Colorado Measles Outbreak Grows to 10 Cases as Broomfield Spread Continues

On a late February afternoon, an unvaccinated teenager at Broomfield High School went about a normal school day — attending classes, moving through hallways, likely unaware that the measles virus was already replicating in their body. Days later, when symptoms finally appeared, the damage was done. The virus had already been shed into the air of a school serving 1,500 students, and the clock on Colorado's first measles outbreak of 2026 had begun ticking.

By March 12, that single case had ballooned to 10 — two newly confirmed infections and one probable case announced alongside seven prior cases, all linked to the outbreak that began at Broomfield High School and quickly spread to nearby Broomfield Heights Middle School [1][2]. Every confirmed case has been in an unvaccinated person between the ages of 5 and 17, and the geographic footprint now stretches across four Colorado counties: Adams, Arapahoe, Broomfield, and Weld [3].

The outbreak offers a street-level view of what public health officials have been warning about for years: as vaccination rates slip below critical thresholds, even communities with high overall immunization can become kindling for a highly contagious disease that was eliminated from the United States a quarter century ago.

The Broomfield Outbreak: A Timeline of Spread

The first confirmed case was reported in late February 2026, tied to a student at Broomfield High School. A second case quickly followed at the same school, prompting health officials to begin contact tracing and identify potential exposure locations [4]. On March 4, when a third connected case was confirmed, the Colorado Department of Public Health and Environment (CDPHE) officially declared an outbreak — the technical designation triggered when three or more related cases are identified [5].

What followed was a rapid cascade. Four additional cases were announced on March 6, bringing the total to seven. Among the new exposure sites: Denver International Airport, where an infectious individual had been present on February 16 between 6 and 9 p.m. [6]. By March 10, the count stood at nine, with exposures reported at a bowling alley, multiple restaurants, healthcare facilities, a church, and a grocery store across Broomfield, Westminster, Frederick, Lafayette, Louisville, and Denver [7].

The latest cases, announced March 12, brought the total to 10. Two of the new infections occurred in household contacts of previously confirmed cases — people living in the same home as an infected child who were themselves unvaccinated [1]. One additional probable case, potentially representing a breakthrough infection in a vaccinated individual, was still under investigation [8].

In total, health officials have identified at least 21 possible exposure locations linked to the outbreak [8].

80 Students Sent Home — For Weeks

One of the most immediate consequences has been the exclusion of approximately 80 unvaccinated students and staff from Broomfield High School and Broomfield Heights Middle School [9][10]. Under Colorado state statute, public health officials have the authority to exclude unvaccinated individuals — including those with personal or religious exemptions — from school settings during an outbreak of a vaccine-preventable disease.

The exclusion period is not a simple three-week countdown. It resets with each new case. As a CDPHE spokesperson explained: "It is not a countdown from the first case; it is a countdown from the last known exposure at the school" [6]. For families of excluded students, this creates an indefinite educational disruption that grows longer with each new infection.

The irony is sharp: Broomfield High School has a 97% vaccination rate for the MMR (measles, mumps, and rubella) vaccine. Broomfield Heights Middle School stands at 96.7% [6]. Both figures exceed the 95% threshold generally considered necessary for herd immunity. Yet the small fraction of unvaccinated students proved sufficient to sustain a chain of transmission, particularly given measles' extraordinary contagiousness — one infected person can transmit the virus to 12 to 18 others in an unprotected population.

Colorado's Eroding Immunity

The Broomfield schools may be above average, but Colorado's statewide picture is far less reassuring. Only 91% of the state's kindergartners have received at least one dose of the MMR vaccine — well below the 95% herd immunity threshold [11]. Among kindergartners specifically, MMR coverage was just 88% during the most recent school year, with polio coverage at 87.6% and DTaP at 87.4% [12].

Source: CDC Measles Cases and Outbreaks

Data as of Mar 12, 2026CSV

The trend has been moving in the wrong direction. Colorado's childhood immunization rates have fallen below 90% for two consecutive years, and the state is one of only 15 that allows personal belief exemptions — known as Non-Medical Exemptions (NMEs) — for school vaccination requirements [12]. Personal exemptions among kindergartners have risen to 4.2%, and the state's process for obtaining an exemption remains among the easiest in the country [12].

Until 2025, Colorado had not recorded more than two measles cases in a single year since 1996 [3]. Then came 36 cases across the state in 2025. Now, barely two and a half months into 2026, the count has already reached 10 — a pace that suggests Colorado's three-decade stretch of effective herd immunity may be over [11].

A National Crisis in Miniature

Colorado's outbreak is a microcosm of a much larger national emergency. As of March 12, 2026, the CDC has confirmed 1,362 measles cases across the United States since the start of the year — with 94% of those cases (1,281 of 1,362) associated with outbreaks [13]. The nation is on pace to far exceed the 2,284 cases recorded in all of 2025, which itself represented a 34-year high [14].

