by Kathryn H. Jacobsen,The Conversation

Credit: Nataliya Vaitkevich from Pexels

In the wake of ameasles outbreak in Canada that has infectedthousands of people over the past year, an international health agencyrevoked the country's measles-free statuson Nov. 10, 2025.

The Pan American Health Organization, which serves as the World Health Organization's regional office for the Americas, made this announcement after the agency'smeasles elimination commissionmet in Mexico City to review the latest public health data.

As aglobal health epidemiologistwho studies the spread of infectious diseases, this change in status does not surprise me. Measles is highly contagious, and a drop in childhood vaccination ratesin Canadaand in other countries has left many children unprotected from the disease.

The resurgence of measles in Canada after decades with very low numbers of casesis not an isolated problem. The U.S. has also hadlarge outbreaks of measles this year, and it will likely soon lose its measles-free designation as well.

The loss of measles elimination status is a symptom of a deeper issue:declining trustin public messaging about science and health, which has led to decreased vaccination rates and growing vulnerability to vaccine-preventable diseases.

Measles is one of the most contagious diseases on the planet. Before the measles vaccine waslicensed for use in 1963, nearly every child got measles infection andmore than 2 million children diedfrom measles each year.

The vaccine decreased that risk dramatically. By 1968, five years after the vaccine became available, case counts in the U.S. haddropped by more than 95%. Cases in Canada alsodecreased substantiallyafter the vaccine was introduced.

Tragically,about 100,000 children still die from measleseach year even though a safe, effective and low-cost vaccine is available. Almost all of those deaths occur in low-income countries where many children do not have access to recommended vaccines.

The World Health Organization usesthree labels to describehow well a country is preventing the spread of infectious diseases such as measles. A disease is said to be controlled when public health interventions such as routine childhood vaccinations significantly lower the rate of new infections. A disease is considered to be eliminated from a country when the only cases that happen are small outbreaks linked to international travel. And finally, a disease is deemed eradicated only after several years of no cases occurring anywhere in the world.

To achieve the status of measles elimination, a country must have no ongoing local transmission of the diseasefor at least one year. It will lose that status if it has a chain of cases that spread from person to person for more than one year.

Once a country has eliminated measles, there is almost no risk from the disease as long as vaccination rates stay high. But when vaccination rates drop, outbreaks will soon start happening.

In 1998, the Pan American Health Organizationconfirmed that Canada had eliminated measles transmission. Two years later, the U.S. alsogained the measles-free designation.

By 2016, every country in the Americas had achieved measles elimination status. The regionlost that status in 2018after outbreaks in Brazil and Venezuela, and thenregained it in 2024.

But childhood vaccination rateshave been falling worldwide, especially during and after the COVID-19 pandemic. To protect communities from measles outbreaks,about 95% of the populationmust be vaccinated against the disease.

In Canada, the percentage of 2-year-olds who have received at least one dose of measles vaccine dropped from about 90% in 2019 toabout 82% in 2022 and 2023. As the number of unvaccinated people in the population increased, the risk of measles outbreaks grew.

After having only 16 total cases of measles nationwide between 2020 and 2023, the number of measles cases in Canada jumped to more than 100 in 2024 andmore than 5,000 cases in 2025. Cases have occurred among infants, children and adults in every Canadian province in 2025, and two infants have died.

Fewer than 10% of the people who have gotten sick had been vaccinated against the disease.

It is likely that both the U.S. and Mexico will lose their measles-free designation in 2026, because both countries have hadsustained outbreaks of measlessince early 2025.

Althoughmore than 90% of kindergartners in the U.S.are vaccinated against measles, that rate is too low to protect communities from outbreaks. Anoutbreak that started in Texasin January 2025infected more than 760 peopleand caused the deaths of two children.

In total, more than1,600 Americansin more than 40 states have gotten sick from measles in 2025. That is more cases than any year since 1992. More than 90% of the people who got sick were unvaccinated.

Mexico has also hadthousands of measles cases this year, mostly among unvaccinated people.

Central America, South America and the Caribbean will retain their measles-free status for now. But the outbreaks in North America increase the risk of measles spreading to other countries.

Without a significant improvement in vaccination coverage andpublic trustin community health measures, many countries are likely to face more, and bigger, outbreaks ofmeaslesand othervaccine-preventable diseasesin the coming years.

This article is republished fromThe Conversationunder a Creative Commons license. Read theoriginal article.

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