The risk for exposure to influenza during travel varies depending on the time of year, destination, and type of travel. In the tropics, such as the Caribbean, influenza can occur throughout the year. In temperate regions of the Southern Hemisphere, such as parts of Australia and South America, most influenza activity occurs from April through September. In countries of the Northern Hemisphere, such as the United States and Canada, influenza generally occurs from November through March. However, in temperate climate zones of the Northern and Southern Hemispheres, travelers can be exposed to influenza during their respective summer months, especially when traveling as part of large, organized tourist groups composed of persons from areas of the world where influenza viruses are circulating.

From 1997 through 1999, CDC investigated three summertime influenza outbreaks among large, organized tourist groups in North America. One outbreak occurred among travelers on a cruise ship during the late summer, and the other two outbreaks) occurred predominantly among travelers on combined land and sea tours in Alaska and the Yukon Territory. Also in 1999, CDC identified clusters of influenza infection among travelers in the Caribbean region during the spring and in the Mediterranean region during the summer. Similarly, in 2000, another summertime influenza outbreak was identified on a cruise ship in northern European waters. These outbreaks suggest that tourists traveling in large groups might be at increased risk for exposure to influenza viruses throughout the year.

Exposure to influenza virus during travel can result in clinical illness that begins while traveling. Influenza illness might be, at best, an inconvenience; however, it can lead to complications, including life-threatening pneumonia, especially among persons at increased risk for complications (such as those aged 50 years or older and persons of any age with chronic medical conditions, such as heart or lung diseases). Annual influenza vaccination is the primary method for preventing influenza and its complications.

Groups at increased risk for influenza-related complications who should receive influenza vaccination include:

persons aged 50 years or older;
residents of nursing homes and any other chronic-care facilities that house persons of any age who have chronic medical conditions;
adults and children who have chronic disorders of the pulmonary or cardiovascular systems, including children with asthma;
adults and children who have the following medical conditions:
chronic metabolic diseases (including diabetes mellitus),
renal dysfunction,
hemoglobinopathies,
immunosuppression (including immunosuppression cause by medications and by human immunodeficiency virus);
children and teenagers (aged 6 months to 18 years) who are receiving long-term aspirin therapy and therefore might be at risk for developing Reye syndrome after influenza infection;
women who will be in their second or third trimester of pregnancy during the influenza season.

To decrease transmission of influenza virus to those at risk for influenza-related complications, vaccination also is recommended for people who are in close or frequent contact with at-risk persons. They include:

health care providers;
employees of nursing homes and chronic-care facilities who have contact with patients or residents;
providers of home care to persons at high-risk;
household members (including children) of persons in high-risk groups;
emergency response workers.
Persons of any age who wish to decrease their chances of influenza infection also may be vaccinated.
The following travelers should consider receiving influenza vaccine at least 2 weeks before travel if they were NOT vaccinated during the most recent fall or winter:

anyone at high-risk for influenza-related complications;
anyone who wishes to decrease his or her chances of developing influenza IF:
traveling to the tropics at any time of year,
traveling to the Southern Hemisphere from April through September,
traveling with large, organized tourist groups at any time of year.
No information is available regarding the benefits of revaccinating persons before summer travel who were already vaccinated the preceding fall or winter.

Persons at high-risk who received the previous season's vaccine should be revaccinated before travel in the fall or winter with the current vaccine. Because the availability of influenza vaccine is limited during the summer in North America, persons aged 50 years or older and others at high-risk for complications should consult their physicians before embarking on travel to discuss the risks of influenza and the advisability of carrying antiviral medications for either prophylaxis or treatment of influenza infection.

© Center for Disease Control

Credits: National Center for Infectious Diseases