Source: GDELT Project

Data as of Mar 14, 2026CSV

The epicenter of the national surge has been South Carolina, which has confirmed more than 847 cases since October 2025, with infections spreading across state lines into North Carolina and Washington [15]. Texas has also been hit hard. Three deaths have been confirmed nationally — two unvaccinated children in Texas and one unvaccinated adult in New Mexico [13].

Across the full outbreak period from January 2025 through March 2026, approximately 93% of cases have occurred in people who were unvaccinated or whose vaccination status was unknown [13]. The pattern is consistent and unambiguous: measles is a disease of the unvaccinated.

The Elimination Status Question

Perhaps the most consequential dimension of the crisis is what it means for America's measles elimination status. The United States was declared measles-free by the Pan American Health Organization (PAHO) in 2000, after demonstrating no sustained domestic transmission for 12 months. That status — a hard-won public health achievement — is now in jeopardy [15].

In November 2025, the broader Region of the Americas, including Canada, lost its regional measles elimination designation after endemic transmission persisted for more than 12 months [16]. The United States and Mexico face individual review, originally scheduled for April 2026 but now delayed to November 2026 [17].

Some public health experts believe the question is already settled. Dr. Demetre Daskalakis, a former CDC official, has stated bluntly: "We do not have the capability to actually control measles...elimination is already lost" [15]. The assessment reflects a growing consensus that the U.S. is no longer able to consistently interrupt measles transmission chains before they establish themselves in communities.

Losing elimination status would carry both practical and symbolic consequences. It would signal to the world that the wealthiest nation on earth has allowed a vaccine-preventable disease to re-establish itself — a failure that public health researchers estimate costs approximately $43,000 per case, with large outbreaks exceeding $1 million in total expenditures [15].

The Vaccination Gap: Why It's Widening

National MMR vaccination coverage among kindergartners has slipped from 95.2% during the 2019-2020 school year to 92.5% during the 2024-2025 school year [18]. While 92.5% may sound high, for a disease as contagious as measles, every percentage point below the 95% threshold matters enormously.

Source: GDELT Project

Data as of Mar 14, 2026CSV

The reasons for the decline are multifaceted. Vaccine hesitancy — fueled in part by misinformation on social media — has grown since the COVID-19 pandemic. Some parents conflate COVID-19 vaccine debates with longstanding childhood immunizations that have decades of safety data behind them. Others cite personal or religious beliefs.

In Colorado specifically, the ease of obtaining a Non-Medical Exemption has been identified as a contributing factor. Though the state implemented a new exemption process intended to require more deliberation, health officials acknowledge the bar remains low compared to states that only allow medical exemptions [12].

The consequences play out in predictable ways. Higher rates of non-medical exemptions have been statistically linked to increased disease transmission [12]. And in a school like Broomfield High, where the 3% of unvaccinated students were enough to fuel an outbreak, the mathematics of herd immunity become tangible.

What Happens Next in Broomfield

The immediate future depends on whether new cases continue to emerge. Each new infection resets the 21-day exclusion clock for unvaccinated students, potentially keeping them out of school for weeks or months. Parents of younger children have begun seeking early MMR vaccination — the shot is typically given at 12-15 months and again at 4-6 years, but can be administered as early as 6 months in outbreak situations [19].

Health officials continue to urge anyone who may have been exposed to monitor for symptoms for 21 days and to contact their healthcare provider before visiting a medical facility if symptoms develop. The MMR vaccine can still provide protection if administered within 72 hours of exposure [8].

For the 80 excluded students and their families, the outbreak has already upended daily life. For the broader Broomfield community — and for Colorado — it serves as an urgent case study in what happens when vaccination rates dip below the threshold that once kept measles at bay for three decades.

The Bigger Picture

The Broomfield outbreak, while modest in absolute numbers compared to South Carolina's hundreds of cases, carries outsized significance. It demonstrates that measles can gain a foothold even in schools with vaccination rates above 95%, as long as unvaccinated individuals cluster and the virus finds its way in. It shows how quickly a single case can ripple across four counties and 21 exposure sites. And it illustrates the cascading disruptions — school exclusions, contact tracing across an entire metro area, public anxiety — that accompany even a contained outbreak.

Colorado's experience mirrors a national pattern: years of gradually declining vaccination rates, enabled by permissive exemption policies and growing vaccine hesitancy, have created the conditions for a disease that was once eliminated to return with force. The 10 cases in Broomfield are not an anomaly. They are the predictable result of a slow erosion that public health officials warned about long before the first teenager at Broomfield High School developed a rash.