An Advisory Committee Statement (ACS)
Committee to Advise on Tropical Medicine and Travel (CATMAT)*†

Statement on Travel, Influenza, and Prevention 

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Preamble

The Committee to Advise on Tropical Medicine and Travel (CATMAT) provides the Public Health Agency of Canada (PHAC) with ongoing and timely medical, scientific, and public health advice relating to tropical infectious disease and health risks associated with international travel. PHAC acknowledges that the advice and recommendations set out in this statement are based upon the best current available scientific knowledge and medical practices, and is disseminating this document for information purposes to both travellers and the medical community caring for travellers.

Persons administering or using drugs, vaccines, or other products should also be aware of the contents of the product monograph(s) or other similarly approved standards or instructions for use. Recommendations for use and other information set out herein may differ from that set out in the product monograph(s) or other similarly approved standards or instructions for use by the licensed manufacturer(s). Manufacturers have sought approval and provided evidence as to the safety and efficacy of their products only when used in accordance with the product monographs or other similarly approved standards or instructions for use.

The World Health Organization (WHO) estimates that seasonal influenza epidemics result in up to 5 million cases of severe illness and up to 500 000 deaths a year in industrialized countries. In Canada, the annual number of deaths directly due to influenza ranges from 500 to 1 500, with many more deaths due to complications of influenza such as pneumonia. Also, influenza viruses can cause pandemics, during which rates of illness, morbidity, and mortality are greatly increased. Recent occurrences of avian influenza epidemics in poultry in Asia have resulted in subsequent transmission of avian influenza viruses to humans. Severe illnesses have been observed in connection with these outbreaks and > 75% mortality among reported cases. This experience has highlighted the importance of improving efforts to prevent the transmission of influenza viruses from avian sources and between humans.

Influenza viruses are spread from person to person primarily through droplets of secretions produced when infected persons sneeze or cough, but may also be transmitted by direct contact (e.g., through kissing, shaking hands) or by touching surfaces contaminated by infectious droplets and transferring the droplets to the mucous membranes. Influenza infection causes fever, sore throat, muscle pains, cough, lassitude, and headache. Annual attack rates average 10% to 20% but may be higher during severe epidemics⁽¹⁾. Malaise following influenza can persist for several weeks. Morbidity and mortality are more common in the older population⁽²⁾ and among individuals with significant concurrent medical problems, such as chronic obstructive pulmonary disease, reactive airways disease, congestive heart failure, diabetes, and chronic renal insufficiency. These groups have been traditionally targeted for annual pre-winter immunization programs^(3,4). There is also an increasing appreciation of the impact of influenza on young children and a greater emphasis on vaccinating this population routinely^(5,6).

The 1918 influenza pandemic, possibly the worst case scenario, was estimated to have killed over 20 million people worldwide and inflicted a major burden of disease and death on the young and previously healthy in Canada^(7,8). In the United States (U.S.), it has been estimated that annual influenza outbreaks cause millions of lost days of work⁽⁹⁾ and 20 000 deaths per year⁽¹⁰⁾. The efficacy of influenza vaccination of healthy adults⁽¹¹⁾, the elderly⁽²⁾, and long-term care home residents⁽¹²⁾ has been documented. There is also some support for a more widespread administration of the influenza vaccine to produce "substantial health-related and economic benefits for healthy working adults"⁽¹¹⁾.

Global travel likely contributes to the rapid intercontinental spread of influenza. As a result of the speed of modern transportation, even illnesses with very short incubation periods, such as influenza, may be acquired at distant locations and be transmitted when the traveller returns home. Influenza may adversely affect the quality of a vacation or the success of a business trip, and the economic impact of "travellers' influenza" may therefore be significant.

