Reducing the Impact of Influenza Among Travelers

DOI: 363-366 First published online: 1 November 2010

The World Health Organization (WHO) estimates that around 5% to 15% of the population is affected by the spread of annual seasonal influenza viruses, with children experiencing the highest attack rates of 20% to 30%. 1 Seasonal influenza results in between 250,000 and 500,000 deaths per year. 1 In industrialized countries, most deaths occur in people aged 65 years and above, although much less is known about the impact of influenza in developing countries. 1 Superimposed upon seasonal influenza has been a number of novel influenza viruses, including most recently a highly pathogenic avian influenza (H5N1) and pandemic (H1N1) 2009.

International travelers have a significant risk of acquiring influenza infection. Among travelers to tropical and subtropical countries, the estimated risk is 1% per month. 2,3 Risk is not limited to those visiting tropical and subtropical countries; leisure and business travelers to any temperate country during influenza season can also be infected, and travelers may encounter it from other travelers coming from areas affected by seasonal influenza, such as on cruise ships. 4,5 Domestic travelers are also at risk when traveling within their home country during the influenza season. 4 Air travel itself probably plays an important role in the spread of annual seasonal influenza, 6 and spread of influenza to passengers on airplanes has been clearly documented. 7–10 The initial spread of pandemic (H1N1) 2009 closely matched the volumes of international passenger movements. 11

According to the World Tourism Organization (WTO), together with the Global Financial Crisis, pandemic (H1N1) 2009 probably contributed significantly to a 4% drop in international tourist arrivals to 880 million in 2009. 12 In Australia, the first cases of pandemic (H1N1) 2009 were reported in early May, which coincides with the beginning of the annual influenza season. 13 Although cases of pandemic (H1N1) 2009 were occurring globally, climatic factors influence the spread of influenza, and the perspective of Australians' planning outbound international travel from the southern hemisphere to the northern hemisphere may have been different from travelers going from a summer to a winter climate. Even during the height of pandemic (H1N1) 2009, Australians' international travel plans were virtually unaffected, with seasonally adjusted estimates of short‐term resident departures showing minimal change in May and June 2009, and a 10% increase in July 2009. 14,15 By contrast, short‐term visitor arrivals to Australia decreased in May to July 2009. 14,15 As of September 10, 2010, in Australia, sentinel surveillance data suggests that influenza activity remains moderate, with a significant number of cases of pandemic (H1N1) 2009 reported, with the region being described by the WHO as one of the most intense areas of influenza transmission at present. 16

The emergence of avian influenza and more particularly the advent of pandemic (H1N1) 2009 have highlighted a number of issues regarding influenza and travel. Firstly, effective public health messages and risk‐reduction measures need to be simple. During pandemic (H1N1) 2009, measures instituted included entry screening to help delay the local transmission of pandemic influenza, 17 social distancing, immunization, and most importantly general hygiene measures such as hand washing. 2,13 These preventive measures are fairly consistent with those outlined by the WHO for both seasonal and pandemic (H1N1) 2009. 4 Such measures are particularly important for travelers, who fall into higher risk categories. 2 Of note, evidence does not support air travel restrictions as an effective intervention to alter the course of seasonal influenza spread or of an influenza pandemic. 6

Secondly, two major factors that need to be considered in relation to influenza and travel are travelers' knowledge regarding influenza infection and related preventive measures, as well as their perception of risk. Specific educational efforts to improve knowledge about influenza and appropriate precautionary actions can be effective. 18,19 However, even successful educational campaigns are unlikely to translate to increased compliance with precautionary recommendations if people do not perceive that they are at high risk of significant morbidity from infection. Consequently, risk perception poses a significant challenge to more widespread adoption of preventive measures including pre‐travel influenza vaccination. 20 A study performed soon after the initial reports of avian influenza (H5N1) spreading in wild and domestic birds showed that Australian hostellers were moderately concerned about the possibility of increasing human‐to‐human transmission. 18 Another study of travelers during pandemic (H1N1) 2009 indicated that over half had some level of concern about this disease outbreak when traveling. 21 Despite this, nearly two thirds of travelers indicated they would not alter their travel even in the face of influenza‐like symptoms. 21 Among over 900 European travelers during winter 2009 and winter 2010, risk perception regarding influenza was low, and both seasonal and pandemic influenza vaccination coverage rates were poor (13.7 and 14.2%, respectively). 20 The study by Yanni and colleagues in this edition of the journal further supports this: the majority of US travelers to Asia who were surveyed during the H5N1 avian influenza outbreak were aware of appropriate influenza prevention measures, yet 57% believed they did not need to be vaccinated and less than half had received an influenza vaccine in the previous 12 months. 22

Together, these factors imply that multiple complementary efforts will be needed to reduce influenza risks and increase vaccine coverage among travelers 20 involving simple educational and public health messages, risk evaluation, and better risk communication. In the context of travelers, this means that family physicians and travel medicine practitioners will need to intensify their strategies for informing travelers about their individual risks of infection.

