Following the measles outbreak in Canada that infected thousands of people over the past year, an international health body revoked the country’s measles-free status on November 10, 2025.
The Pan American Health Organization (PAHO), which serves as the World Health Organization’s (WHO) regional office for the Americas, made this announcement after the agency’s measles elimination commission met in Mexico City to review the latest public health data.
As a global health epidemiologist who studies the spread of infectious diseases, this change in status does not surprise me. Measles is highly contagious, and declining childhood vaccination rates in Canada and other countries have left many children unprotected against the disease.
The resurgence of measles in Canada after decades with very few cases is not an isolated problem. The United States has also suffered large measles outbreaks this year and will likely soon lose its disease-free status.
The loss of measles-free status is a symptom of a deeper problem: declining public trust in science and health messages, which has led to declining vaccination rates and increasing vulnerability to vaccine-preventable diseases.
What does it mean for a country to be measles-free?
Measles is one of the most contagious diseases on the planet. Before the measles vaccine was licensed in 1963, almost all children became infected and more than two million died from it each year. The vaccine dramatically reduced that risk. By 1968, five years after the vaccine became available, the number of cases in the United States had decreased by more than 95%. Cases in Canada also decreased substantially following the introduction of the vaccine.
Tragically, nearly 100,000 children continue to die from measles each year, despite the availability of a safe, effective and low-cost vaccine. Almost all of these deaths occur in low-income countries, where many children do not have access to recommended vaccines.
The WHO uses three categories to describe a country’s effectiveness in preventing the spread of infectious diseases such as measles. A disease is considered controlled when public health interventions, such as routine childhood vaccination, significantly reduce the rate of new infections. A disease is considered eliminated from a country when the only cases that occur are small outbreaks related to international travel.
And finally, a disease is considered eradicated only after several years without cases being recorded anywhere in the world.
To achieve measles elimination, a country must be free of local transmission of the disease for at least one year. It will lose this status if a chain of infections from person to person is recorded for more than one year. Once a country has eliminated measles, the risk of contracting the disease is virtually zero as long as vaccination rates remain high. But when vaccination rates decline, outbreaks will soon begin to occur.
Find out: America could lose its status as a measles-free zone due to continued outbreaks
What happened in Canada?
In 1998, the Pan American Health Organization confirmed that Canada had eliminated measles transmission. Two years later, the United States also earned the designation of a measles-free country.
By 2016, all countries in the Americas had achieved measles elimination. The region lost that status in 2018 after outbreaks in Brazil and Venezuela, and regained it in 2024.
However, childhood vaccination rates declined around the world, especially during and after the Covid-19 pandemic. To protect communities from measles outbreaks, approximately 95% of the population must be vaccinated against the disease.
In Canada, the percentage of 2-year-old children who have received at least one dose of measles vaccine decreased from about 90% in 2019 to about 82% in 2022 and 2023. As the number of unvaccinated people in the population increased, the risk of measles outbreaks grew.
After only 16 cases of measles were recorded nationwide between 2020 and 2023, the number of cases in Canada increased to more than 100 in 2024 and more than 5,000 in 2025. In 2025, cases were recorded among infants, children and adults in all Canadian provinces, and two infants died.
Less than 10% of people who have gotten sick had been vaccinated against the disease.
What will happen next?
Both the United States and Mexico are likely to lose their measles-free designation in 2026, as both countries have suffered sustained measles outbreaks since early 2025.
Although more than 90% of preschool children in the United States are vaccinated against measles, that rate is too low to protect communities from outbreaks. An outbreak that began in Texas in January 2025 infected more than 760 people and killed two children.
In total, more than 1,600 Americans in more than 40 states became sick with measles in 2025. That’s more cases than in any year since 1992. More than 90% of the people who got sick were unvaccinated.
Mexico also recorded thousands of measles cases this year, most among unvaccinated people.
Central America, South America and the Caribbean will maintain their status as measles-free countries for now. However, outbreaks in North America increase the risk of measles spreading to other countries.
Without significant improvement in vaccination coverage and public confidence in community health measures, many countries are likely to face more frequent and more severe outbreaks of measles and other vaccine-preventable diseases in the coming years.
*Kathryn H. Jacobsen is the William E. Cooper Distinguished Professor of Health Studies at the University of Richmond.
This article was originally published in The Conversation
Also read: Canada loses measles elimination status after three decades
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