Understanding the Decline in U.S. Childhood Vaccinations

A recent investigation has shed light on the significant decline in childhood vaccination rates across the United States, with particular emphasis on the MMR (measles, mumps, rubella) vaccine. This report is based on data collected between June and October 2026 and seeks to understand the factors contributing to these troubling trends.

Data Collection Overview

The study compiles extensive vaccination data sourced from various state health agencies and public records. By employing the assistance of infectious disease researchers from Stanford University, the project accessed numerous documents, many obtained through the Freedom of Information Act. This effort allowed for the creation of a standardized database, making it easier to evaluate vaccination rates across thousands of counties.

Components of the Analysis

The analysis focused on four key areas concerning childhood vaccinations:

• Medical Exemptions: These are granted to children for medical reasons that could make vaccination harmful.
• Nonmedical Exemptions: These exemptions reflect personal beliefs or religious convictions that lead families to opt-out from vaccinations.
• MMR Vaccinations: MMR vaccination rates include data on the second dose and use measles immunization rates in states that do not differentiate between MMR components.
• Up-to-date Vaccination Status: A child is considered up-to-date if they have received all required vaccinations for school enrollment.

Data Processing Challenges

Given the diversity of data collection methods and formats across the states, processing the data was no easy task. Some states, like Ohio and New York, required additional calculations to accurately aggregate their vaccination information, while others demanded manual entry of extensive tabular data. Each data point underwent rigorous verification to ensure accuracy.

The analysis specifically concentrated on states that provided MMR vaccination figures for the 2025-2026 academic year. Multiple variant analyses were performed to confirm the reliability of the results, with findings consistently showing a decline in vaccination rates across the board.

Vaccination Rate Trends

Almost 40% of counties noted a decrease of over 5 percentage points in MMR vaccination rates since 2019, while around 12% experienced similar declines since 2024. Notably, less than 2% of counties reported a marginal decline of 0.1 percentage points or less since 2019.

The report illustrates significant variations due to differences in state data collection practices. Some states rely on health districts rather than counties, and the availability of data varies greatly. For instance, Florida ceased reporting kindergarten exemption data after the 2021-2022 school year, and Montana stopped collecting vaccination information altogether following changes in state law.

Inconsistencies and Variations

Many states provide varying lengths of data records, with some offering over a decade's worth while others might only have two years available. Privacy concerns have also led to certain data being redacted in specific states, complicating efforts to make comprehensive comparisons.

Several states, including Arizona and Minnesota, do not report the percentage of kindergarteners who are up-to-date with vaccinations. Others, like Mississippi and South Carolina, provide data only for K-12 populations rather than focusing specifically on kindergartners.

To further complicate matters, some states collect data based on the calendar year instead of the school year. Wyoming's reporting on kindergartener vaccination data has also faced inconsistency, leading to reliance on alternative age groups for MMR assessment, particularly focusing on children aged 19 to 35 months.

Overall, while the investigation reveals critical trends in childhood vaccinations, it also highlights the significant challenges presented by the varying collection and reporting practices of different states. Addressing these inconsistencies will be essential in any efforts to improve vaccination rates and public health outcomes.