Elimination of endemic measles in the United States

In the first decade of national reporting, an average of 6,000 measles deaths were reported in the United States each year. In the decade before a vaccine arrived in 1963, measles still infected an estimated 3 to 4 million people in the United States each year, sent about 48,000 to hospital and killed 400 to 500. Vaccination cut those numbers, but one dose did not end outbreaks. In 1989 measles spread among vaccinated school-age children, and a second dose of measles, mumps and rubella (MMR) vaccine was recommended.

By 2000 first-dose coverage among preschool children had been above 90 percent for four years, and by 2002, 49 states required two doses for school-aged children. That year the country recorded 86 confirmed cases. Twenty-six had been imported from abroad, and importation-associated cases made up 62 percent of the total. CDC wrote that the consistently small number of cases with no known source suggested measles was no longer endemic in the United States, and elimination was declared in 2000.

Elimination has a narrow meaning: the absence of endemic transmission for more than 12 months in a defined area where surveillance works well. Imported cases still occur, and the status has to be kept. Two prolonged outbreaks in undervaccinated communities in New York in 2018 and 2019 threatened it, and more than 1,200 cases were reported in 2019, the most since 1992. Reviewing 20 years of data in 2022, Adria Mathis and colleagues concluded that epidemiological and laboratory evidence supported continued elimination, which they credited to high coverage with two doses of MMR vaccine.