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Public Health Agency of Canada (PHAC)
Canada Communicable Disease Report

Volume 22-17
1 September 1996

[Table of Contents]

 

The Committee to Advise on Tropical Medicine and Travel (CATMAT)* and the National Advisory Committee on Immunization (NACI)**

TRAVEL, INFLUENZA, AND PREVENTION

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, associated with influenza, are usually more common in the older population (2) and in individuals with significant concurrent medical problems. These latter groups have been traditionally targetted for the immunization programs (3,4).

The 1918 panepidemic of influenza, estimated to have killed 20 million people worldwide, inflicted a major burden of disease and death on the young and previously healthy in Canada (5,6). In the United States, it has been estimated that influenza causes millions of lost days from work (7) and 22,000 deaths per year (8). A recent evaluation supports a more widespread administration of the influenza vaccine to produce "substantial health-related and economic benefits for healthy working adults" (9).

Influenza vaccination has not been recommended for people travelling abroad other than for those for whom it is normally recommended (3,4,10). Travelling and travellers may represent an important combination of exposure to the virus and risk for influenza. In one study, "flu" symptoms were second only to gastrointestinal upset in passengers and crew on commercial air flights to the Russian Far East (11). Although the rate of influenza symptoms in this study was no greater than for 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 is usually from November to March in the northern hemispheres, and is reversed in the south (May to October). In the tropics, the virus can be isolated year around and epidemics of disease can occur at variable times of the year, including the summer months. The influenza vaccine is distributed early in the fall, usually in September, and is formulated annually based on new influenza strains predicted to arrive in Canada. Due to the reversed seasonality of influenza in the southern hemisphere, the North American formulated vaccine may not be a perfect match for those strains being transmitted in the south but will likely provide protection against some if not all of them. The vaccine is usually polyvalent. The 1996-1997 vaccine will be formulated to prevent three emerging influenza strains.

As early as the 14th century plague panepidemic (1,348 in Venice, 1,377 in Rausa, and 1,383 in Marseilles), it was recognized that the transportation of people and goods was associated with the transmission of disease (12). The early practice of "quarantine" (to hold for 40 days) was in response to this recognized threat, and eventually led to the adoption of the International Sanitary Regulations by the World Health Assembly in May 1951. In the last 45 years, significant changes in travel and transportation have occurred: more people are travelling, there are usually more individuals on a single conveyance, travel times are shorter, and distances travelled are greater, particularly by air. People are also travelling to more varied and exotic destinations.

The factors of population numbers and density, transportation speed and distance, combined with endemic disease risk and host susceptibility are creating new health-risk considerations for the traveller. Those considerations are the potential to acquire new or exotic diseases while travelling and the possibility to introduce new or exotic diseases to non-endemic areas by travellers (migrants).

Influenza outbreaks have been well described in relation to travel by train (13,14), aircraft (15), and ship (16,17). An important aspect of influenza infection while travelling is the risk that the strain of the virus will not yet have been included in current vaccines. Therefore, vaccinated persons may not be fully protected (8). Recommendations have been made to identify "high-risk" individuals who are proposing to travel abroad so that they and their eligible close contacts may be offered vaccination or post-influenza A exposure preventive therapy with amantadine or rimantadine (3,4,16,17). Detailed guidelines and recommendations for the use of these agents for chemoprophylaxis and therapy are available (4).

Chemoprophylaxis is not a substitute for prevention by vaccination except when the vaccine is contraindicated or was not given prior to the onset of influenza A activity. Special target groups in this situation would be persons at high risk for morbidity or mortality from influenza A, persons providing care to those at high risk, persons who have immune deficiency and are expected to have an inadequate response to the vaccine, and other persons wishing to avoid influenza A illness for whom a decision on chemoprophylaxis should be made on an individual basis. This may be a therapeutic option for some travellers exposed to epidemic strains of influenza A, particularly on relatively slow moving long trips, such as may occur on some ships or train tours.

