It should not have happened, and yet it did. We know better, but we continue to make the same mistakes. Measles (rubeola), the most contagious virus infecting humans (FIGURE 1), remains endemic in many parts of the world. Thanks to highly effective measles, mumps, and rubella (MMR) vaccines, the virus was declared eliminated in the US in 2000.1 Yet, as of August, more than 1300 US cases have been reported in 2025,1 with larger outbreaks in Ontario, Canada, and Chihuahua, Mexico.2 Most of the US cases (~ 96%) involve unvaccinated children and young adults—and at least 3 have died. The rise in cases from 2024 highlights the growing threat of declining vaccination rates, travel, and community spread in undervaccinated populations.
There are many drivers for this situation, including:
• questioning the need for ongoing vaccination (among the public and some government officials and health care professionals);
• ongoing circulation of misinformation and disinformation about the safety and effectiveness of vaccination (writ large);
• mistrust of public health authorities; and
• vaccine fatigue emerging from the COVID-19 pandemic.