Other than for those for whom it is normally recommended, influenza vaccination has not generally been suggested for people whose only indication for the vaccine would be travelling abroad^(3,4,13). However, travelling may increase the risk of exposure to the virus and hence the risk of influenza. In one study, influenza symptoms were second only to gastrointestinal upset in passengers and crew on commercial air flights to the Russian Far East⁽¹⁴⁾. Although the rate of influenza symptoms in this study was no greater than in the general population in the U.S., the economic burden of disease due to disrupted travel, business, and vacation plans would be at least as great as in the non-traveller.

The influenza season usually runs from November to March in the northern hemisphere and the reverse in the southern hemisphere (April to October). In the tropics, the virus can be isolated year round, and epidemics of disease can occur at any time of the year. Influenza outbreaks have been well described in relation to travel by train^(15,16), aircraft^(17,18), and cruise ship^(19-26) at various times of the year. Non-travelling individuals may be exposed to travellers origin nating from different countries and, from them, to novel strains of influenza.

General protective measures

Although there is no documented evidence of the efficacy of good personal hygiene in preventing the transmission of influenza, travellers should be counselled concerning the use of this measure during travel, including frequent hand washing with soap and water or with alcohol-based sanitizing handrubs (i.e. gels or towelettes). Although recommended for the control of the spread of coronaviruses (such as the Severe Acute Respiratory Syndrome [SARS] coronavirus) in hospital settings, the use of N-95 equivalent masks for general use during travel to prevent being exposed to influenza viruses is unlikely to be effective or practical for travellers.

Vaccination

In Canada, the influenza vaccine is distributed early in the fall and is formulated annually on the basis of influenza strains predicted to circulate in the northern hemisphere in the coming season. Immunity wanes over several months, however, and older individuals in particular may have little protection remaining if they travel abroad in the spring or summer. The vaccine usually expires in June each year, and supplies are often depleted long before this time. As a result, there may not always be the option to consider vaccination in travellers after the usual influenza season. In addition, because of genetic drifts in influenza strains over time, the vaccine formulated for North America will not necessarily be a perfect match for those strains introduced from, or circulating in, the southern hemisphere. Hence, this vaccine may or may not provide protection against influenza strains encountered while travelling^(19,20). Unfortunately, southern hemisphere influenza vaccine is not available in North America during the influenza season in the south (April to October). However, travellers may wish to access this vaccine where safe, reliable products are available in southern hemisphere countries while they are travelling, if they are frequent travellers or commonly visit this region.

Unvaccinated travellers, including children, at high risk of influenza complications who would normally be recommended by the National Advisory Committee on Immunization (NACI) to obtain influenza vaccination⁽⁶⁾ should be recommended to seek pre-departure influenza vaccination, especially if they are travelling to the tropics at any time of year or to the southern hemisphere between April and October. There are no data in favour of or against the efficacy of routine revaccination (i.e., boosting) of travellers with northern hemisphere vaccine between April and October if they had already been vaccinated in the preceding fall/winter. As well, there are no data in favour of or against the efficacy of routine revaccination every 6 months of those individuals who live and travel in peri-equatorial regions of the world where influenza circulates periodically year round.

Travellers who are going to countries where human cases of SARS or avian influenza are being reported could be subjected to border checks for symptoms such as fever, and subsequently quarantined if found to be symptomatic. If travel to such destinations is essential, travellers should consider receiving influenza vaccine to reduce the likelihood of having symptomatic influenza and hence reduce the probability of failing border checks for SARS or avian influenza symptoms

Table 1. Recommendations for the prevention of influenza related to travel

Chemoprophylaxis

Recommendations have been made to identify high-risk individuals (such as organized tourist groups on cruise ships) who are proposing to travel abroad so that they and their eligible close contacts may be offered vaccination and/or post-exposure preventive therapy with amantadine or rimantadine^(3,4,19-26). Detailed guidelines and recommendations for the use of these agents for chemoprophylaxis and therapy are available elsewhere^(4,6). Oseltamivir is licensed for both the treatment and prophylaxis of influenza in Canada. Its use for prophylaxis should be considered in the event of an outbreak of amantadine-resistant influenza A or influenza B, against which amantadine and rimantadine have no efficacy^(6,27). Rimantadine is not licensed in Canada but is available in the U.S.

