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Use of Northern Hemisphere Influenza Vaccines by Travelers to
the Southern Hemisphere
The influenza season in temperate climates extends from October through March in the northern hemisphere and
from April through September in the southern hemisphere
(1--3). Recent studies indicate that influenza viruses can
circulate throughout the year in the tropics and that influenza is the most frequently acquired vaccine-preventable disease among
those traveling to tropical and subtropical countries
(2--5). Influenza outbreaks have been reported among persons who travel
from
the northern hemisphere to the southern hemisphere and among persons from the northern hemisphere on group tours
(4--7). To reduce the risk for influenza during travel, the Advisory Committee on Immunization Practices (ACIP) recommends
that persons from the northern hemisphere who are recommended for annual vaccination or who want to avoid influenza
illness but have not yet received the 2008--09 influenza vaccine should consider being vaccinated 1) before travel to the
southern hemisphere during influenza season, 2) before travel to the tropics at any time of year, or 3) when traveling as part of a
tour group that includes persons from areas where influenza circulates during April--September (e.g., the southern hemisphere)
(8). Vaccine formulations for each hemisphere are updated yearly but might differ according to virus surveillance information
from each hemisphere.
Vaccines prepared for use in the northern hemisphere typically are administered to U.S. travelers to the
southern hemisphere, even when the vaccine formulation is less than optimal, because influenza vaccines prepared for use in
the southern hemisphere are not widely available in the United States. However, this year the influenza virus strains represented
in the 2008--09 northern hemisphere influenza vaccine currently available in the United States are identical to the
strains represented in influenza vaccines intended for use in 2009 in the southern hemisphere
(8,9).
Health-care providers should ask patients about upcoming travel plans, inform them regarding the risk for influenza
during travel, and be aware that vaccination of travelers with the currently available northern hemisphere influenza vaccine
will provide the most recently updated vaccine formulation for the southern hemisphere.
The expiration dates in the prescribing information indicate that certain lots of northern hemisphere influenza vaccines
in the United States can be used as late as June 30, 2009. If possible, influenza vaccine should be administered to travelers
a minimum of 2 weeks before departure, but can be administered up to the date of travel. No information is available
regarding the benefits of revaccinating persons before summer travel who already were vaccinated during the preceding fall
(8). In addition, before their trip, persons should learn about health risks in the destination country (information available at
http://www.cdc.gov/travel). Members of the public, especially those at higher risk for influenza complications, should consult
with their health-care practitioner to discuss the risk for influenza and other travel-related diseases before embarking on travel
(4,8).
References
Strikas RA, Kozarsky PE, Reed C, Kapella BK, Freedman DO. Should health-care providers in the United States have access to influenza
vaccines formulated for the southern hemisphere? J Travel Med 2008;15:442--6.
Camps M, Vilella A, Marcos MA, et al. Incidence of respiratory viruses among travelers with a febrile syndrome returning from tropical
and subtropical areas. J Med Virol 2008;80:711--5.
Chew FT, Doraisingham S, Ling AE, Kumarasinghe G, Lee BW. Seasonal trends of viral respiratory tract infections in the
tropics. Epidemiol Infect 1998;121:121--8.
Marti F, Steffen R, Mutsch M. Influenza vaccine: a travelers' vaccine? Expert Rev Vaccines 2008;7:679--87.
Brotherton JM, Delpech VC, Gilbert GL, et al. A large outbreak of influenza A and B on a cruise ship causing widespread morbidity.
Epidemiol Infect 2003;130:263--71.
Uyeki TM, Zane SB, Bodnar UR, et al. Large summertime influenza A outbreak among tourists in Alaska and the Yukon Territory. Clin Infect
Dis 2003;36:1095--102.
World Health Organization. Recommended composition of influenza virus vaccines for use in the 2009 southern hemisphere influenza season.
Wkly Epidemiol Rec 2008;83:366--72.
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