The US and Canada have experienced one of the worst measles outbreaks over the years, but the virus has also traveled to nearby Mexico.
A total of 2,500 cases and four deaths have been reported. Hesitancy to vaccines has been criticized.
This is what we know about the outbreak so far and why measles cases are on the rise.
What is measles?
Measles is a highly contagious viral disease that starts with symptoms such as high fever, cough, runny nose, red or water-like eyes, and sensitivity to light. A few days after infection, a rash with red spots usually appears on the face and spreads across the body. Fatigue and loss of appetite are also common.
Most people recover within 2-3 weeks, but complications are particularly severe in young children and those with weakened immune systems.
These include ear infections, diarrhea, pneumonia, and brain swelling (encephalitis), which can lead to permanent disability or death. In wealthy countries, every 5,000 measles causes about one death, while in low-income regions where the health care system is weak, the fatality rate is one in 100.
Before the measles vaccine was introduced in 1963, around 3-4 million measles were reported in the United States each year, with hundreds of deaths and thousands of hospitalizations. By 2000, measles had been declared “excluded” in the United States following widespread vaccinations. This means that there was no continuous infection of the disease for more than 12 months. Countries that have eliminated the disease via vaccines are believed to have “swarm immunity” as long as the vaccine continues to be offered to everyone.
What is herd immunity?
Swarm immunity occurs when sufficient people in the community become immune to the disease by receiving vaccinations or recovering from infection.
The number of people who need to be immunized to achieve herd immunity across the community depends on the disease. Measles, which spreads very easily, requires 95% of the community to be immunized.
If most people are immune, the disease is much more difficult to spread. This means that you are more likely to die before it is transmitted to other hosts. This helps protect people who are unable to get vaccinated for certain reasons, such as newborns and people with certain health conditions.
Experts say the safest way to maintain immunity in herds is through vaccination due to the potentially serious effects of measles infection.
How effective is the measles vaccine?
According to the World Health Organization (WHO), measles vaccinations prevented an estimated 31.7 million deaths worldwide between 2000 and 2020.
According to public health agencies, the widely used measles, mumps and rubella (MMR) vaccines offer around 97% protection against the measles virus.
Vaccines are usually given to children in two stages. It’s the first dose at 12 months and the second time in about three months (if your child is approaching preschool age) as part of a country’s regular vaccination programme like the UK.
Groundbreaking cases of people vaccinated are rare and usually mild.
Where is measles spreading in North America?
North America has experienced a major measles revival, with over 2,500 lawsuits confirmed in the US, Canada and Mexico. Three deaths occurred in the US, one in Mexico. The outbreak began in Ontario, Canada in late 2024 and spread to Texas and northern Mexico in early 2025, with the most difficult population in the Mennonite community (Anabaptist Christian Church), a historically unvaccinated population.
According to a WHO report in April, the measles incident in the Americas for the first three months of the year was 11 times higher than the same period in 2024. He said the region now faces a “high” risk of measles occurrence compared to “moderate” risk.
US
The US has reported 935 confirmed cases of measles in 30 states so far, with Texas being the epicenter of the outbreak and accounting for 683 of these cases. The outbreak has now spread to New Mexico (67 cases), Oklahoma (16) and Kansas (37).
Three died of measles between February and April. This includes two unvaccinated children in Texas and one unvaccinated adult in New Mexico. These mark the country’s first measles death since 2015.
In 2019, the US experienced the most significant outbreak of measles since 1992, with 1,274 confirmed cases reported in 31 states, but no deaths.
Canada
Meanwhile, Canada has experienced the worst measles outbreak in over 25 years. Since mid-October 2024, it has recorded over 1,000 cases in Ontario alone.
Canadian officials confirmed that the outbreak came from a large gathering in New Brunswick that involved the Mennonite community, which tends to shun modern technology and medicine, aiming for a simple life.
Mexico
In Mexico, the number of measles cases, which have been reported to date in northern Chihuahua this year, has risen sharply this year. Last year, only seven cases were reported nationwide. Ascension’s 31-year-old unvaccinated Chihuahua passed away from illness in early April.
Why does measles spread?
According to the WHO and the US Centers for Disease Control and Prevention (CDC), the main reason for the spread of measles is that few people are taking the vaccine. Increased misinformation and hesitance have led to a decrease in vaccination rates below the levels required for herd immunization.
In some US and Canadian states, exemptions that give non-medical reasons to reduce vaccines for personal or religious reasons are becoming more common. This led to the presence of clusters of non-vaccinated people who are more vulnerable to outbreaks when exposed to the virus.
The US CDC reported that during the 2023-2024 academic year, one or more vaccine exemptions were billed by 3.3% of kindergarten parents or caregivers, compared to 3% in the previous year. Exemptions are high in 40 states and the District of Columbia, with 14 states reporting exemption rates above 5%.
Health officials point to how closely related the affected communities in the US, Canada and Mexico are, and people often travel between them. In particular, Mennonite groups have a strong cross-border ties and low vaccination rates, making it much easier for the virus to spread from one area to another.
Who are the “anti-vaxers” and what are their concerns?
Anti-vaccine advocates, often referred to as “anti-vaxxers,” oppose vaccination for several reasons, including side effects, distrust of pharmaceutical companies and government agencies, and religious or personal beliefs.
Mennonite groups in Ontario and Chihuahua have also been hesitant to take the vaccine historically, and health officials say a significant portion of recent measles incidents in these areas are concentrated within this population.
One of the most sustained myths driving vaccines is the claim that vaccines cause autism. This belief comes from a 1998 study, and has since been discredited and retracted.
Will Trump choose RFK JR if health secretaries lower vaccination levels even further?
The appointment of Robert F. Kennedy Jr. as secretary to the U.S. Department of Health and Human Services has sparked concern among health experts, particularly as measles cases are on the rise in North America.
Longtime vaccine skeptic Kennedy has repeated the false claims that the vaccine is linked to autism and that the MMR vaccine contains “discontinued fetal fragments.”
Health experts have exposed this claim. The rubella portion of the vaccine was made using laboratory-grown cells copied from a single fetal sample taken in the 1960s. These cells have been lab-mounted for decades and are used to grow the viruses needed for vaccines. However, the cells themselves are removed during the process, so there is no fetal tissue in the actual shot.
Kennedy has been criticized for downplaying the severity of current measles outbreaks and promoting unproven treatment for measles. He proposes alternatives such as vitamin A supplements and cod liver oil. Experts say it has not replaced vaccinations and is not supported by strong scientific evidence.
Kennedy has also made major changes to the Department of Health and Human Services, fired thousands of employees and cut budgets for key agencies like the CDC.
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