Post-exposure chemoprophylaxis is not a substitute for prevention by vaccination except when the vaccine is contraindicated or was not given before the onset of influenza exposure. Special target groups in this situation would be persons at high risk of morbidity or mortality from influenza, persons providing care to those at high risk, and persons who have immune deficiency and are expected to have an inadequate response to the vaccine. This may be a therapeutic option, as well, for some travellers who are symptomatic with influenza, particularly on relatively long trips such as cruises or train tours. Early therapy with antivirals is essential to reduce influenza-related morbidity.

Conclusion

Influenza immunization is our primary tool for the prevention of influenza infection and illness. Antivirals may be used for prophylaxis in people at high risk during an outbreak when vaccine is unavailable, contraindicated, or unlikely to be effective because of a poor match between the vaccine and the circulating viral strain. Antivirals may also be used as an adjunct to late vaccination of people at high risk.

There are three possible objectives for the immunization of travellers against influenza:

1. protection of the health of the individual;
2. prevention of outbreaks; and
3. prevention of spread from one region to another.

Table 1 provides recommendations for the prevention of influenza related to travel. They are based on the following: the demonstrated benefits of influenza vaccination for high-risk individuals^(2,4,12), relatively cloistered populations^(12,28-30), and now the healthy, young population⁽¹¹⁾; the observed individual risks of acquiring influenza associated with mass transportation^(15-26); and the potential role of rapid intercontinental transportation in the spread of influenza^(18,20).

Expiration

This document will be updated every 4 years or when new information becomes available.