Innovative strategies to target specific travel groups should also be considered. The study focusing on European business travelers reported by Helfenberger and colleagues suggests that business travelers comprise an eligible target group for investigation of knowledge and practices regarding influenza, both because of their frequent travel patterns and because surveys can be disseminated via large employer groups. 23 By inference, there may also be a group for which information and risk communication regarding influenza could be quite easily facilitated, both among employers and employees. Another study among European business travelers showed that this group was significantly less likely to have received influenza vaccination during winter 2009/2010 (odds ratio = 0.39, 95% CI: 0.17–0.92) than other travelers. 20 However, a recent Finnish study showed that business travelers are less likely to accept risks associated with travel than are tourist travelers, perhaps indicating that individuals traveling for business could be particularly receptive to pre‐travel influenza messages. 24

As highlighted by Helfenberger and colleagues, 23 a potential contributory factor to the poor vaccination uptake by travelers may be the non‐uniformity among international travel advisory guidelines regarding indications for influenza vaccination. If messages from advisory groups are contradictory, this can be confusing both for health professionals providing pre‐travel advice and for travelers. The WHO recommends that those travelers at higher risk traveling to the opposite hemisphere should have influenza vaccination. 4 This is fairly consistent with WHO population‐based recommendations for influenza vaccination. 1

It is generally accepted that influenza immunization should also be considered for cruise ships, group tours, and during other mass gathering events. 25 However, apart from the general recommendations for travelers in high‐risk population groups, specific recommendations for travelers are hard to come by.

In Canada, the Committee to Advise on Tropical Medicine and Travel (CATMAT) has recommended influenza vaccination for all healthy travelers, who will or could be exposed to influenza at the destination. 26 In the United States, the Centers for Disease Control and Prevention's (CDC's) Advisory Committee on Immunization Practices recently voted in favor of universal influenza vaccination in that country. 27 There a number of useful influenza surveillance resources, which have been listed in Table 1. Not only is there variability in approaches for who should be vaccinated but a variety of influenza vaccines are available, including vaccines administered by the intramuscular, intradermal, and intranasal routes.

View this table:
Table 1

Global influenza surveillance resources

ResourceWebsite *
WHO FluNet
WHO, global alert and response, influenza
CDC, seasonal influenza
Public Health Agency of Canada, FluWatch
http://file:// Flu trends
  • WHO = World Health Organization; CDC = Centers for Disease Control and Prevention; EISN = European Influenza Surveillance Network.

  • *All websites last accessed July 31, 2010.

Another issue often raised when discussing influenza vaccination is that influenza viruses constantly evolve, and influenza vaccines need to protect against the principal strains of virus circulating at the time. 4 These can differ between the northern and southern hemispheres and influenza vaccinations are modified approximately every 6 months in preparation for the peak influenza season in each hemisphere. 4 Hence, an influenza vaccine from one hemisphere may only partially protect against the virus strains in the other hemisphere, depending on the constituent virus strains covered. 4 There is a vaccine available for pandemic (H1N1) 2009, but not for avian influenza (H5N1). 4 There is interest in making southern hemisphere seasonal influenza vaccines available to providers in the northern hemisphere and vice versa, but practical difficulties need to be overcome. 28,29

Guidelines for chemoprophylaxis and presumptive self‐treatment for influenza also differ among international travel advisory groups. Antiviral drugs are an important adjunctive preventive measure for the treatment and prevention of influenza, 1 including pandemic (H1N1) 2009. 13 There are two main classes of influenza antiviral agents, M2 inhibitors and neuraminidase inhibitors, 30 although the older M2 inhibitor drugs have not been widely recommended due to their high potential for resistance. Oseltamivir, a neuraminidase inhibitor, can shorten illness caused by influenza by up to 1.5 days if commenced within 48 hours of symptom onset, and it can therefore be used by travelers for presumptive self‐treatment of flulike symptoms. For some high‐risk travelers, oseltamivir prophylaxis may also be considered. This can be begun either on arrival at the destination or after a suspected exposure. 30 However, there is no clear guidance on appropriate uses of antivirals among travelers, and opinion regarding specific indications may vary according to the predicted incidence, morbidity, and mortality of the annual circulating influenza species. Two factors that argue against the widespread use of oseltamivir by travelers are emerging resistance 31,32 and the fact that travelers should be wary of self‐treatment of influenza‐like illnesses with antiviral medications alone, especially when traveling in malarious areas, as a malaria diagnosis should be considered in any febrile illness. 30

Given the recent heightened interest in influenza, it is conceivable that now more than ever travelers (and non‐travelers) might respond to public health messages regarding influenza prevention, or they might deliberately boycott such messages, claiming that public health and the industry exaggerated the risk of influenza. Devising suitable educational messages for travelers about influenza prevention requires information about their baseline influenza knowledge and their perspectives regarding risk. The studies in this issue provide useful information regarding attitudes and practices to influenza prevention among travelers from the United States to Asia and business travelers, respectively. 22,23 They also suggest that, in addition to more widely promoting WHO recommendations for general hygiene precautions for the prevention of influenza, guidelines for seasonal and novel influenza virus prevention need to be clarified internationally. Ideally there should be uniform guidance among international advisory groups, focusing on both traveler vaccination and on carriage and use of antiviral medications.

Declaration of interests

P. A. L. has received fees for consulting and/or serving on an advisory board from GSK and was paid travel to attend symposia and/or conferences by GSK and Sanofi Pasteur.

K. L. states she has no conflicts of interest to declare.


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