The largest US measles outbreak in over 25 years is unfolding, exposing a complex dynamic between risk, hesitancy and vaccination. Organizations everywhere can learn much from it.
Nestled between the bigger cities of Charlotte and Greenville, Spartanburg County is home to 400,000 South Carolinians. Here, BMW operates its largest production facility, employing 11,000 people amidst a multi-billion-dollar upgrade. Over the past 20 years, household incomes and educational outcomes have risen steadily. But Spartanburg has also mirrored a quieter national trend: declining vaccination rates that have reopened the door to diseases once considered eliminated.
In early October, the first measles cases appeared. In December, the county experienced a holiday surge, where church and school exposures drove the cases upward. By January, there was explosive growth: 185 cases reported on January 2nd. Over 500 cases by mid-January. By the end of the month, it exceeded 800 — making it the largest measles outbreak in the United States since the disease was declared eliminated in 2000. The outbreak spread across county lines and into neighbouring states. At the end of January, at least 15 states had reported measles cases, many of which were linked to the South Carolina cluster.
Spartanburg’s vaccination rate is below what is needed for herd immunity. But what made Spartanburg vulnerable is shared widely. Thirty-nine of America’s 50 states are below the herd immunity threshold. Countries around the globe are losing their measles vaccination status. But a growing body of recent research is clarifying not just where the risks are concentrated, but where the greatest opportunities for effective response lie.
The Coverage Picture
US measles vaccination has been quietly eroding for over a decade. Coverage sat near 95% through the 2010s. It spent the decade hovering just above the WHO recommendation for herd immunity. The pandemic accelerated the decline sharply, and it has not reversed. By 2024–25, national kindergarten MMR coverage had dropped to 92.5%. Non-medical exemptions have nearly tripled since 2011. CDC surveillance data underscores the link between vaccination and outbreaks: 93–95% of new measles cases in 2025 occurred in completely unvaccinated individuals. Roughly one quarter of cases are in children under 5 years old, some of whom are too young to receive a vaccine.
There is also a persistent gap between first and second doses. MMR Dose 1 rates run 5–10% higher than Dose 2, which is scheduled at age four to six (recommended before starting school). The drop-off is typically attributed to scheduling difficulty — parents who vaccinated once but did not return for the follow-up — rather than refusal. But the sharper danger is the growing number of children in the US with no protection at all. An analysis of over 320,000 electronic health records, published in JAMA Network Open in January 2026, found that between 2020 to 2024, the share of children reaching age two with zero MMR doses has climbed from 5.3% to 7.7%.
"It's not that bad"
One recurring theme in the literature on vaccine hesitancy is the belief that measles is a minor illness — a “forgotten disease” that does not justify the perceived risks of vaccination. The clinical data says otherwise. In 2025, about one in eight US measles patients required hospitalization — rising to nearly a quarter for children under five. Measles in infancy and childhood often leads to immune amnesia, or the depletion of immune memory to other pathogens, which can last up to 5 years. And infections can be fatal in about 1 in 1,000 cases in high-income settings. The seriousness of this disease in infants is one of the reasons why herd immunity is so important, in that it protects those among us who are the most vulnerable.
On a per-case basis, measles puts a huge burden on the operational resiliency of an organization. Patient absenteeism runs 10–14 days. Caregiver absenteeism — parents staying home with sick children — averages 9–15 lost workdays per case. These are exceptionally prolonged absences compared to most common diseases. A 2025 Johns Hopkins systematic review of US measles outbreaks found the average total cost per case was $43,203, nearly half driven by productivity loss. School and work absences during outbreaks run roughly ten times higher than actual case counts — a product of 21-day quarantine protocols for unvaccinated contacts.
On our radar (spotlight on Measles)
While much attention has been paid to the growing situation in the United States, our reporting shows there are several concerning outbreaks across the globe.
Measles in South and Central America
A sustained increase in measles cases has been reported in the Region of the Americas in 2025 compared to recent years; a trend that has continued into 2026. Several countries entered 2026 with active outbreaks: As of mid-Feb 2026, eight countries had reported a case within the previous 42 days, indicating ongoing outbreak activity (Costa Rica, Argentina, Guatemala, Chile, Peru, Uruguay, Honduras, El Salvador). Low vaccination coverage, paired with population mobility, may contribute to rapid outbreak amplification, as demonstrated in Guatemala following a mass gathering that was held between 10-14 December 2025 that has since resulted in sustained local transmission and travel-associated cases in nearby regions.
