The last endemic case in the Americas was confirmed in Argentina in 2009.

It took six more years to declare the disease eliminated because its symptoms are harder to detect than, for example, polio, which causes paralysis, or smallpox or measles, which cause intense, easily diagnosable rashes.

Image A poster from Chile encouraging vaccinations. The campaign to eliminate rubella was formally declared in 2003. Credit... Pan American Health Organization/WHO

Public health authorities had to review 165 million records and do 1.3 million checks to see if any communities had rubella cases. All recent cases had to be genetically tested at the C.D.C. to confirm that they were caused by known imported strains of the virus, not by quietly circulating domestic ones.

As with measles, there is no cure for rubella, but the disease is prevented by a very effective vaccine. In the United States, the shot usually contains three vaccines and is known as M.M.R., for measles, mumps and rubella.

Measles cases in the United States have surged recently because some parents who believe, contrary to scientific evidence, that the measles vaccine causes autism do not let their children receive the shot.

Endemic measles was eliminated from the hemisphere in 2002, but imported cases can surge in pockets of unvaccinated children, as happened last year in an outbreak that began at Disneyland in California.

Rubella is less contagious than measles, and the vaccine for it is somewhat more effective, so the rare imported cases have not spread as rapidly.

The rubella vaccine was first developed in 1969 by Dr. Maurice Hilleman, a prolific vaccine inventor.