Eradication refers to a disease being completely, literally eradicated from the earth: no cases occur at all, from any source. Elimination refers to a permanent interruption in indigenous transmission of a disease, making it no longer endemic, but the disease can still be introduced by a case from another geographical region.
Deeper dive
Vaccines led to the elimination of polio in the United States in 1979 and measles in 2000. Yet measles cases still occur in the U.S. and in July 2022, New York state health officials reported the nation’s first polio case in a decade in an unvaccinated individual. The key here is that “elimination” and “eradication” are different things, though they are often confused by readers and sometimes even by journalists.
Eradication refers to a disease being completely eradicated from the earth. The best-known example is the eradication of smallpox in 1980. Elimination refers to a permanent interruption in disease transmission, making it no longer endemic. The disease can still be introduced by a case from another geographical region, like travel.
For example, there have been numerous outbreaks in the U.S. introduced by a person visiting from outside the U.S. None of them began with a person already living in the U.S. because the virus no longer circulates on its own in the U.S., due to the measles vaccine.
The distinction is important because an eliminated disease can always return if conditions allow for it, such as a sufficiently deep, sustained decline in vaccination rates, which is what allowed measles to circulate again in certain communities.