Tracking the drop in U.S. childhood vaccinations: Our methodology

Editor’s note: This 2026 NBC News data investigation is an update of The Vaccine Divide, which was originally published in September 2025. The methodology for both projects is similar. The new data was collected from June to October 2026.

For “The Vaccine Divide,” NBC News gathered massive amounts of data from state governments and archives of public records. With the help of infectious disease researchers at Stanford University, NBC News filed scores of requests for documents, including materials obtained under the Freedom of Information Act, and wrestled different types of data into a standardized format to map and compare rates across thousands of counties.

NBC News built a database of childhood vaccination and exemption information using data provided by state governments, primarily health agencies. The data combines public information available for some states and data provided directly to NBC News.

The data covers kindergartner vaccinations for each academic year.

After collection, the data was collated, and exemption rates were calculated in order to be analyzed. The analysis focuses on four facets of the data:

With a hodgepodge of formats, jurisdictions and collection practices across states, the task required extensive work to ensure that possible inconsistencies in the data were managed.

Original source: https://www.nbcnews.com/health