Under the International Health Regulations adopted by the World Health Organization:
A country may require International Certificates of Vaccination against yellow fever.
A cholera vaccination may be required if you are on / from an infected area.
Check you are guaranteed to health care providers or your records to other vaccines (eg tetanus and polio) up-to-date.
Prophylactic drugs for malaria and other preventative measures are recommended for travel to some countries.
No vaccinations are required to return to the United States.
Detailed health information is in Health provide information for international travel, available from the U.S. Government Printing Office for $ 20 or can at your local health office or physician or by contacting the Centers for Disease Control and Prevention, telephone are required 1-877-FYI TRIP (1-877-394-8747), toll-free autofax: 1-888-CDC-FAXX (1-888-232-3299).
You can also find the information on the CDC Web site.