A highly contagious viral disease that was declared eliminated in the U.S. in 2000 but continues to cause outbreaks due to declining vaccination rates.
Measles (rubeola) is a highly contagious viral infection caused by the measles virus, a paramyxovirus. It is one of the most infectious known diseases, with an R0 (basic reproduction number) of 12-18, meaning that one infected person can transmit the virus to 12-18 others in a completely susceptible population (CDC, 2024).
Before the introduction of the measles vaccine in 1963, an estimated 3-4 million people contracted measles annually in the United States, resulting in 400-500 deaths. The vaccine led to a 99% reduction in measles cases in the U.S. The disease was declared eliminated in 2000, meaning there was no continuous transmission for more than 12 months (CDC, 2024).
However, measles remains endemic in other parts of the world, and importations continue to occur. Recent years have seen resurgence in communities with low vaccination rates, including notable outbreaks in 2019 and 2024-2025.
Globally, measles remains a leading cause of vaccine-preventable death. The WHO estimates that in 2022, there were 136,000 measles deaths worldwide, mostly among children under 5 years old (WHO, 2024).
In 2019, the U.S. experienced 1,282 individual measles cases across 31 states - the largest number since 1992. This was largely driven by outbreaks in under-vaccinated communities. In 2024, new outbreaks have been reported in multiple states (CDC, 2024).
Most measles cases in the U.S. occur among unvaccinated individuals who traveled to areas with ongoing transmission and brought the virus back to their communities. The virus spreads quickly in settings with low vaccination rates, such as schools and daycare centers.