: None Reported
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