## The Current Measles Outbreak in North America
The United States and Canada are grappling with one of their worst measles outbreaks in years, with the virus also crossing into neighboring Mexico. To date, approximately 2,500 cases and four deaths have been reported across these countries, a surge that’s been attributed to vaccine hesitancy. This article outlines what we know about the outbreaks, the nature of measles, and the implications for public health.
### What is Measles?
Measles is a highly contagious viral illness manifesting initially as symptoms like high fever, cough, runny nose, red or watery eyes, and light sensitivity. Within a few days post-infection, affected individuals typically develop a red, blotchy rash that starts on the face and spreads downwards. Additional symptoms include fatigue and loss of appetite.
While most individuals recover in two to three weeks, complications can arise, particularly among young children and those with weakened immune systems. These complications can be severe, leading to conditions such as ear infections, diarrhea, pneumonia, and encephalitis (brain swelling), which may cause permanent disability or even death. In higher-income countries, measles results in approximately one fatality for every 5,000 cases; however, in lower-income regions, the fatality rate can escalate to one in 100.
Before the measles vaccination was introduced in 1963, the United States recorded 3 to 4 million cases annually, resulting in hundreds of deaths and countless hospitalizations. Following widespread vaccination efforts, measles was declared “eliminated” in the U.S. by 2000, meaning no continuous transmission occurred for over a year.
### What is Herd Immunity?
Herd immunity refers to a phenomenon where a sufficient portion of a community becomes immune to a disease, either through vaccination or prior infection. For measles, herd immunity requires about 95% of the community to be immune, making it difficult for the virus to spread. This critical mass of immunity helps to protect individuals who cannot be vaccinated, including newborns and others with specific health issues.
Experts emphasize that the safest means of achieving and maintaining herd immunity is through vaccination, particularly given the severe risks associated with measles infections.
### How Effective is the Measles Vaccine?
According to the World Health Organization (WHO), measles vaccinations have prevented an estimated 31.7 million deaths globally from 2000 to 2020. The measles, mumps, and rubella (MMR) vaccine, which is widely utilized, offers approximately 97% protection against the virus. Typically, children receive the first dose at around 12 months of age, followed by a second dose at approximately three years and four months.
Incidents of breakthrough cases — vaccinated individuals contracting measles — are rare and generally mild.
### Where Has Measles Spread in North America?
The current measles resurgence has impacted North America significantly, with more than 2,500 confirmed cases spread across the U.S., Canada, and Mexico. Tragically, three deaths have occurred in the U.S. and one in Mexico. The outbreak originated in late 2024 in Ontario, Canada, and subsequently spread to Texas and northern Mexico in early 2025, particularly affecting Mennonite communities, a demographic historically under-vaccinated.
A WHO report from April indicated that measles incidents in the Americas during the first quarter of 2025 were 11 times higher compared to the same period in 2024.
#### United States
The U.S. has documented 935 confirmed measles cases across 30 states, with Texas representing the outbreak’s epicenter by accounting for 683 cases. The disease has also been noted in New Mexico (67 cases), Oklahoma (16 cases), and Kansas (37 cases). Notably, three individuals died from measles-related complications between February and April of 2025.
#### Canada
Canada is facing its most severe measles outbreak in over 25 years, with Ontario reporting more than 1,000 cases since October 2024. The outbreak traced back to a significant gathering in New Brunswick province involving Mennonite communities.
#### Mexico
In Mexico, particularly in the northern state of Chihuahua, cases of measles have surged dramatically this year, with 786 cases reported so far compared to just seven the previous year. A 31-year-old unvaccinated man from Ascension, Chihuahua, succumbed to the disease in early April.
### Why is Measles Spreading?
The primary driver of the measles resurgence is vaccine hesitancy. Misinformation and a decline in vaccination rates have been noted, leading to a drop below the threshold necessary for sustaining herd immunity.
Exemptions for vaccinations based on personal or religious grounds are becoming more prevalent in certain U.S. states and Canadian provinces. This trend has facilitated the existence of clusters of unvaccinated individuals, creating conditions ripe for outbreaks.
According to the U.S. CDC, during the 2023-2024 school year, non-medical vaccination exemptions were reported by 3.3% of preschool children, compared to 3% the previous year. Some states experience exemption rates exceeding 5%.
Health officials acknowledge the interconnectedness of communities across the U.S., Canada, and Mexico, particularly among Mennonite groups who maintain strong cross-border relationships and possess lower vaccination rates, making it easier for the virus to spread.
### Who Are the ‘Anti-Vaxxers’ and What Are Their Concerns?
Anti-vaccine advocates, often labeled as “anti-vaxxers,” hold a range of concerns regarding vaccinations. These apprehensions include fears about side effects, distrust in pharmaceutical companies or government health authorities, and personal or religious beliefs.
Mennonite communities in Ontario and Chihuahua have shown historical hesitancy towards vaccinations, and recent measles cases in these areas are predominantly among this population.
One enduring myth contributing to vaccine hesitancy is the unfounded belief that vaccines are linked to autism, originating from a discredited 1998 study.
### Will Trump’s Pick of RFK Jr. as Health Secretary Push Vaccination Levels Down Further?
The potential appointment of Robert F. Kennedy Jr. as the U.S. Secretary of Health and Human Services has raised alarm among health experts, particularly as measles cases are surging across North America. Kennedy, a notable vaccine skeptic, has propagated false claims regarding vaccines’ association with autism and has made misleading assertions about the MMR vaccine containing “aborted fetus debris.”
Public health experts have thoroughly debunked these claims, clarifying that the rubella component of the vaccine derives from lab-grown cells, not fetal tissue.
Kennedy has been criticized for downplaying the urgency of the current outbreak and endorsing unproven treatments, such as vitamin A supplements, which lack robust scientific support. Furthermore, his management changes within the Department of Health and Human Services, including staff cuts and budget reductions for crucial agencies like the CDC, could undermine the nation’s capacity to effectively respond to health crises.
