When a region declares itself free of measles, it represents years of hard work, millions of vaccinations, and careful disease tracking. But what does "measles-free" really mean? How do public health officials decide when a region qualifies for this designation, and what happens when measles comes back? As North America faces a surge in measles cases in 2025, these questions are more pressing than ever.
What Does Measles Elimination Actually Mean?
is not the same as wiping measles off the face of the Earth. Instead, it means stopping the continuous spread of the measles virus within a specific geographic area for at least . Think of it this way: even in a measles-free region, someone could catch measles while traveling abroad and bring it home. That person might even pass it to a few others. But in a region that has truly eliminated measles, the virus runs out of steam because so many people are vaccinated. The outbreak stops on its own, usually affecting only a small number of people who were not protected by the vaccine.
The key difference between elimination and simply having low case numbers is whether the virus can sustain itself. happens when a chain of infections continues uninterrupted for 12 months or more. When this chain is broken for at least a year and the region can prove it through good disease tracking, that region can be verified as having eliminated measles.
The Guardians of Measles-Free Status
The establishes the framework for verifying measles elimination, but the actual certification happens at the regional level. Each of WHO's six regions has its own made up of independent experts in fields like infectious disease, public health, and laboratory science.
For North America, this responsibility falls to the , which oversees the entire Americas region stretching from Canada to Argentina. PAHO established the to make these determinations. These experts meet regularly to review detailed reports from each country, conduct site visits when needed, and ultimately decide whether a nation has achieved, maintained, or lost its measles-free status.
The commission members serve without payment and must be independent, meaning they cannot be directly involved in running the vaccination or disease surveillance programs they evaluate. This helps ensure their assessments remain objective and based purely on the evidence.
What Countries Must Prove
To be verified as measles-free, countries need to demonstrate success across : disease patterns over time, population immunity levels, quality of disease surveillance, program sustainability, and molecular evidence from laboratory testing.
For disease patterns, countries must show that measles cases have dropped dramatically and that any outbreaks have been quickly contained. The target is fewer than in the population. Imagine a city of one million residents. Even a single confirmed case exceeds this threshold, though having one or two isolated imported cases does not automatically disqualify a region if they can prove those cases did not lead to sustained transmission.
Population immunity depends primarily on vaccination. The measles vaccine works remarkably well. After , about 97% of people develop protection that lasts a lifetime. But measles spreads so easily that even a small percentage of unvaccinated people can allow outbreaks. This is why public health agencies aim for at least to receive two doses of the measles vaccine. When this coverage level is reached throughout a population, it creates what scientists call herd immunity, protecting even those few people who cannot be vaccinated due to medical reasons.
The surveillance requirement is where things get technical, but the principle is straightforward: countries must prove they are looking hard enough to find measles cases. It's not enough to simply report no cases. Countries need to demonstrate they have a system sensitive enough to detect cases if they exist. They measure this through several benchmarks. One key measure is the , which counts how many people with fever and rash turn out NOT to have measles after testing. The target is at least two such cases per 100,000 people each year. This might seem backwards, but it makes sense: if health workers are actively investigating everyone with measles-like symptoms and collecting blood samples for testing, they will inevitably find people whose symptoms were caused by something else. Finding these non-measles cases proves the system is working.
Another surveillance benchmark requires that or counties within a country investigate and test at least one suspected measles case each year. Again, this ensures the surveillance system reaches every corner of the country, not just major cities. When samples are collected, they should be taken of when the rash first appeared, and results should come back quickly so public health teams can respond.
Laboratory testing provides the molecular evidence. Modern techniques allow scientists to determine the genetic fingerprint of measles viruses. Different strains circulate in different parts of the world. By analyzing the virus from each case, scientists can determine whether a case represents an imported virus from another country or a locally circulating strain. If the same viral genotype keeps appearing over many months, it suggests ongoing transmission within the community. Countries approaching elimination typically see a variety of imported genotypes appearing sporadically rather than one genotype persisting month after month.
Finally, countries must demonstrate that their programs are sustainable. Verification commissions want to see that countries have adequate funding, trained personnel, functioning laboratories, and political commitment to maintain these efforts over time. A country that achieves elimination through a one-time heroic effort but cannot maintain its systems will likely lose that status when vigilance fades.
The Process of Verification
The verification process operates like a careful audit. Each country establishes a made up of local experts who compile evidence and prepare annual reports. These reports include detailed information on every measles case: when and where it occurred, the vaccination status of the infected person, laboratory results, and whether the case was linked to other cases or represented an isolated imported infection.
The national committee reviews immunization coverage data across all regions of the country, examines surveillance performance indicators, and analyzes trends over multiple years. They conduct site visits to health facilities and laboratories to verify that systems are functioning as reported. After assembling this evidence, they submit their report to the regional verification commission.
The regional commission then carefully reviews these reports, looking for gaps or inconsistencies. Commission members may request additional information or clarification. Sometimes they conduct their own field visits to see operations firsthand. After a thorough evaluation, the commission makes a determination about each country's status.
For countries seeking initial verification of elimination, they must demonstrate of interrupted transmission. Once verified, countries must continue submitting annual reports to maintain their status. This ongoing monitoring is essential because elimination can be lost.
From Success to Setback: Countries That Lost Measles-Free Status
The history of measles elimination includes inspiring successes but also sobering setbacks. Several countries have earned measles-free status only to lose it when outbreaks re-establish continuous transmission.
The provides a well-documented example. The UK achieved measles elimination in 2017 after demonstrating three years of interrupted transmission. But in 2018, measles cases surged. By the first quarter of 2019, the country had recorded 231 confirmed cases, and the same measles strain had circulated for more than 12 months. In August 2019, WHO .
