Behind the data: How rising school exemptions are threatening public health

This year’s lethal spread of measles in rural West Texas^[1] and other pockets of the U.S. was a strong warning about how protection against deadly childhood diseases is eroding around the nation.

This was a key conclusion of a six-month NBC News investigation, in collaboration with Stanford University, resulting in the most comprehensive analysis of vaccinations and school exemptions to date.

NBC News gathered massive amounts of data from state governments and archives of public records reaching back years or decades. With the help of infectious disease researchers at Stanford, 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.

The analysis found that a large swath of the U.S. currently does not have the basic, ground-level immunity medical experts believe is necessary to stop the spread of measles, which had once receded into the past.

The idea for this project originated from a conversation about how to cover changes in vaccine policy and opinion between the NBC News Health and Medical unit and Dr. Peter Hotez, a vaccine expert and dean of the National School of Tropical Medicine at Baylor College of Medicine in Dallas.

The conversation led to infectious diseases scientist Dr. Nathan Lo at Stanford University, who had mapped out vaccination and exemption data in a few states. Lo became a collaborator in this monthslong data project, helping identify the limitations of the broader state-level vaccination trends that are collected by the Centers for Disease Control and Prevention.

Outbreaks start locally

We put vaccination trends under a microscope, down to the county level. The findings could help public health officials better predict where the next outbreak may occur and how to best allocate resources to stop it.

Or parents of children at high risk of complications from infectious diseases could find out if their community is a potential hot spot.

The analysis has identified unexpected trends.

For example, St. Louis, a diverse, major metropolitan area, is in the midst of a slide in immunization rates. That’s why it is a reporting focus.

These findings uncover a fracture in an already fragmented society: The vaccine divide.

Our Methodology

How NBC News collected the data

NBC News built a database of kindergarten vaccination and exemption information using data provided by state governments, primarily health agencies^[2]. 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:

1. Medical exemptions: Exemptions granted when students have a medical condition that would make vaccination potentially harmful.
2. Nonmedical exemptions: Exemptions for students who opt out of required vaccinations due to personal beliefs or religious convictions.
3. MMR (measles-mumps-rubella) vaccinations: For states in which data is subdivided by number of doses, MMR vaccination is counted by the second dose.
4. Up-to-date vaccinations: Students are considered “up-to-date” with their vaccinations if they have received the full vaccination series required for enrollment in their school.

How the data was processed

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.

• Certain states, such as Ohio and New York, required further calculations to aggregate the state-supplied data.
• Other states required hand input of hundreds of rows of tabular data.
• All data was checked for accuracy.

Analyzing the data

Each state collects its data differently. Some use health districts instead of counties. Some states provided over a decade of data, others only two years. Some states redacted certain data due to privacy concerns.

• Not all states have recent data. Florida did not provide data on kindergarten exemptions after the 2021-2022 school year. Montana stopped collecting vaccine and exemption data after 2019, first due to Covid and thereafter due to the passage of a state bill (HB 334^[3]) in 2021 that struck down the mandate for the state to collect data on immunizations.
• Certain states (such as Arizona, Colorado and Minnesota) do not collect an overall “up-to-date” figure representing the percentage of kindergarteners who are compliant with all required vaccines. Others (such as Florida, New Hampshire, New Jersey and South Carolina) provided only “up-to-date” numbers.
• In other states — Mississippi, New Hampshire and South Carolina — data was provided only for years K-12, rather than specifically kindergarteners. West Virginia also falls into this category for their exemption data. Mississippi could share only pre-K-12 exemption data.
• Some states — Illinois and New York — do not collect data at grade level, so data is for elementary schools as a whole (up to K-8 for Illinois, New York was based on New York State Education Department labeling of elementary schools), rather than kindergarteners in specific. Hawaii also fell into this category (up to K-5), as its school-level data was more consistent than its kindergarten-specific data. New Mexico includes 5- and 6-year-olds in its data, and state officials told NBC News that the inclusion of children before they enter kindergarten is one reason its vaccination rates are lower than in other places.
• Other states did not provide data on a county level. Alaska, Kansas and Nebraska provided data for other jurisdictions. Delaware and Rhode Island provided only state-level figures. Indiana was unable to provide county-level exemption data. West Virginia was unable to provide county-level immunization data.
• Some states (e.g., Michigan, New Mexico) collect data by calendar year, rather than school year.
• Wyoming did not consistently report data among kindergarteners, so the most consistent reported value was used instead: one-dose MMR among 19- to 35-month-olds. Accordingly, exemptions among children younger than 5 were used to correspond with this age group.
• West Virginia was unable to provide county-level immunization data, but was able to provide exemption data per county, starting with the issuance of Executive Order 7-25 in January, which overturned the state’s longstanding ban on nonmedical exemptions.
• Alaska was unable to provide regional exemption data for privacy reasons because of small sample sizes.