Travelers should see a physician before leaving for a trip if they are going to developing countries, going off the usual tourist routes, or if they have chronic diseases that could be affected by travel. Travelers should protect themselves against common diseases that may be mild but that will disrupt their trip as well as protecting themselves against less common diseases that may be serious or even fatal. Some foreign countries require certain vaccinations before they will allow the traveler to enter the country. All travelers need to be up to date on routine vaccines they would normally get if they were not traveling (for example, an annual influenza vaccination if indicated). No vaccinations are required for re-entry into the United States for foreign travelers.