Colorado measles vaccination rates are falling behind other states, leading to a lower herd immunity among children.

A recent data analysis by The Washington Post found that Colorado has an 88% herd immunity status regarding the measles-mumps-rubella (MMR) vaccine between 2023 and 2024 — well below the 95% threshold set by doctors across the country.

Ultimately, 95% or more of kindergartners should be vaccinated against measles to achieve overall protection for the class — or “herd immunity.”

Only seven of Colorado’s 64 counties met the herd immunity threshold in 2023 or 2024 (depending on available data). All are in the southern part of the state, including Mineral County and San Juan County.

Denver County, for example, had an 89% vaccination rate in 2023-2024. Douglas and Adams counties were the highest in the metro area with 92% — still below the herd immunity threshold.

Nearby states — New Mexico, Kansas and Nebraska — all have vaccination rates in the 90s, with New Mexico passing the herd immunity threshold with 95%.

Colorado is no outlier, though.

According to the data, at least 5.2 million kindergarten-age children in the country are living in counties where vaccination rates for classrooms have fallen below the herd immunity threshold — up from about 3.5 million before the 2020 COVID pandemic.

Colorado had 36 measles cases in 2025. The state has only had zero or one case each year since 2014 (with two in 2016).

According to the Colorado Department of Public Health and Environment (CDPHE), 28 of the cases were in those who were unvaccinated or have unknown vaccine status.

The Washington Post’s report came just a week before the U.S. Centers for Disease Control and Prevention (CDC) changed its children’s vaccine recommendation from 18 diseases to 11.

The MMR vaccine remains on the CDC’s “recommended for all” list, though, and the changes will not affect insurance coverage or vaccine availability through the federal Vaccines for Children program. 

CDPHE will continue to recommend the vaccines previously on the list to Colorado children, according to a Tuesday news release. The school and child care immunization requirements have not changed, either.

“Vaccines have an exceptional safety record and remain one of the most effective tools we have to prevent serious disease,” said Dr. Rachel Herlihy, deputy chief medical officer at CDPHE. “Colorado will continue to follow expert guidance that reflects the best available science and supports informed decision-making between families and their health care providers, as always.”