Measles cases in the United States are surging, with nearly 1,200 infections reported across 35 states in 2025. This resurgence marks a significant public health concern, potentially representing the largest outbreak in a quarter-century. Health officials are particularly concerned as even some fully vaccinated individuals are contracting the disease.
The Centers for Disease Control and Prevention (CDC) reports that approximately 3% of confirmed measles cases involved individuals who had received both doses of the MMR vaccine, considered fully vaccinated. An additional 2% of cases occurred in those who had received one dose. While the MMR vaccine is highly effective – 97% after two doses and 93% after one – these breakthrough cases underscore the complexities of vaccine efficacy and disease transmission.
This outbreak is approaching the scale of the 2019 outbreak, which saw 1,274 cases nationwide. Tragically, three deaths have already been attributed to measles this year: two children and one adult. This grim statistic highlights the potential severity of the disease, particularly for vulnerable populations.
Measles was declared eradicated in the U.S. in 2000, a testament to the success of widespread vaccination efforts. Eradication meant that new cases stemmed solely from international travel, with no domestic spread. However, recent declines in vaccination rates are threatening this progress.
Data from Johns Hopkins University indicates that vaccination rates have decreased by an average of 2.67% in many U.S. counties over the past five years. This decline pushes more communities below the critical 95% threshold needed for herd immunity, leaving them vulnerable to outbreaks.
The CDC emphasizes that the effectiveness of the measles vaccine can be influenced by the timing of vaccination relative to exposure. Vaccination within three days of exposure in controlled settings, such as schools, might offer some protection or lessen the severity of the illness. However, the agency notes that post-exposure vaccination is less effective in situations involving intense and prolonged close contact, such as households.
Interestingly, even prominent figures once known for expressing vaccine skepticism have publicly endorsed the MMR vaccine in light of the outbreak. Robert F. Kennedy Jr., currently serving as Health and Human Services Secretary, recently stated on social media that the MMR vaccine is "the most effective way to prevent the spread of measles." The CDC has been contacted for further comment.