Some vaccinations may be required to enter certain countries.  Other vaccinations may not be required but recommended.  Check with your local county health department and/or your family physician for suggested and required vaccinations to enter countries where you may be traveling.  Centers for Disease Control and Prevention has a comprehensive website that lists required and suggested vaccinations as well as general information on health concerns in all parts of the world, and the Allegheny County Health Department can provide you with any necessary or recommended vaccinations.

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Also, the World Health Organization has a detailed listing of problems in specific countries. If a vaccination is required or entry to your host country, make sure to have your medical care provider issue you an International Certificate of Vaccination or Prophylaxis, often as known as a Yellow Card, and keep this with your passport while traveling.  

World Health Organization