References

1. LaForce LM, Nichol KL, Cox NJ. Influenza: virology, epidemiology, disease, and prevention. Am J Prev Med 1994;10(Suppl):31-44.
2. Nichol KL, Margolis KL, Wuorenma J et al. The efficacy and cost-effectiveness of vaccination against influenza among elderly persons living in the community. N Engl J Med 1994;331:778-808.
3. National Advisory Committee on Immunization (NACI). Canadian immunization guide 2002. 6th ed. Ottawa: Health Canada, 2002:120-7.
4. Centers for Disease Control and Prevention (CDC). Recommendations of the Advisory Committee on Immunization Practices (ACIP): prevention and control of influenza. MMWR 2003;52(RR-8):1-36.
5. Terebuh P, Uyeki T, Fukuda K. Impact of influenza on young children and the shaping of the US influenza vaccine policy. Ped Infect Dis J 2003;22(suppl 10):S231-35.
6. National Advisory Committee on Immunization (NACI). Statement on influenza vaccination for the 2004-2005 season. CCDR 2004;30(ACS-3):1-32.
7. Pettigrew E. Flu comes to Canada, and in its wake. In: Pettigrew E. (ed.) The silent enemy: Canada and the deadly flu of 1918. Saskatoon: Western Producer Prairie Books, 1983.
8. Stevens KM. The pathophysiology of influenzal pneumonia in 1918. Perspect Biol Med 1981;25:115-25.
9. Gross PA. Preparing for the next pandemic: A reemerging infection. Ann Intern Med 1996;124:682-85.
10. Lui K-J, Kendal AP. Impact of influenza epidemics on mortality in the United States from October 1972 to May 1985. Am J Public Health 1987;77:712-16.
11. Nichol KL, Lind A, Margolis KL et al. The effectiveness of vaccination against influenza in healthy, working adults. N Engl J Med 1995;333:889-93.
12. Monto AS, Hornbuckle K, Ohmit SE. Influenza vaccine effectiveness among elderly nursing home residents: A cohort study. Am J Epidemiol 2001;154:155-60.
13. Hill DR. Immunizations for foreign travel. Yale J Biol Med 1992;65:293-315.
14. Beller M, Schloss M. Self-reported illness among travelers to the Russian Far East. Public Health Rep 1993;108:645-49.
15. Taylor PJ, Pocock SJ. Commuter travel and sickness absence of London office workers. Brit J Prev Soc Med 1972;26:165-72.
16. Hogbin V. Railways, disease and health in South Africa. Soc Sci Med 1985;20:933-38.
17. Moser MR, Bender TR, Margolis HS et al. An outbreak of influenza aboard a commercial airliner. Am J Epidemiol 1979;110:1-6.
18. Klontz KC, Hynes NA, Gunn RA et al. An outbreak of influenza A/Taiwan/1/86 (H1N1) infections at a naval base and its association with airplane travel. Am J Epidemiol 1989;129:341-8.
19. Centers for Disease Control and Prevention (CDC). Acute respiratory illness among cruise-ship passengers - Asia. MMWR 1988;37:63-6.
20. Miller JM, Tam TWS, Maloney S et al. Cruise ships: High-risk passengers and the global spread of new influenza viruses. Clin Infect Dis 2000;31:433-8.
21. Centers for Disease Control and Prevention (CDC). Outbreak of influenza-like illness in a tour group: Alaska. MMWR 1987;36:697-8,704.
22. Health Canada. Influenza A outbreak on a cruise ship. CCDR 1998;24(2):9-11.
23. Centers for Disease Control and Prevention (CDC). Update: outbreak of influenza A infection - Alaska and the Yukon Territory, July-August 1998. MMWR 1998;47:685-88.
24. Centers for Disease Control and Prevention (CDC). Outbreak of influenza A infection among travelers: Alaska and the Yukon Territory, May-June 1999. MMWR 1999;48:545-6, 555.
25. Health Canada. Influenza in travellers to Alaska, the Yukon Territory, and on west coast cruise ships, summer of 1999. CCDR 1999;25(16):137-41.
26. Centers for Disease Control and Prevention (CDC). Influenza B virus outbreak on a cruise ship: Northern Europe, 2000. MMWR 2001;50:137-40.
27. Couch RB. Prevention and treatment of influenza. N Engl J Med 2000;343:1778-87.
28. Arden N, Monto AS, Ohmit SE. Vaccine use and the risk of outbreaks in a sample of nursing homes during an influenza epidemic. Am J Public Health 1995;85:399-401.
29. Patriarca PA, Weber JA, Parker RA et al. Risk factors for outbreaks of influenza in nursing homes. A case-control study. Am J Epidemiol 1986;124:114-19.
30. Gross PA, Rodstein M, LaMontagne JR et al. Epidemiology of acute respiratory illness during an influenza outbreak in a nursing home. A prospective study. Arch Intern Med 1988;148:559-61.
31. Public Health. Influenza vaccination for travellers. CMAJ 1997;156:677.

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*Members: Dr. B. Ward (Chairman); Dr. C. Beallor; M. Bodie-Collins (Executive Secretary); Dr. K. Gamble; Dr. S. Houston; Dr. Susan Kuhn; Dr. A. McCarthy; Dr. K.L. McClean; Dr. P.J. Plourde; Dr. J.R. Salzman.

Liaison Representatives: Dr. R.J. Birnbaum (CUSO); Dr. C. Greenaway (CIDS); Dr. R. Saginur (CPHA); Dr. P. Teitelbaum (CSIH).

Ex-Officio Representatives: Dr. R. Corrin (HC); Dr. B. Dobie (CIC); Dr. N. Gibson (DND); Dr. J. Given (HC); Dr. P. McDonald (HC); Dr. M. Parise (CDC); Dr. M. Tepper (DND).

Member Emeritus: Dr. C.W.L. Jeanes.

†This statement was prepared by Dr. P.J. Plourde and approved by CATMAT.

[Canada Communicable Disease Report]