A significant decline in measles-mumps-rubella (MMR) vaccination rates among children has been observed across the United States following the COVID-19 pandemic, raising concerns about potential outbreaks of preventable diseases. The findings come from a new research letter published online on June 2 in the Journal of the American Medical Association (JAMA).

Led by Dr. Ensheng Dong of Johns Hopkins University, the study compiled a comprehensive dataset detailing annual county-level MMR vaccination rates for children from 2017 to 2024, covering 2,237 counties across 38 states. The data revealed a clear downward trend in vaccination coverage, particularly during and after the pandemic.

According to the analysis, the average county-level MMR vaccination rate fell from 93.92% before the pandemic to 91.26% afterward across 2,066 counties in 33 states. This represents a mean decline of 2.67 percentage points—a potentially critical drop in a country where public health relies on high levels of immunization to maintain herd immunity.

The researchers noted significant regional disparities, with some states and counties experiencing much steeper declines than others. Alarmingly, 78% of the counties analyzed reported a drop in vaccination coverage. Only four states showed an increase in median county-level MMR vaccination rates during the same period.

"This widespread decline in childhood MMR vaccination is concerning," the authors wrote, noting that even a small reduction in immunization coverage could lead to resurgences of highly contagious diseases like measles, which requires at least 95% coverage to prevent outbreaks.

Experts suggest that pandemic-related disruptions—such as limited access to healthcare services, vaccine misinformation, and parental hesitancy—may have contributed to the decline in routine childhood immunizations. As the nation continues to recover from COVID-19, health authorities are urging parents and healthcare providers to prioritize catch-up vaccinations.

Public health officials warn that reversing this trend will require targeted outreach, education, and policy support to ensure that children across all regions of the U.S. are protected against these dangerous but preventable diseases.