Travel-related vaccines.

Travelers are at increased risk for several infections, including familiar infections such as measles that are widely distributed but more common in developing countries. Vaccines can markedly decrease the risk for many of these infections and are an important part of pretravel preparation. Travel provides an opportunity to review and update routine vaccines in adults and assess risk from unusual infections. Global travel is growing. Persons who are elderly, HIV-infected, and immunocompromised account for many of the travelers. Studies that assess the immunogenicity, efficacy, and adverse effects of some of the special vaccines used primarily in travelers generally have been done in young, healthy populations. Findings in young adults do not apply to other populations in whom immune response can be slower, less effective, and less durable. Recent reports of severe adverse events in elderly persons who have received yellow fever vaccine are a reminder that widely used, old vaccines can have unexpected side effects when used in a new population. It is biologically plausible that adverse effects might be more common in the elderly, and epidemiologically plausible that occasional instances of similar adverse events in the past could have been missed. Studies on special and travel vaccines in the elderly are needed urgently to define how these vaccines should be used in older populations and whether alternative means for protection are needed.