Dr. Ryan Westergaard, chief medical officer for DHS, told reporters at a Thursday afternoon briefing that the actual number of infections is likely higher. "Not everyone who becomes infected gets tested or comes to the attention of public health," he said, calling the official count "almost certainly an underestimate." The 2026 case total is more than ten times the 36 cases reported in 2025. In most years over the previous decade, the state recorded zero or one measles case annually.

DHS officials declined to release additional details about the infant's death, citing the family's privacy.

The outbreak reflects a sharp decline in vaccination rates. Two doses of the MMR vaccine are about 97% effective at preventing measles, but Wisconsin's kindergarten vaccination rate has fallen to roughly 85%, well below the 95% threshold needed to prevent widespread transmission. Nationally, the rate is 92%.

"Measles is now spreading because there are enough people who are susceptible to infection for the virus to continue finding new hosts," Westergaard said. "That's really the central issue here."

Dr. Stephanie Schauer, the state immunization program manager, noted that vaccination coverage varies widely across Wisconsin, with some communities falling far below the statewide average. "We have many pockets in communities throughout Wisconsin that have these lower levels, that we are concerned if measles is introduced, we could see community spread," she said. "You have to really be aware of what are the rates at your school and in your community and in your county."

Measles is extraordinarily contagious. The airborne virus can linger in a room for up to two hours after an infected person leaves, and Westergaard said unvaccinated individuals face "a very high likelihood" of infection upon exposure. The illness typically begins with fever, cough, runny nose and red eyes, followed days later by a telltale rash. It can lead to pneumonia, brain inflammation, permanent disability and death.

"Measles was once a common childhood infection in the United States," Westergaard said. "What brought it under control was vaccination to the point that many physicians practicing today have never seen a case. That was an extraordinary public health achievement. But it wasn't permanent and it wasn't inevitable that we would have that success."

Statewide, health care providers have administered about 42,000 MMR doses since August. DHS has also issued new guidance recommending an early dose for infants aged 6 to 11 months who are at increased risk of exposure. Schauer said between 500 and 600 infants have received the early shot in the past three months.

The decline in immunization is not limited to MMR. A report released Thursday by the Wisconsin Policy Forum found that only 87.4% of K-12 students met all of the state's minimum school immunization requirements for the 2025-26 school year—a near-record low. The report cited several factors, including an expanded list of required vaccines, disruption and controversy surrounding COVID-19 vaccines, and an increase in families seeking personal conviction waivers to exempt children from school requirements.

The report recommends that public health officials work to reach students who are behind schedule, reduce the number of personal conviction waivers, and rebuild public trust in vaccines.

Schauer emphasized the need to ensure all children have access to vaccines and to raise awareness of the Vaccines for Children program, which provides free vaccines to families with no or inadequate insurance.

"This is a vaccine we've used for decades," Westergaard said. "We have extensive experience about its safety and its effectiveness."