Influenza vaccination for travellers
CMAJ 1997;156:677
© 1997 Canadian Medical Association
The benefits of annual influenza vaccination for patients at high risk of influenza complications and for anyone who wishes to avoid transmitting the virus to people at high risk are well known.[1] There is also evidence that annual influenza vaccination for healthy working adults is cost-effective in reducing upper respiratory infections and lost work days.[2]
Physicians and patients may be less aware of the advisability of influenza vaccination for travellers. Because influenza seasons vary around the world, travellers leaving Canada during the low-risk season can still be exposed to influenza at their destination. In temperate zones influenza epidemics tend to occur in the winter months: November to March in the northern hemisphere and May to October in the southern hemisphere.[3] In the tropics, epidemics often occur during the rainy season, but outbreaks can occur at any time of year. Because the virus has a short incubation period (13 days), exposure during travel can disrupt a business trip or vacation. For travellers at high risk of complications and those visiting regions with inadequate medical services, influenza can be dangerous. Travellers should check with their local medical officer of health or tropical diseases clinic for current information on influenza activity at their destination.
Influenza outbreaks associated with travel by train, airplane and ship have been reported.[3] However, because of the air-exhange systems used on most commercial aircraft, cabin air is likely to be less contaminated than the air on city buses or in shopping malls. Contamination of cabin air by respiratory viruses is nonetheless a possibility, especially on long flights.[4]
The US Centers for Disease Control and Prevention recommend that travellers departing for the tropics at any time of year or to temperate zones of the southern hemisphere from May to October should consider vaccination if they did not have a flu shot the previous fall or winter. Travellers who before departure receive the previous season's vaccine should be vaccinated again when the next season's vaccine becomes available.[5]
Protection begins roughly 2 weeks after vaccination and can last 6 months or more. In elderly people protective effects wane in 4 months or less. Two doses given at least 1 month apart may be necessary to obtain a satisfactory antibody response in previously unvaccinated children under age 9.[1,5] Revaccination before travel should be considered in people at high risk whose antibody levels are likely to have waned.
The most recent vaccine available at home may not cover all of the strains encountered by the traveller. If strains are known to be circulating in the destination country that are not covered by the available vaccine, the traveller should consider obtaining the appropriate vaccine after his or her arrival.[3]
Influenza vaccination has public health benefits beyond the protection of the individual person. For people leaving Canada during the influenza season, vaccination reduces the risk of introducing the virus at the destination. Similarly, vaccination before travel reduces the risk of bringing influenza back to Canada. Travellers who were not vaccinated before leaving Canada should consider vaccination before returning from a region experiencing outbreaks.[3] -- JH, AMT
References
- Statement on influenza vaccination for the 199697 season. Can Commun Dis Rep 1996;22:89-97; summarized in CMAJ 1996;155:554-5.
- Nichol KL, Lind A, Margolis KL, Murdoch M, McFadden R, Hauge M, et al. The effectiveness of vaccination against influenza in healthy, working adults. N Engl J Med 1995;333:889-93.
- Travel, influenza, and prevention. Can Commun Dis Rep 1996;22:141-5.
- Wenzel RP. Airline travel and infection [editorial]. N Engl J Med 1996;334:981-2.
- Prevention and control of influenza: recommendations of the Advisory Committee on Immunization Practice (ACIP). MMWR 1996;45(RR-5):1-24.
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