American Journal of Law & Medicine

Vaccines and Airline Travel: A Federal Role to Protect the Public Health

This Article explores two ways in which airline travel is an important vector for the spread of infectious disease, and argues that airlines have market-based and liability-based reasons to require that passengers be vaccinated. Going further, the Article explores whether the federal government has the legal and constitutional authority--especially under the Commerce Clause--to encourage or mandate that airlines implement such a vaccine screen. By disrupting the spread of disease at key network nodes where individuals interact and then connect with other geographic regions, and by creating another incentive for adult vaccination, an airline vaccine screen could be an effective and legally viable too! for the protection of public health.

     1. The Duty to Screen
     2. The Duty Not to Discriminate
     3. Other Elements for Liability


For a wide range of highly contagious and dangerous diseases, the Food and Drug Administration ("FDA") has approved safe and effective vaccines, which the Centers for Disease Control and Prevention ("CDC") now routinely recommends. (1) With the eradication of smallpox worldwide in 1977, the eradication of polio in the United States in 1979, and the 100,000-fold reduction in the prevalence of diseases like diphtheria, measles, mumps, and pertussis, the success of vaccines cannot be disputed. (2)

However, the rates of vaccination have been insufficient to eradicate some diseases. (3) "Approximately 42,000 adults and 300 children in the United States die each year from vaccine-preventable diseases." (4) On the horizon are new vaccinations, which may address avian flu, H5N1 influenza, H1N1 influenza, norovirus, Ebola, and tuberculosis. (5) Moreover, it will soon be possible to invent a new vaccine to fight a disease outbreak as it is happening. (6)

For all these diseases, the solution to morbidity and mortality is not merely technological--it depends on human behavior. Without high levels of vaccination, these infectious diseases will remain a significant threat.

In the American tradition of federalism, state and local governments have exercised the plenary "police power," which includes the primary responsibility to secure the public health and, in particular, to fight infectious diseases. (7) Accordingly, much of the legislative action and litigation around vaccines has focused on state mandates to vaccinate children as a prerequisite for their attendance at schools. (8) These state mandates vary widely in the ease by which parents may exempt their children and, consequently, the rates of vaccination and the risk of contagion differ across the United States. Even more, these mandates have no direct effect on the vaccination rates of adults and do little to address the movement of unvaccinated individuals across state or international borders.

Adult vaccination has become increasingly important. (9) In the near future, when a new vaccine is quickly developed to respond to a specific outbreak of a more exotic disease, adult vaccination may be essential. It may not be sufficient to rely on school vaccinations and the smattering of adult vaccination programs, such as those for healthcare workers. Nor will an optimal adult vaccination strategy be random. It will instead follow the same human network of interactions that spread disease, targeting nodes in which a vaccination may have the greatest disruption of the transmission of disease. (10)

Airports and airlines are arguably one of the most important nodes. On average, Americans take 2.1 airline trips each year. (11) The United States airlines move approximately two million people every day. (12) If unvaccinated, these travelers are more likely to carry infectious diseases with them. This problem can be viewed as one of externalities, flowing across jurisdictional borders: a state's sovereign prerogative to have robust vaccination laws that protect its residents is undermined if unvaccinated individuals from other states cross its borders daily. (13) Because vaccines can only provide imperfect protection to those who receive them, and some individuals are unable to be vaccinated at all (due to other medical problems), those who choose to be unvaccinated pose a public health threat. (14)

Leading voices in public health law have warned about cramped legal conceptions of federalism, which may undermine the government's ability to protect its citizens. (15) Of particular concern is NFIB v. Sebelius, a recent United States Supreme Court decision. The Court held that the Commerce Clause of the United States Constitution does not support a congressional mandate requiring individuals to purchase health insurance. (16) Some have argued that this decision, and the larger conception of federalism it represents, erodes the constitutionality of core public health functions of the federal government. (17) A vaccination mandate, tracking the channels and instrumentalities of interstate commerce, may reinvigorate Commerce Clause doctrine for public health.

This Article is the first scholarly assessment of three issues: (1) whether airline travel is itself an important vector for the spread of infectious disease; (2) if so, whether airlines have market-based and liability-based reasons to require that passengers be vaccinated; and, (3) whether the federal government has the legal and constitutional authority to either encourage or mandate that airlines do so. The scientific literature suggests that by disrupting the spread of disease at key network nodes where individuals interact with each other and then connect with other geographic regions, a vaccine screen could be an effective tool for the protection of public health. (18) The legal analysis suggests that a vaccine screen could be a legally viable tool for the protection of public health, falling squarely within the authority of the federal government.

