Measles outbreak in southwestern Wisconsin grows to 159 cases as school year begins

A measles outbreak that took hold in three rural counties in southwestern Wisconsin late this summer has grown to 159 confirmed and probable cases statewide, making it one of the largest state-level outbreaks recorded during a year in which the United States as a whole is already tracking record measles activity. State health officials say transmission is continuing inside the community and have used the start of the school year to press parents to check their children's vaccination records.

The Wisconsin Department of Health Services said the tri-county outbreak, centered on Grant, Iowa and Lafayette counties, stood at 151 confirmed cases and six probable cases as of September 8, according to the agency's outbreak tracking page. Combined with unrelated cases reported earlier in the year, the state's 2026 measles total reached 159. Local television stations in the region, including WBAY in Green Bay and KCRG in Cedar Rapids, which covers the Iowa side of the outbreak region, have tracked the case count climbing nearly every few days since mid-August.

The numbers behind the outbreak

Of the 159 statewide cases, 158 were in people who were unvaccinated against measles, according to the health department. Lafayette County has recorded the most cases, with 77 confirmed or probable, followed by Iowa County with 62 and Grant County with 18. Roughly half of the cases are in children between the ages of 5 and 17; 65 cases have been recorded in adults, and 21 in children under age 5, an age group too young in many cases to have completed the standard two-dose vaccination series. Five people have been hospitalized. No deaths have been reported.

Wisconsin health officials have repeatedly noted that the outbreak's growth traces almost entirely to unvaccinated individuals, underscoring the protective value of the measles-mumps-rubella vaccine, which is roughly 97 percent effective against the disease after two doses and about 93 percent effective after one, according to the department's measles information page. Investigators have not identified a specific public venue, such as a store or event, where an unknown number of people might have been exposed, which the department says indicates the current spread is occurring through close personal contact within the community rather than at large gatherings.

How the outbreak took hold

The outbreak's origins trace to early August. Wisconsin recorded its first two measles cases of 2026 in cases linked to travel outside the state. Weeks later, the department disclosed two additional cases — one in Iowa County, one in Lafayette County — that investigators determined were not connected to either the travel-linked cases or to each other. In an August 11 release confirming those cases, the department's chief medical officer for communicable diseases, Dr. Ryan Westergaard, said the pattern pointed to a problem beyond the four identified patients. "The rapid emergence of these cases, particularly among people who have not traveled outside of Wisconsin, indicates that there is active local transmission, and it's very likely that additional cases exist in the community that have not yet been identified or reported to public health," he said.

That assessment proved accurate. Case counts climbed from roughly nine in mid-August to 36 by August 18, then to 41 confirmed and seven probable by August 21, passing 100 total cases by the start of September and reaching the current tri-county total of 157 by September 8. Fox6 Milwaukee's ongoing case tracker has logged the week-by-week climb, which has continued even as local and state health departments worked to identify and notify people who may have been exposed.

The underlying vulnerability, according to state data, is a vaccination rate that has fallen below the threshold epidemiologists say is needed to prevent sustained spread. Wisconsin's kindergarten MMR vaccination rate rose only slightly, from 84.8 percent in the 2024-2025 school year to 85.1 percent in 2025-2026, while the share of children with non-medical vaccine exemptions climbed from 6.3 percent to 7.3 percent over the same period. Public health researchers generally put the vaccination coverage needed to prevent measles from establishing sustained transmission in a community at around 95 percent, a level Wisconsin schools have not approached in recent years.

Who is affected, and what officials are urging

The outbreak is concentrated in a largely rural stretch of southwestern Wisconsin near the Iowa border, but health officials have stressed that the risk extends beyond the three counties currently reporting cases, particularly given how contagious measles is and the mobility of families across county lines as the school year begins. Households with unvaccinated children, along with infants too young to be vaccinated, face the highest risk of severe illness; one in four people who contract measles nationally end up hospitalized, according to the state health department, a statistic borne out by the five hospitalizations already tied to this outbreak.

On September 3, as students statewide returned to classrooms, the department issued a statement urging families to confirm their children's immunization status before the risk of classroom exposure grew. "Now is the best time for families to make sure their children have the protection they need to support their own health, and the health of their classrooms," said State Health Officer Paula Tran.

"Higher vaccination coverage can help prevent a single case in a school from turning into a community-wide outbreak," said Stephanie Schauer, director of the Wisconsin Immunization Program.

The department has directed families to verify vaccination records through the Wisconsin Immunization Registry or a healthcare provider, and has pointed to the federal Vaccines for Children and Vaccines for Adults programs, which cover the cost of immunizations for people who are uninsured, underinsured or otherwise unable to afford them. Wisconsin residents with questions about where to find a vaccine provider have been directed to call 211.

What happens next

State and county health departments said the investigation into the outbreak's spread remains active, with case counts likely to keep rising for at least several more weeks given measles' incubation period of 10 to 21 days between exposure and the onset of symptoms, which include high fever, cough, runny nose, conjunctivitis and the disease's characteristic rash. That lag means people exposed to cases confirmed in late August or early September may not become symptomatic — or be counted in official tallies — until later in September.

Wisconsin's outbreak is unfolding against a national backdrop in which measles activity has already outpaced recent years; federal health officials have reported thousands of confirmed cases across dozens of jurisdictions nationwide in 2026, with the overwhelming majority tied to identifiable outbreaks rather than isolated travel-related infections, and with kindergarten vaccination rates nationally continuing a multiyear decline. Wisconsin health officials have not set a timetable for when they expect the southwestern outbreak to be brought under control, saying instead that the pace of new cases will depend on how quickly unvaccinated residents in the affected counties get immunized and how consistently people who develop symptoms isolate and seek testing before contacting others.

The state has also turned its attention to higher education, issuing guidance to colleges and universities in the outbreak region about screening incoming students' immunization records and preparing isolation plans for dormitory residents who may be exposed, given the likelihood that the outbreak could reach campuses as the fall semester gets underway. County health departments in Grant, Iowa and Lafayette counties continue to conduct contact tracing on each newly confirmed case, a labor-intensive process that involves identifying everyone a patient may have exposed during the period before their rash appeared, when the virus is most transmissible. For now, the department's guidance to families remains unchanged: confirm vaccination status, watch for symptoms after any possible exposure, and call ahead before visiting a doctor's office or emergency room to avoid exposing other patients while awaiting testing results.