Tracking County-Level Measles Cases in the US

Prior to the introduction of the measles vaccine, more than 90% of US residents were infected with the measles virus before the age of 15 years, with the 3 million to 4 million annual cases of measles resulting in approximately 48 000 hospitalizations. After the licensure of the first measles vaccine in 1963, national efforts to terminate indigenous measles transmission in the US through increased vaccination coverage in school-aged children, alongside surveillance and outbreak control, led to the elimination of endemic measles in 2000. From 2000 to 2024, annual measles cases in the US averaged less than 200. However, in 2025, more measles cases have already been reported than any year in more than 3 decades, with 1356 cases confirmed as of August 12, 2025, across 42 jurisdictions. The surge in measles cases since 2020 also coincides with declining vaccination coverage in the US, further increasing the risk of measles outbreaks and threatening the US' current endemic elimination status.

US measles surveillance data have historically been provided by the US Centers for Disease Control and Prevention (CDC), which publishes confirmed measles cases at the national and state levels on a weekly basis. However, measles outbreaks are often highly localized and can only be meaningfully captured with more granular data. To address this surveillance gap, the study investigators developed a national data collection and reporting infrastructure that provides near-real-time, county-level measles case data beginning on January 1, 2025, shared via a public dashboard and open data repository.