Of course, vaccinations are not our only tool to address the problem of air travel and infectious disease. (19) In particular, the CDC maintains a "Do Not Board" list, which prohibits certain individuals from flying domestically or internationally if they have a communicable disease that presents a public health risk. (20) A primary limitation of such policies is that they are only effective for patients that have become symptomatic and have received a diagnosis that was passed on to the CDC for a decision about whether to list the person. For contagious but asymptomatic people, or symptomatic people who have not yet received a diagnosis, the Do Not Board list is ineffective. Another possibility is to use body scanning technologies or simple contact thermometers to attempt to identify infected persons who may have higher body temperatures, but this strategy also has practical limitations, raising many false positives and false negatives. (21)

For the purposes of this initial foray into the question, let us remain agnostic about the particular vaccines that would be included in such a screening policy (whether for measles, influenza, or Ebola), the logistics of implementing such a screen (including the documentation required, ranging from documented immune response to a vaccine registry to a simple affirmation under penalty of perjury), and the scope and procedures for any potential exemptions (medical, religious, or philosophical). These variations will be important practically, politically, and legally, but a more general analysis is useful to frame the question.


Consider three mechanisms by which air travel may affect the spread of infectious disease. First, passenger-to-passenger transmission by contact (i.e., touching, coughing, sneezing, etc.) is increased during air travel. Second, regardless of what happens between passengers on the airplane, the air travel of infected passengers is an extremely efficient mechanism for rapidly distributing a disease across state borders and worldwide. This Article proposes a third, novel mechanism for air travel to reduce the spread of infectious disease. If airline travel were the predicate for a vaccination mandate, it could serve as an important incentive for people to get vaccinated, thereby creating spillover benefits beyond the domain of air travel.


The popular media portrays airline travel as if it were a journey into an apocalypse, with disease at every turn. One headline reads: Horrific Hygiene On Flights Revealed: Poo On Tray Tables, Urine On Seats And 80 Million Bacteria Living On Your Suitcase. (22) CNN reports that some tray tables are infected with MRSA (Methicillin-resistant Staphylococcus Aureus) at five times the rate of New York subway poles, and warned about the airplane "lavatory as a major danger area for the spread of disease during the H1N1 flu and SARS epidemics." (23) Mass media often cites survey data, which suggests that flying on an airline dramatically increases--by over 100 times--the chances that an individual will be infected with any of the roughly 200 viruses known to produce the common cold. (24)

The scientific literature is more sober and relatively undeveloped, but it leaves grounds for concern. (25) Means of microorganism transmission can be organized into four main categories: contact, airborne, common vehicle, and vector borne. (26) Contact transmission includes both direct and indirect body-to-body contact, as well as transmission by large droplets spread by an infected person sneezing, coughing, or talking. (27) Of concern to air travelers are those diseases that are airborne and spread by contact, such as diphtheria, pertussis, pneumococcal disease, various forms of influenza, poliovirus, measles, mumps, rubella, varicella, tuberculosis, meningococcal disease, SARS, smallpox, and Ebola. (28) Diseases with fecal-oral transmission can also be of concern to air travelers, but this is more likely to occur as the result of airlineassociated spread through food served on board. (29)

Airlines recycle about fifty percent of the cabin air, which would seem to be an obvious vector for disease delivery. (30) However, airlines usually filter and deliver the air vertically, from the ceiling of the cabin, drawing it downward and out, before filtering it and mixing it with fresh air. (31) Thus, the scientific literature suggests that when the ventilation system is working properly, air quality probably does not contribute significantly to the passenger-to-passenger transmission of infectious diseases. (32) Nonetheless, "[transmission becomes widespread within all sections of the passenger cabin when the ventilation system is nonoperational, as shown by an influenza outbreak when passengers were kept aboard a grounded aircraft with an inoperative ventilation system." (33) Scientists have also expressed worry that the low levels of humidity aboard an aircraft may dry out the passengers' mucous membranes, which undermines the body's natural ability to capture and destroy viruses and bacteria. (34)

