Air Travel

CDC Yellow Book 2024

Travel by Air, Land & Sea

Author(s): Tai-Ho Chen, Araceli Rey, Clive Brown

In 2019, 4.5 billion passengers took nearly 47 million international flights. The following year, annual global passenger air travel volume decreased by nearly two-thirds (1.8 billion passengers took 22 million flights), a consequence of the coronavirus disease 2019 (COVID-19) pandemic. The pandemic reversed a trend of annually increasing air travel volume, attributable at least in part to the implementation of travel restrictions by many countries.

To promote safe travel during the pandemic, in July 2020 the US Department of Transportation and other government agencies, including the Centers for Disease Control and Prevention (CDC), collaborated to publish Runway to Recovery: The United States Framework for Airlines and Airports to Mitigate the Public Health Risks of Coronavirus. Runway to Recovery was based in part on the International Civil Aviation Organization (ICAO) report and guidance document, Take Off: Guidance for Air Travel through the COVID-19 Public Health Crisis, which includes a section on public health risk mitigation measures countries can use in the travel sector. These measures, among others, helped bolster passenger and aviation worker confidence that air travel could be conducted safely during the pandemic.

Travelers often have concerns about the health risks of flying on airplanes. Although illness might occur as a direct result of air travel, it is not commonly reported. Some main concerns include exacerbations of chronic medical conditions due to changes in air pressure and humidity; relative immobility during flights leading to thromboembolic disease; and risk for infection due to proximity to others on board who could have communicable diseases.

Preflight Medical Considerations

The Aerospace Medical Association recommends evaluating chronic medical conditions and addressing instabilities prior to travel, particularly in people with underlying cardiovascular disease, diabetes, chronic lung disease, mental illness, seizures, stroke, recent surgery, or a history of deep vein thrombosis or pulmonary embolism. Travelers should be current on routine vaccinations and receive destination-specific vaccinations before travel.

Pregnant Travelers

For information on contraindications and precautions related to flying during pregnancy, see Sec. 7, Ch. 1, Pregnant Travelers.

Travelers with Disabilities

The US Transportation Security Administration (TSA) has information for travelers with disabilities and medical conditions that might affect their security screening. Travelers with Disabilities (Sec. 3, Ch. 2) includes a table of useful online resources (see Table 3-05, Online resources for travelers with disabilities or chronic illnesses). For information on traveling with a service animal, see Sec. 7, Ch. 6, Traveling with Pets & Service Animals.

Travelers Who Require Supplemental Oxygen

Travelers who require supplemental in-flight oxygen should be aware that they must arrange for their own oxygen supplies while on the ground, at departure, during layovers, and upon arrival. Federal regulations prohibit passengers from bringing their own oxygen onboard flights; passengers should notify the airline ≥72 hours before departure if they require in-flight supplemental oxygen. In addition, airlines might not offer in-flight supplemental oxygen on all aircraft or flights, and some airlines permit only Federal Aviation Administration (FAA)–approved portable oxygen concentrators. See information about screening portable oxygen concentrators at US airports.

Cabin Air Pressure & Chronic Disease

During normal flight conditions, FAA requires that commercial aircraft maintain a cabin pressure equivalent to a maximum altitude of 8,000 ft (≈2,440 m) above sea level. Cabin pressures are typically maintained at an equivalent of 6,000–8,000 ft (≈1,830–2,440 m) above sea level, but newer aircraft can maintain cabin air pressures equivalent to lower altitudes. Most travelers without preexisting health conditions will not notice any effects from the decreased partial pressure of oxygen at these cabin pressures. By contrast, a traveler with anemia (including sickle cell disease), cardiopulmonary disease (especially people who normally require supplemental oxygen), or cerebrovascular disease can experience an exacerbation of their underlying medical condition. In addition, aircraft cabin air is typically dry, usually 10%–20% humidity, which can cause dryness of the mucous membranes of the upper airway and eyes.


Barotrauma can occur when the pressure inside an air-filled, enclosed body space (e.g., abdomen, middle ear, sinuses) is not the same as the air pressure inside the aircraft cabin. Barotrauma most commonly occurs because of rapid changes in environmental pressure: during ascent, for example, when cabin pressure falls rapidly, and during descent, when cabin pressure quickly rises. Barotrauma most commonly affects the middle ear, and happens when the eustachian tube is blocked and a traveler is unable to equalize the air pressure in the middle ear with the outside cabin pressure.

Middle ear barotrauma is usually not severe or dangerous; rarely, though, it can cause complications (e.g., dizziness, hearing loss, a perforated tympanic membrane, permanent tinnitus). To help reduce the risks of barotrauma associated with cabin air pressure changes, travelers with ear, nose, and sinus infections or severe congestion might choose to postpone flying to prevent pain or injury, or use oral or nasal decongestants to help alleviate symptoms. Travelers with allergies should continue their regular allergy medications.

Travelers who have had recent surgery, particularly intra-abdominal, cardiothoracic, or intraocular procedures, should consult with their physician before flying. Travelers who participate in scuba diving should observe minimum recommended time intervals between diving and air travel to reduce the risk for altitude-induced decompression sickness (see Sec. 4, Ch. 4, Scuba Diving: Decompression Illness & Other Dive-Related Injuries, for details).