We recently conducted a deep dive Intelligence Report on the situation in South and Central America. Outbreak Insider readers may contact us to read the report.
Other Measles Outbreaks in Early 2026
In January and February of this year, we have reported on concerning outbreaks in multiple areas of the globe.
In the MENA region, Yemen and Israel both reported significant outbreaks. In Yemen, a sharp spike of cases comes paired with the concerning likelihood of significant underreporting. Israel experienced clusters of cases across the country, with most cases being reported in Jerusalem. Somalia and Sudan have also been experiencing large outbreaks. In Sub-Saharan Africa, the DRC and Angola reported continued significant activity of measles. In both instances, these events were carried over the prior year.
While Europe has not yet had an outbreak that rose to our notable event criteria, it is worth noting that 2025 saw notable outbreaks in France, Spain, Italy, the Netherlands and the United Kingdom. In early February, 3 European countries were among the 6 that lost measles elimination status, a foreboding sign for 2026. The BlueDot team continues to monitor activity on the continent carefully.
Lastly, Mexico is reporting its worst outbreak in over 20 years. Cases have been reported in every state in the country. The outbreak originated from a cluster in Texas, and Chihuahua, a state bordering Texas and New Mexico, is reporting the highest burden of cases in the country.
In the past 12 months alone, BlueDot has issued 106 alerts for notable measles outbreaks. When paired with our personalization engine and information on travel connectivity, clients are offered prioritized, timely updates on all disease threats relevant to their operations and communities.
The US Risk Map
National and state-level vaccination statistics create a misleading picture of measles vulnerability. At the state level, the gap is already stark: Idaho’s kindergarten coverage is below 79%; Connecticut’s is above 98%. But the real risk is concentrated in pockets that even state-level data obscure.
A January 2026 study in Nature Health surveyed 22,062 parents of children under five to generate county-level MMR coverage estimates across the United States. The results were sharply different from official figures. The median county-level coverage was just 71% — and ranged from as low as 36% to a high of 87%, well short of the 95% threshold. The gap partly reflects who the study captures: official data relies on school-entry records, which miss homeschooled and uninsured children — populations that participatory surveillance is designed to reach.
The study identified clusters of low coverage — hot spots — in West Texas, southern New Mexico, parts of Mississippi, and across the rural Southeast. Low-coverage areas clustered together geographically, creating contiguous zones of vulnerability. Where clustering was present, measles cases were more than twice as likely.
South Carolina’s county-level data broadly supports this picture. Not a single county in the state reached 80% coverage in the study’s estimates. Twenty-six of the state’s 46 counties were classified as low-coverage clusters — low-coverage counties surrounded by other low-coverage counties. The data was collected before the outbreak began.
But Spartanburg County — where the outbreak ignited — was not one of them. At just under 75%, it was among the state’s better-covered counties — and not flagged as a cluster. The outbreak started there anyway. Coverage 20 points below herd immunity is dangerous whether or not the county next door is worse. Clustering indicates areas of risk, but any community with insufficient vaccine coverage is susceptible to outbreaks.
Why Coverage is Falling
Vaccine coverage and vaccine hesitancy is a well-studied topic, but the COVID-19 pandemic has, in some cases, worsened sharp societal shifts on the topic. Recent research offers clues into what has, and hasn’t changed. It also offers some important guidance on ways to combat the trend of downward vaccine adoption.
Who refuses — and why
Active refusal — parents who deliberately opt out of vaccination — represents 2–3.6% of the population nationally. But this group clusters geographically, creating localized pockets where herd immunity collapses.
A July 2025 study in JAMA Network Open surveyed 174 pregnant individuals and 1,765 parents of children aged zero to five. Among parents with existing children, more than one in five intended to refuse all vaccines — a dramatic jump from under 2% among first-time expectant parents. The most common reasons: a preference for natural immunity, concerns about vaccine ingredients, and discomfort with multiple shots at a single visit.
The strongest predictor of refusal was a negative prior experience — a perceived side effect that the parent felt was not adequately explained by their paediatrician. Refusal was higher among parents who felt their concerns had been dismissed.