From a global and societal perspective, mathematical models for regional (10,18) and global (19) influenza epidemic spread have been described. These models are based on observations of influenza spread and assumptions of population migration and viral contagiousness. The European model of epidemic influenza spread indicates that, once introduced into a susceptible population, the time available for public health intervention is probably very short, possibly < 1 month, after the first detection of an epidemic influ-enza focus (20). Such rapid spread would significantly limit the usefulness of immunization as a preventive measure.

The ability of vaccination to prevent or delay the introduction of influenza on a large-scale population basis has not been demon-strated in prospective studies. The mass movement of people within and between countries would make such a study difficult to do. Several studies have demonstrated herd immunity following influenza vaccination (21-24). Most of these studies have been done in relatively small and closed environments such as nursing homes. One study suggested that immunization increased herd immunity against influenza on a state-wide basis (24).

Summary

There are three possible objectives to immunize for influenza: 1) protection of the health of the individual; 2) prevention of outbreaks; and 3) prevention of spread from one region to another.

Given the demonstrated benefits of influenza vaccination for high-risk individuals (2,4-8), relatively cloistered populations (21-23), and now the healthy, young population (9); the observed individual risks of acquiring influenza associated with mass transpor-tation (13-17); and the potential role of rapid transportation in the spread of influenza (18-20), the following recommendations for the prevention of influenza related to travel are made.

Recommendations

  1. Routine, primary immunization against influenza, for the susceptible general population, should follow the annual recommendations of NACI (3,25) based on the predictions for endemic and epidemic influenza strains. These recom-mendations are made independently of the intention to travel. The directions for the use of the vaccine, with particular attention to contraindications and vaccine-associated adverse events, should also follow the general influenza vaccination recommendations of NACI (3).

    Evidence-based medicine category     (26) : Good evidence to support a recommendation for use. Evidence from at least one properly designed randomized, controlled study. (AI)

  2. Pre-departure influenza immunization for prevention of the disease in travellers should be considered for anyone leaving Canada during the local influenza transmission season.

    Evidence-based medicine category: Moderate evidence to support a recommendation for use. Evidence from at least one well-designed clinical trial without randomization, from cohort or case-controlled analytic studies, preferrably from more than one centre, from multiple time series, or from dramatic results in uncontrolled experiments. (BII)

  3. a. Pre-departure influenza immunization* for prevention of the disease in travellers should be offered to anyone leaving Canada who will be exposed during the influenza trans-mission season at the destination**. This may also reduce or delay the risk of introducing influenza into Canada upon returning home. This will require that a special effort is made by primary care givers and travel medicine providers to stock influenza vaccine outside of the fall months when it is usually used in Canada.

    * If the available influenza vaccine in Canada does not include the strains of virus being transmitted where and when the traveller will be at risk, obtaining the appropriate vaccine, if available and if it can be safely administered, should be considered at the destination.

    ** NOTE:     Influenza transmission seasons vary around the world. Check with the local Medical Officer of Health or other Public Health source (WHO, LCDC FaxLink (613) 941-3900) for influenza activity and transmission seasons globally. Evidence-based medicine category: Moderate evidence to support a recommendation for use. Evidence from at least one well-designed clinical trial without randomization, from cohort or case-controlled analytic studies, preferably from more than one centre, from multiple time series, or from dramatic results in uncontrolled experiments. (BII)

    b. To reduce the risk of influenza in the individual, Canadians who are abroad and will be returning to Canada from an influenza transmission zone, and who were not or could not be vaccinated against the disease before leaving Canada, should consider being vaccinated during their stay at their destination, and before returning to Canada. This inter-vention may also reduce or delay the risk of introducing influenza into Canada on their return.

    Evidence-based medicine category:     Moderate evidence to support a recommendation for use. Evidence from at least one well-designed clinical trial without randomization, from cohort or case-controlled analytic studies, preferrably from more than one centre, from multiple time series, or from dramatic results in uncontrolled experiments. (BII)

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. Canadian immunization guide 1993. 4th ed. Ottawa, Ont: Health Canada, 1993:58-63. (Supply and Services, Cat. No. H49-8/1993E.)

