Modeling and Characterizing the Growth of the Texas-New Mexico Measles Outbreak of 2025.

BACKGROUND: In late January 2025, a measles outbreak began in Gaines County, Texas, USA, and the outbreak extended to New Mexico. We used a variety of mathematical models to estimate the growth rate of the Texas-New Mexico measles outbreak of 2025. METHODS: We used both empirical and mechanistic models based on differential equations to make the estimations that allow us to characterize this measles outbreak. Regarding empirical models, we used the exponential growth model to compute and estimate the growth rate, basic reproduction number, R0, and effective reproduction number Rt. With regard to mechanistic models, we use the SIR and SEIR models to estimate the growth rate, basic reproduction number R0, and effective reproduction number Rt. We used new weekly measles cases and also cumulative cases. RESULTS: Using the exponential growth model, we estimated a basic reproduction number between 32 and 40. For the classical SIR model, we estimated that the basic reproduction number is approximately 30. CONCLUSION: We found that the current Texas-New Mexico measles outbreak of 2025 has a slightly higher growth rate and effective reproduction number Rt compared to several previous measles outbreaks around the world.