A window that closes
The same study revealed a striking pattern. Among first-time pregnant women, nearly half described themselves as uncertain about their child’s future vaccinations. Their concerns closely mirrored those of active refusers — long-term safety, multiple shots at one visit, contradictory information online — but their positions had not yet hardened.
But among parents who already had children, uncertainty dropped to 3.5% from nearly 50%. Parents move from undecided to decided, and the decision increasingly skews toward refusal. First-time parents are reachable — their concerns are specific and addressable. But the window is narrow, and once it closes, opinions become much stronger.
The clinical record supports this. The JAMA Network Open analysis of children’s health records found that those with regular healthcare access who missed their two-month or four-month routine appointments were significantly more likely to never receive the MMR at all. Early disengagement from the healthcare system — whether from hesitancy or logistics — compounds over time.
The practical gap
Not all under vaccination is ideological. A 2022 analysis of National Immunization Survey data found that parental hesitancy accounts for about 25% of undervaccination in children. The remaining 75% is driven largely by structural barriers: lack of insurance, transportation, inability to take time off work, and clinic logistics. Parents also overestimate their child’s vaccination status by about 10–15% — the missing shots are typically not the result of a deliberate decision, but of a schedule that fell behind. Children without a consistent primary care provider are 15% more likely to be behind on their MMR series, regardless of their parents’ beliefs about vaccines.
Who is trusted
Public support for school vaccination requirements has dropped from 82% in 2019 to 69% in late 2025. Trust in the CDC and pharmaceutical companies has eroded across the political spectrum. But the data also reveals where effective engagement is still possible — and who is best positioned to deliver it.
Personal healthcare providers remain the most trusted source of vaccine information — even among hesitant and refusing parents. On a five-point scale, parents rated trust in their personal provider at 3.8 — nearly double the CDC and more than double pharmaceutical companies. This gap appeared consistently across the data, including among parents who intend to refuse vaccination entirely.
Research supports what makes provider communication effective. A 2024 study in the Journal of Health Communication found that storytelling and personal anecdotes were significantly more persuasive than statistical posts or expert-driven data for vaccine-hesitant parents. Personal narratives outweigh institutional data for the undecided group. The format matters as much as the messenger.
But the clinicians need support. A December 2025 Leger study found that only 40% of frontline healthcare workers feel confident addressing vaccine hesitancy with patients. The pathway is clear: trusted providers, narrative communication, targeted engagement with first-time parents. Actively equipping clinical teams with timely, accurate, and compelling information is the single highest-leverage investment in vaccination uptake.
BlueDot enables in-depth support to clinicians.
BlueDot works closely with Public Health of all types, including those who are tasked with supporting clinical networks with accurate, digestible and timely updates on infectious disease risk.
Contact us to learn more.
Key Takeaways
- Measles is more severe than the popular imagination suggests: Measles has a 13% hospitalization rate (and nearly 25% for those under five), illnesses that require weeks of absenteeism on average, and quarantine protocols that produce ten times more absences than actual infections. The perception that measles is a minor childhood illness persists — and it undermines urgency at every level.
- Know the hot spots in your area — but know that outbreaks don’t only start there: County-level data reveals sharp geographic variation in coverage, with clustering that doubles the likelihood of outbreaks. But Spartanburg was among South Carolina’s higher-coverage counties and still became the epicentre of the largest US outbreak in over 25 years. Risk exists well beyond the identified hot spots.
- First-time parents are the key engagement window: Nearly half of first-time expectant parents are uncertain about vaccination. After the first child, positions harden — and the share intending to refuse jumps from under 2% to over 22%. The window for effective engagement is narrow and early.
- Clinicians are the most trusted messengers — and they need support: Provider trust scores nearly double the CDC’s, even among hesitant parents. Narrative communication outperforms data-driven messaging. But only 40% of frontline healthcare workers feel confident addressing vaccine hesitancy, citing misinformation fatigue. Supporting clinical networks with timely, accurate, and compelling information is the most direct path to reaching the populations that matter most.
BlueDot works with leading organizations in public health, life science, along with enterprise risk management and occupational health and safety teams across the private sector. We detect, triage and advise on infectious disease threats worldwide, empowering our clients to take effective action in the face of infectious disease. If you would like to learn more about our intelligence and services, please get in touch.
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