Recommendations for individuals engaging in international travel apply primarily to vaccinations and prophylactic measures for U.S. travelers planning to spend time in areas of the world where diseases such as measles, poliomyelitis, typhoid fever, viral hepatitis, and malaria occur, posing a threat to their health. In addition, some countries require an International Certificate of Vaccination against yellow fever as a condition for entry. The majority of U.S. international travelers probably do not need any additional immunizations or prophylaxis, provided their routine immunization status is up-to-date according to the standards of the Public Health Service Advisory Committee on Immunization Practices (ACIP).

The extent to which advisory statements can be made specific for each country and each disease is limited by the lack of reliable data. Although data on the occurrence of many of these diseases are published regularly by WHO, these figures represent only a small percentage of the total number of cases that actually occur. Communicable diseases are not well reported by practicing physicians, and in some countries many cases never come to medical attention. For these reasons, any recommendations must be interpreted with care.

In general, the risk of acquiring illness when engaging in international travel depends on the areas of the world to be visited—travelers in developing countries are at greater risk than those traveling in developed areas. In most developed countries (i.e., Canada, Australia, New Zealand, Japan, and western Europe), the risk to the general health of the traveler will be no greater than that incurred throughout the United States. However, a higher risk of measles, mumps, and rubella may exist. Likewise, in many developed countries such as Germany, Ireland, Italy, Spain, Sweden, and the United Kingdom, pertussis immunization is not as widely practiced as in the United States, and the risk of acquiring pertussis is greater. Living conditions and standards of sanitation and hygiene vary considerably throughout the world, and immunization coverage levels may be low. Thus the risk of acquiring disease also can vary greatly in these locations. Travelers visiting primarily tourist areas on itineraries that do not include travel or visits in rural areas have less risk of exposure to food or water that is of questionable quality. Travelers who visit smaller cities off the usual tourist routes, who spend time in small villages or rural areas for extended periods, or who expect to have extended contact with children are at greater risk of acquiring infectious diseases, because of exposure to water and food of uncertain quality and closer contact with local residents who may harbor the organisms that cause such diseases. Consequently, the added protection of booster or additional doses of certain vaccines and other prophylaxis is recommended for these persons.

More detailed comments can be found under "Specific Recommendations for Vaccination and Prophylaxis" section in this book.