A massive US measles outbreak has slowed but the start of the school year brings renewed risk of spread

CNN

06-08-2025

Texas hasn't reported a new outbreak-related measles case in nearly a month — a hopeful sign that one of the largest outbreaks the United States has seen in decades is starting to slow. But the measles threat hasn't faded as new outbreaks and growing case counts in other states add to the national tally.
There have been more measles cases reported in the US in the past month – at least 89 confirmed cases since the start of July – than in most years since the disease was declared eliminated a quarter century ago, according to data from the US Centers for Disease Control and Prevention.
And this year's total – 1,356 confirmed cases since January – is higher than it's been in more than 30 years. There have been 32 outbreaks this year, accounting for nearly 90% of all cases since January. Only 10 states remain at zero cases reported this year.
The start of the school year in the US poses new threats for the spread of measles amid a record-breaking year for cases and lagging vaccination rates.
Experts say that declining childhood vaccination rates across the US coupled with ongoing spread of measles in the US – and large outbreaks in neighboring Canada and Mexico – have raised concerns as children start to gather for the new school year.
'Nobody has a crystal ball, but the conditions are there to see an increased number of cases,' said Dr. Catherine Troisi, an infectious disease epidemiologist at UTHealth Houston.
On Saturday, Wisconsin reported nine new cases – all linked to the same exposure during travel to another US state. The state health department isn't releasing more details about the cases – including the vaccination status of the individuals or the specific state they traveled to – in order to 'balance individual privacy for what the public needs to know' and because the risk of community spread is considered to be low, Dr. Ryan Westergaard, chief medical officer in the Wisconsin Department of Health Services Bureau of Communicable Diseases, said at a news briefing on Monday.
But new data published by the CDC last week shows that kindergartners in Wisconsin had one of the lowest rates of coverage with the measles-mumps-rubella (MMR) vaccine. Only 84.8% of kindergartners had gotten the two recommended doses of the MMR vaccine last school year, well below the 95% threshold necessary to prevent an outbreak. Only Alaska and Idaho had lower MMR vaccination rates, the CDC data shows.
'Back-to-school brings a lot of kids together and measles is very, very infectious,' Troisi said. 'So if you bring kids together and one of them happens to have measles, that's just a great way to spread the virus.'
Declining vaccination rates also leave more kids vulnerable, she said, including those who are not vaccinated, those who are vaccinated but immunocompromised and those who are too young to be vaccinated.
'If you have more kids at risk, then the chance of measles spreading increases,' she said.
Wisconsin is one of just 15 states that allow parents to exempt their schoolchildren from required vaccines for 'personal conviction reasons,' in addition to religious beliefs or for medical reasons. There was a record rate of exemptions in the US last school year, CDC data shows, with about 3.6% of incoming kindergartners allowed to miss at least one required vaccine – and the exemption rate in Wisconsin was more than double that, at 7.6%.
The American Academy of Pediatrics says that non-medical exemptions to school immunization requirements should be eliminated, a longstanding position that the organization recently reaffirmed.
'Exempting children for nonmedical reasons from immunizations is problematic for medical, public health, and ethical reasons and creates unnecessary risk to both individuals and communities,' AAP leaders wrote in a policy statement last month. 'Although there are certainly families who would value having the option to decline vaccines and also send their children to school, nonmedical exemptions threaten the safety of the entire school community and shift the burden of protecting their children to the parents of children who are medically fragile, immunocompromised, or unable to receive immunizations for medical reasons.'
A new measles outbreak was announced in Michigan's Osceola County last week, with the original case resulting from an individual who was exposed to measles while traveling out of state. It's the third outbreak in the state, which has now reported at least 27 cases this year.
Wyoming also reported a batch of new measles cases on Saturday: four new cases in Carbon County were exposed to an individual with a confirmed measles infection, bringing the state's total up to seven.
Data from the Wyoming health department shows that Carbon County had some of the lowest vaccination rates among children in the state in 2023, ranking 21st out of 23 counties with just 66% of toddlers having gotten at least one dose of the MMR vaccine.
'County-level vaccination coverage estimates are important because public health issues often begin in small geographic areas and certain public health actions are most effective at the local level,' according to the Wyoming health department.
Unvaccinated individuals tend to be geographically clustered within certain communities, experts say, as families with similar sociocultural beliefs often live near each other.
'This phenomenon results in a greater likelihood of disease outbreaks when a vaccine-preventable illness is introduced into these communities,' AAP leaders wrote in the policy statement. 'Outbreaks that start in communities with low vaccination coverage have the potential to spread beyond those communities into other communities with low vaccination coverage or into the broader population, particularly for diseases like measles, varicella, and pertussis.'
While the start of the school year poses new risks, it also creates opportunities for trusted community leaders to encourage and promote vaccination, experts say.
'We do know that if vaccine clinics are held at schools, that will increase (coverage) just by making it easier for parents to get their kids vaccinated,' Troisi said. 'School nurses are respected, so having them talk about how important vaccines are is another strategy.'