  4. CDC. Recommendations of the Immunization Practices Advisory Committee (ACIP). Prevention and control of influenza. MMWR 1996;45(RR-5):1-24.

  5. Pettigrew E. Flu comes to Canada, and in its wake. In: Pettigrew E. The silent enemy. Canada and the deadly flu of 1918. Saskatoon: Western Producer Prairie Books, 1983.

  6. Stevens KM. The pathophysiology of influenzal pneumonia in 1918. Perspect Biol Med 1981;25:115-25.

  7. Gross PA. Preparing for the next pandemic: a reemerging infection. Ann Intern Med 1996;124:682-85.

  8. Riddiough MA, Sisk, JE, Bell JC. Influenza vaccination: cost-effectiveness and public policy. JAMA 1983;249:3189-95.

  9. 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.

  10. Hill DR. Immunizations for foreign travel. Yale J Biol Med 1992;65:293-315.

  11. Beller M, Schloss M. Self-reported illness among travelers to the Russian Far East. Public Health Rep 1993;108:645-49.

  12. Dorolle P. Old plagues in the jet age. International aspects of present and future control of communicable disease. Br Med J 1968;4:789-92.

  13. Taylor PJ, Pocock SJ. Commuter travel and sickness absence of London office workers. Brit J Prev Soc Med 1972;26:165-72.

  14. Hogbin V. Railways, disease and health in South Africa. Soc Sci Med 1985;20:933-38.

  15. Moser MR, Bender TR, Margolis HS et al. An outbreak of influenza aboard a commercial airliner. Am J Epidemiol 1979;110:1-6.

  16. CDC. Outbreak of influenza-like illness in a tour group - Alaska. MMWR 1987;36:697-98, 704.

  17. CDC. Acute respiratory illness among cruise-ship passengers - Asia. MMWR 1988;37:63-6.

  18. Flahault A, Letrait S, Blin P et al. Modelling the 1985 influenza epidemic in France. Stat Med 1988;7:1147-55.

  19. Rvachev LA, Longini IM. A mathematical model for the global spread of influenza. Math Biosci 1985;75:1-22.

  20. Flahault A, Deguen S, Valleron AJ. A mathematical model for the European spread of influenza. Eur J Epidemiol 1994;10:471-74.

  21. 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.

  22. 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.

  23. 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.

  24. Nelson DB, Inhorn SL. Influenza surveillance of Wisconsin (USA) population-detection of A/New Jersey by isolation and serologic monitoring and vaccine evaluation. Dev Biol Stand 1977;39:429-36.

  25. National Advisory Committee on Immunization. Statement on influenza vaccination for the 1996-97 season. CCDR 1996;22:89-97.

  26. MacPherson DW. Evidence-based medicine. CCDR 1994;20:145-47.

* Members:

Dr. W. Bowie; Dr. L.S. Gagnon; Dr. S. Houston; Dr. K. Kain; Dr. D. MacPherson (Chairman); Dr. V. Marchessault; Dr. H. Onyett; Dr. R. Saginur; Dr. D. Scheifele (NACI); Dr. F. Stratton; Mrs. R. Wilson (CUSO). Ex-Officio Members: LCdr. D. Carpenter (DND); Dr. E. Gadd (HPB); Dr. B. Gushulak (Secretary); Dr. H. Lobel (CDC); Dr. A. McCarthy (LCDC and DND); Dr. S. Mohanna (MSB); Dr. M. Tipple (CDC).

** Members:

Dr. D. Scheifele (Chairman); Dr. J. Spika (Executive Secretary); N. Armstrong (Administrative Secretary) Dr. F. Aoki; Dr. P. DeWals; Dr. E. Ford-Jones; Dr. I. Gemmill; Dr. S. Halperin; Dr. B. Law; Dr. M. Naus; Dr. Y. Robert; Dr. B. Ward. Liaison Members: LCdr. D. Carpenter (DND); Dr. A. Carter (CMA); Dr. T. Freeman (CFPC); Dr. S. Hadler (CDC); Dr. D. MacPherson (CATMAT); Dr. V. Marchessault (CPS); Dr. J. Waters (ACE).

 

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