PHOENIX — Childhood immunization rates for measles and mumps have decreased significantly across Arizona in recent years, plunging the state further below the threshold that public health officials say is needed to achieve "herd immunity."

Data compiled by NBC News in partnership with Stanford University shows that 77% of the country's counties and jurisdictions have reported a decline in MMR vaccination rates since 2019 and most Arizona counties are no exception.

Arizona's statewide MMR immunization rate dropped from 93.5% to 88.7% between 2019 and 2024. The "ideal" threshold to attain herd immunity and avoid disease outbreaks is 95%, according to messaging from the Arizona Department of Health Services.

The state health department did not respond to inquiries asking how Arizona is re

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