Measles in the United States: What Readers Should Know

What is measles?

Measles is a viral disease that passes from person to person. It can spread especially readily among people who have not been immunized. The research source says that early in an outbreak in an unvaccinated population, an infected person may pass the disease to an average of 12 to 18 others. ¹

The supplied research describes transmission and vaccination, but does not give a full account of symptoms or care. For personal health questions, readers can consult a qualified health professional or an official public health service.

What does elimination mean?

In 2000, the World Health Organization declared measles eliminated from the United States after vaccination efforts interrupted ongoing spread in the country. This did not mean the virus had disappeared from the world or that the United States could never have another case. The source says infections can arrive from places where measles remains present, including through travel. ¹

Elimination describes the interruption of sustained local spread, not protection against every future introduction of the virus. The source raises concern that the United States could lose its elimination status, but does not confirm whether this has happened. ¹

How does vaccination help?

The source describes a two-dose measles vaccination schedule, with at least one month between doses. It reports that one dose is 93 percent effective at preventing measles and two doses are 97 percent effective. ¹

Vaccination lowers the likelihood that an infection will spread through a community. Outbreaks can be harder to contain where fewer people are protected. According to the source, most people infected in US outbreaks in the 21st century were unvaccinated and lived in close-knit communities with below-average immunization rates. ¹

People with questions about their own vaccine records can ask a clinician or public health department. This explainer is not personal medical advice.

What has the outbreak history shown?

The source identifies major US measles outbreaks in 2014–2015, 2019, and 2025–2026, despite the country's elimination status. In 2015, an outbreak associated with exposure at Disneyland involved 147 cases. ¹

New York City and Rockland County also experienced outbreaks in 2018 and 2019. New York City recorded 423 confirmed cases between October 2018 and April 2019; the source identifies Williamsburg and Borough Park as areas especially affected. ¹

These events illustrate that elimination does not prevent every outbreak. The figures here reflect the periods covered by the research source, not necessarily the latest totals. The source also warns that some infections may go unreported, which means recorded case counts may not show the full extent of an outbreak. ¹