Transmission of diseases spread by contact--which includes large respiratory droplets from sneezing, coughing, or talking--is more worrisome. (35) Tuberculosis is the most studied disease for spread aboard an aircraft; documented cases include a passenger traveling between three American cities and infecting the skin of four of fifteen fellow passengers but not leading to any cases of active disease. (36)

The greatest "risk of disease transmission is associated with a flight time of more than 8 [hours] and sitting within two rows of the index passenger." (37) There have been reports, however, of diseases spreading more extensively. Measles infections, for instance, have been shown to spread to patients as far as sixteen rows away. (38) In another measles outbreak, an infected patient appeared to have infected another person flying on the same aircraft, as well as five other people who had merely "visited at least one common departure gate." (39) On the other hand, over the course of a seven hour flight from Japan to Hawaii, a passenger with measles caused zero infections in 336 exposed passengers, presumably because the vast majority were immunized. (40)

There have also been various examples of transmission of SARS onboard an aircraft. (41) Physical proximity to the infected person during the flight was clearly correlated to risk of transmission. (42) In one example, a flight attendant was infected after interacting with and touching the tray and food of an infected person. (43) In another case, one infected person on a flight of 119 people was associated with potential transmission to twenty-two fellow passengers. (44)

Norovirus was also probably transmitted passenger-to-passenger on an airplane, but by a different mechanism: contamination of the restrooms. (45) Due to the specific epidemiology of norovirus, and because vomiting was contained to the restrooms, it is unlikely that airborne droplets were the cause of transmission. (46) Interestingly, all passengers suspected of norovirus infection reported that the restrooms were clean. (47) This suggests that maintenance for the prevention of disease transmission requires more than apparent cleanliness.

The flu has similarly been documented to spread aboard airline flights. A 1972 outbreak of influenza A/Texas strain on a plane, where passengers were kept aboard for three hours without an operable ventilation system, "resulted in 72% of all passengers about the airline contracting influenza within [three days]." (48) The illness then spread to twenty percent of their family members within two weeks. (49) Other cases of influenza contamination on airplanes have involved patients seated as far as five rows away from the patient who brought the disease on board. (50)

Finally, in addition to the accidental spread of disease person-to-person, there are real concerns that airline flights could be an efficient way to distribute bioterrorism agents among hundreds of people in very close vicinity. Smallpox is particularly worrisome in this regard. In one outbreak in Sweden the spread of smallpox was linked to an in-transit exposure that led to "24 secondary cases and four deaths." (51)

In short, although the person-to-person spread of disease is not peculiar to airline travel, this context intensifies this risk factor. There are few other instances in modern social life where an individual person is in such closely proximity to strangers for such an extended period of time while eating, drinking, and using the restroom. On the other hand, with vaccination, widespread immunity to a disease will limit its spread, even in these close quarters. (52)


"Perhaps the greatest concern for global health ... is the ability of a person with a contagious illness to travel to virtually any part of the world within 24 [hours]." (53) After the terrorist attacks of September 11,2001, the ban on airline travel and the subsequent depression of the air travel market provided a natural experiment that demonstrated how air travel contributed to the rate at which a disease spreads across the country. (54) We now know that the volume of travel is directly related to the rate at which influenza viruses spread within the United States. (55)

There are documented cases of measles being spread around the country in this way. For example, in 1982 a young naval officer from San Diego acquired the disease from a two-year-old child there, and then traveled to Washington State, where he then infected nine others. (56) Only one of these individuals met him face-to-face; the others were infected because they were on the same flight or in the same parts of the airport. (57) More recently, a single outbreak of measles at Disneyland was then spread across the country by travelers, creating 189 cases, spread across twenty-four states and the District of Columbia. (58)

"The severe acute respiratory syndrome (SARS)," which caused 774 deaths, "spread rapidly around the world, largely because persons infected with the SARS-associated coronavirus ("SARS-CoV") traveled on aircraft to distant cities." (59) As the CDC explains in its retrospective, "SARS, for the United States, was a travelassociated illness." (60)

On an international scale, the spread of H1N1 has been correlated to the volume of international flights to and from a destination. (61) The implication of this study is that commercial airports can be mapped and the connections can be used as a means of limiting the spread of infectious diseases in the future. (62) Another study, also looking at H1N1, reached a similar conclusion: the volume of international traffic of a United States airport can be used to predict the United States arrival time of a disease based on the disease's point of origin. (63)

Similarly, Ebola was spread from West Africa and brought to and around the United States by airline travel, where the first patient then infected two healthcare workers. …

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