Thromboembolic Disease

Decreased mobility during travel is associated with a small but measurable increased risk for venous thrombosis and pulmonary embolism, even in otherwise healthy travelers. The overall incidence of symptomatic venous thromboembolism in the month after travel is 1 in 4,600 flights of >4 hours in duration. Risk is increased by longer flight duration and is greater in people with known risk factors (e.g., clotting disorders, estrogen use, severe obesity, pregnancy, recent surgery or trauma, previous thrombosis). The American College of Chest Physicians recommends travelers on longer flights select aisle seats, walk frequently, and perform calf muscle exercises to reduce the risk for thrombosis. People with risk factors might benefit from wearing properly fitted graduated compression stockings (15–30 mmHg at the ankle) during flight. Aspirin has not been shown to decrease risk. See Sec. 8, Ch. 3, Deep Vein Thrombosis & Pulmonary Embolism, for more details).

In-Flight Transmission of Communicable Diseases

Communicable diseases can be transmitted during air travel. People who are acutely ill or still within the infectious period for a specific disease should delay their travel until they are no longer contagious. For example, otherwise healthy adults can transmit influenza to others for 5–7 days, and transmission of respiratory viruses (e.g., measles) has been documented on commercial aircraft.

Travelers should wash their hands frequently and thoroughly or use an alcohol-based hand sanitizer containing ≥60% alcohol, especially after using the airplane lavatory and before eating meals. Some diseases spread by contact with infectious droplets (e.g., when an ill person sneezes or coughs and the secretions or droplets land on another person’s face, mouth, nose, or eyes), or when an ill person touches communal surfaces (e.g., door handles, rest room faucets) with contaminated hands. Other people handling the contaminated surfaces can then be inoculated with the contaminant. Practicing good handwashing and respiratory hygiene (covering mouth with a tissue when coughing or sneezing) can help decrease the risk for infection by direct or indirect contact.

Cabin Ventilation & Air Filtration

Large commercial jet aircraft recirculate 35%–55% of the air in the cabin, mixed with outside air. The recirculated air passes through high-efficiency particulate air (HEPA) filters that capture 99.97% of particles (bacteria, larger viruses or virus clumps, fungi) ≥0.3 µm in diameter. Furthermore, laminar airflow generally circulates in defined areas within the aircraft, thus limiting the radius of distribution of pathogens spread by small-particle aerosols. As a result, the cabin air environment is less conducive to the spread of most infectious diseases than typical environmental systems in buildings.

Coronavirus Disease 2019 & Air Travel

COVID-19 transmission during air travel has been documented. In general, COVID-19 transmission risk on aircraft remains difficult to quantify and is likely to be affected by evolving administrative, engineering, and other controls being widely implemented in the commercial air travel sector. In 2020, as described in the introduction to this chapter, US government agencies and the ICAO each developed guidance for the airline industry to use in response to the pandemic. Recommendations included maximizing total cabin airflow on commercial aircraft during both ground and flight operations; implementing surface decontamination measures aimed at reducing risk for contact with infectious droplets; and modifying passenger movement patterns before, during, and after travel.

Travelers should familiarize themselves with the latest COVID-19–related requirements when planning air travel and, as their departure date approaches, follow the guidance of corresponding health authorities. People with confirmed or suspected COVID-19 should not travel until they are no longer thought to be contagious; similarly, those exposed might need to delay travel based on their history of infection or vaccination, according to current guidance.

In-Flight Medical Emergencies

Increasing numbers of travelers combined with an ever larger percentage of older passengers make the incidence of onboard medical emergencies likely to increase. Medical emergencies occur in ≈1 in 600 flights, or about 16 medical emergencies per 1 million passengers. The most common in-flight medical events are syncope or presyncope (37%); respiratory symptoms (12%); nausea or vomiting (10%); cardiac symptoms (8%); and seizures (6%).

Although in-flight medical emergencies occur, serious illness or death onboard a commercial aircraft is rare. Death was reported in ≈0.3% of medical emergencies, ≈2/3 were due to cardiac conditions. Most commercial airplanes that fly within the United States are required to carry ≥1 approved automated external defibrillator (AED) and an emergency medical kit.

Flight attendants are trained in basic first aid procedures (e.g., cardiopulmonary resuscitation [CPR], use of AEDs) but generally are not certified in emergency medical response. Many airlines use ground-based medical consultants to assist aircrew and volunteer passenger responders in managing medical cases. In nearly 50% of in-flight emergencies, physician volunteers have assisted (see the following chapter in this section, . . .perspectives: Responding to Medical Emergencies when Flying). The Aviation Medical Assistance Act, passed in 1998, provides some protection from liability to health care providers who respond to in-flight medical emergencies.

The goal of managing in-flight medical emergencies is to stabilize the passenger until the flight can safely reach ground-based medical care. When considering diversion to a closer airport, the captain must consider the needs of the ill passenger as well as other safety concerns (e.g., landing conditions, terrain, weather). Certain routes (e.g., transoceanic flights) and availability of definitive medical care might limit diversion options.

Preparing Aircrew

To better prepare aircrew for international travel, refer to Sec. 9, Ch. 2, Advice for Aircrew. The CDC Travelers’ Health website provides current information and travel health notices. Sec. 8, Ch. 8, Airplanes & Cruise Ships: Illness & Death Reporting & Public Health Interventions, provides advice for aircrew who might encounter passengers with potentially infectious diseases. The CDC Quarantine and Isolation webpage, Airline Guidance provides requirements and tools for aircrew dealing with in-flight illness or death among passengers.

The following authors contributed to the previous version of this chapter: Paul J. Edelson, Phyllis E. Kozarsky, Clive Brown

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