Yellow fever vaccine is a live-virus vaccine which has been used for several decades. A single dose protects against disease for 10 years or more. If a person is at continued risk of infection, a booster dose is recommended every 10 years. See this page for caveats, etc.

As well, note:

Vaccine Administration

For all eligible people, a single injection of reconstituted vaccine should be administered subcutaneously. Revaccination has been required by certain countries at 10-year intervals to comply with International Health Regulations (IHR) of the World Health Organization (WHO).

Note: In February 2015, the CDC Advisory Committee on Immunization Practices (ACIP) approved a new recommendation that a single dose of yellow fever vaccine provides long-lasting protection and is adequate for most travelers. The updated recommendations also identify specific groups of travelers who should receive additional doses and others for whom additional doses may be considered. The official ACIP recommendations were published on June 19, 2015 (see http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6423a5.htm). All current ACIP yellow fever vaccine recommendations can be found on the ACIP website at: http://www.cdc.gov/vaccines/hcp/acip-recs/index.html.

Although ACIP no longer recommends booster doses of yellow fever vaccine for most travelers, clinicians and travelers should review the entry requirements for destination countries because changes to the International Health Regulations (IHR) have not yet been fully implemented. In 2014, the World Health Organization adopted the recommendation to remove the 10-year booster dose requirement from the IHR as of June 2016. Once this change is instituted, a completed International Certificate of Vaccination or Prophylaxis will be valid for the lifetime of the vaccinee. Some countries have already adopted this change, which is noted under the yellow fever vaccine requirements on each country’s destination page. However, it is uncertain when and if all countries with yellow fever vaccination requirements will adopt this change. (Updated August 26, 2015)