evidence: Measles is an airborne, extremely infectious, and potentially severe rash illness. Before the measles vaccine was introduced, an estimated 48,000 people were hospitalized and 400–500 people died in the United States each year. [...] The measles, mumps, and rubella (MMR) vaccine is very safe and effective. When more than 95% of people in a community are vaccinated (coverage >95%), most people are protected through community immunity (herd immunity). However, vaccination coverage among U.S. kindergartners has decreased from 95.2% during the 2019–2020 school year to 93.1% in the 2022–2023 school year, leaving approximately 250,000 kindergartners at risk each year over the last three years. To dive into vaccine coverage data for MMR, visit VaxView. [...] This is the greatest number of cases reported in the United States since 1992. The majority of cases were among people who were not vaccinated against measles. Measles is more likely to spread and cause outbreaks in U.S. communities where groups of people are unvaccinated.