IMMUNIZATIONS FOR INTERNATIONAL TRAVEL

Advising international travelers on vaccine-preventable diseases is one of the major services provided by travel medicine specialists. As a consequence of political and economic instability, erosion of the infrastructure supporting public health and preventive medicine programs has occurred in many areas of the world. Outbreaks of common vaccine-preventable diseases, such as diphtheria, polio, and measles affect local populations and travelers in these areas. In addition, depending on their itinerary and activities, international travelers may be at risk for infection with the ubiquitous hepatitis A and hepatitis B viruses and may face the threat of more exotic infections, such as yellow fever, cholera, typhoid, meningococcal meningitis, rabies, and Japanese encephalitis. Indications for adult immunization with pneumococcal vaccine and influenza virus vaccine, however, are the same for travelers and nontravelers, depending on the season and the traveler's immune status, medical conditions, occupation, and age. Special categories of international travelers may be at risk for infectious diseases where vaccines are nonexistent or difficult to obtain and thus need to consider other forms of protection. Three factors influence pretravel immunization advice: risk assessment, time before departure (on the date the traveler first consults a travel medicine provider), and the traveler's budget or health insurance coverage. Known allergies to vaccines or vaccine components and other health conditions, such as pregnancy or compromised immune system, which are contraindications to live attenuated virus or bacterial vaccines, also will influence the individual's ultimate pretravel immunization plan. 4,24,26 Prioritizing vaccine recommendations based on health risk factors is a major challenge for the travel medicine advisor. Risk assessment for travel immunizations is based on the geographic destination and reported endemic and epidemic diseases; the level of anticipated contact with the local residents, flora, and fauna; and the style or conditions of travel (luxury hotels and resorts versus village accommodations and camping). For example, a major study reporting on risk for infectious diseases among Swiss travelers to Africa was published by Steffen et al and showed that the risk of hepatitis A among "trampers" was approximately 4 times higher than hepatitis A rates in typical Swiss tourists. Looking at the overall study group, however, the hepatitis A infection rate among the Swiss travelers was 100 times higher than the risk for typhoid fever and approximately 1000 times higher than the risk for cholera. 34,35 These data have been widely applied to help assess immunization priorities for travelers all over the world, especially for travelers going from more developed areas to less developed areas. Risk ratios for the various travel-acquired diseases are likely to occur at somewhat different rates among travelers from other countries going to geographic destinations outside of Africa based on culture and behavior among the particular travelers and the specific factors of medical geography at the other destinations. Unfortunately, disease reporting and surveillance systems in many countries are still developing. The accumulation of adequate surveillance data on illness rates among returned international travelers also has proved an elusive goal to date. The time available before trip departure date determines whether standard schedules for primary series of immunizations can be used in a given traveler or whether accelerated schedules should be offered. Using accelerated vaccine schedules to compress pretravel immunizations into a short time increases the likelihood that multiple vaccine doses will be given (at separate sites) on the same day. Multiple vaccine doses received on the same day may cause additive or even accentuated malaise and side effects. When departure is imminent, the question of vaccine efficacy (development of protective immunity) within a short time before exposure to the infection must be considered. Table 1 presents standard immunization schedules for commonly used travel vaccines. Rapid vaccination schedules for several travel immunizations are mentioned in the text, but health care providers should take into account that some rapid schedules are not officially approved. How much time is available in advance of the date of departure determines whether standard or rapid schedules for some vaccines can be used. A period of 10 to 14 days may be considered the minimal time to elicit a protective immune response to a given vaccination, so if less time is available before departure, it may not be worthwhile to give a vaccine, and alternative preventive measures should be considered. Besides the time needed for the recipient to form a protective immune response, there are other scheduling considerations. Some vaccines given concurrently may interfere with optimal immune responses to each, and in other cases, some vaccines given together may increase the immune response, whereas other combinations are neutral. 4,19,27,28,39 An intradermal rabies vaccine series must be completed at least 2 weeks before starting weekly chloroquine (for malaria chemoprophylaxis) to protect vaccine efficacy. If insufficient time does not permit optimum spacing, the larger intramuscular dose of rabies vaccine may be given concurrently with chloroquine without loss of efficacy. 30 The Japanese encephalitis vaccine must be completed at least 10 days before departure because of the risk for rare, delayed hypersensitivity reactions that may occur after each dose. 6 A traveler may not be able to afford or have the time to receive all the immunizations that might be of some value for a given itinerary. Travel immunizations often fall outside the range of coverage by usual health plans and insurance contracts in contrast to the routine immunizations of childhood for which boosters are recommended in adult life. The booster doses for the routine immunizations (tetanus, diphtheria, measles, and polio) usually are covered, as are pneumococcal vaccine and influenza virus vaccines for certain categories of patients. Travel vaccines are usually the financial responsibility of the traveler, and charges for the typical travel vaccines (yellow fever, hepatitis A, typhoid fever, and cholera) may amount to several hundreds of dollars and be an unwelcome surprise to the first-time traveler. Travelers whose itineraries and planned activities warrant meningococcal vaccine, rabies vaccine, or Japanese encephalitis vaccine will find the expense of these to be a major budget consideration. Travelers are advised to regard their pretravel immunization expenditures as one form of "trip medical insurance" and an investment in the overall safety of the trip.