What happened? Vaccination coverage had gradually declined. While about 95% of UK children received the first dose of the measles vaccine, only , well below the 95% target needed for both doses. Travelers brought measles back from outbreaks occurring in other European countries, and the virus found pockets of unvaccinated people where it could spread. Public health officials also pointed to the role of vaccine misinformation spreading on social media, which contributed to hesitancy among some parents.
The UK was not alone. In 2019, lost their measles elimination status alongside the UK. Albania, the Czech Republic, and Greece all saw measles transmission re-establish itself despite having previously achieved elimination. All four countries had what public health officials described as "extremely high" national vaccination coverage, but the coverage was not uniform across all communities. As one WHO official noted, achieving high national coverage is not enough. It must be achieved "in every community, and every family for every child."
Closer to home, provides another example. The Americas region became the first in the world to eliminate measles in 2016. It was a historic achievement. But in 2018, measles outbreaks began in Venezuela and Brazil, linked to population movements and declining vaccination coverage. Brazil's outbreak proved particularly severe. By the time transmission was finally interrupted, more than had been infected. In February 2019, WHO revoked Brazil's measles-free status because transmission had continued for more than 12 months. Venezuela lost its status in July 2018 for the same reason.
The Path Back: Countries That Regained Elimination Status
Here is the encouraging news: losing measles-free status does not have to be permanent. With determined effort, countries can regain elimination.
Brazil offers the best recent example of this recovery. After losing its status in 2019, Brazil implemented an aggressive response. Health officials used a technique called to ensure vaccination activities reached every community, including remote areas. They decentralized laboratory testing, so results came back faster. They trained rapid response teams who could quickly investigate and contain any new cases.
These efforts paid off. Brazil recorded its last case of endemic measles in June 2022. After demonstrating more than a year without transmission, Brazil was , restoring the Americas region's measles-free status.
Venezuela followed a similar path, regaining its measles-free status in 2023 after five years of sustained effort to rebuild vaccination programs and surveillance systems.
The in 2021, though this recovery had an unusual component. The COVID-19 pandemic led to dramatic decreases in international travel, which reduced the importation of measles cases globally. This gave countries like the UK breathing room to interrupt transmission chains. However, the UK's second-dose vaccination coverage has continued to decline, and in 2024, the country recorded , putting its elimination status in jeopardy once again.
These examples show that regaining elimination status is possible but requires the same elements that achieved it initially: high vaccination coverage, strong surveillance, rapid outbreak response, and sustained commitment.
The Current Crisis in North America
As of late 2025, the Americas region faces its most serious measles challenge since regaining elimination status. across North, Central, and South America reported measles outbreaks during the year, with more than 11,000 confirmed cases and 23 deaths by September. This represents a 31-fold increase compared to the same period in 2024.
Three countries account for the vast majority of cases. , with one death by mid-September. The outbreak began in October 2024, when someone who had been infected abroad attended a wedding in New Brunswick. From there, measles spread across nine provinces and one territory. Some experts expressed shock at the scale. As one infectious disease specialist at the University of Alberta said, "I never in my life thought I'd see a massive measles outbreak in Canada. Most of my career in infectious diseases, there's been 10 cases a year or less."
and 19 deaths by mid-September, with 93% of cases concentrated in the state of Chihuahua. Indigenous communities were hit particularly hard, experiencing a death rate 20 times higher than the general population. The Mexican government launched a mass vaccination campaign targeting people aged 6 months to 49 years in affected areas.
The and three deaths by mid-September, with outbreaks in 41 jurisdictions. The largest outbreak affected under-vaccinated Mennonite communities across New Mexico, Oklahoma, and Texas, with cases linked to similar outbreaks in Canada and Mexico.
Several smaller outbreaks occurred in other countries, including Bolivia, Argentina, Belize, Brazil, Paraguay, Peru, and Costa Rica.
The common thread across all these outbreaks is declining vaccination coverage. In 2024, first-dose measles vaccine coverage in the Americas reached 89%, while second-dose coverage reached only 79%. Both numbers fall needed to prevent outbreaks. Among reported measles cases with known vaccination status, 71% of infected people had never been vaccinated, and another 18% had unknown vaccination status.
What Happens Next?
To lose measles-free status officially, a country must have . For Canada, that deadline approached at the end of October 2025. The United States faces its deadline in January 2026, and Mexico faces its deadline in February 2026. The Regional Verification Commission will meet in late 2025 to review the evidence and determine each country’s status.
If these countries lose their measles-free designation, the entire Americas region would lose its status as the only region in the world to have eliminated measles. This would represent a major setback for public health, but not an insurmountable one. As Brazil and Venezuela demonstrated, countries can rebuild their programs and regain elimination status.
The path forward requires the same proven strategies that initially achieved elimination. Vaccination coverage must increase to at least 95% for both doses, and must reach every community. Surveillance systems must remain sensitive enough to detect every case. When cases appear, rapid response teams must investigate immediately, vaccinate contacts, and prevent further spread. Laboratory networks must quickly identify and characterize viruses. And perhaps most demanding of all, this work must continue year after year, even when measles seems like a distant memory.
Looking Ahead
Some regions have recently achieved elimination and are working to maintain it. In early 2025, WHO had collectively eliminated both measles and rubella. These island nations overcame enormous challenges, including vast distances between communities, limited resources, and logistical barriers to vaccine delivery. Their success demonstrates that elimination is achievable even under challenging circumstances when countries work together and maintain commitment.
The measles story is ultimately about sustained effort. Achieving elimination takes years of building strong immunization programs and surveillance systems. Maintaining elimination requires continuing that effort indefinitely. As vaccination coverage declines and measles cases increase across North America, the region stands at a crossroads. The tools to control measles are available: a safe and highly effective vaccine, proven surveillance methods, and detailed guidance from decades of elimination efforts worldwide. What remains to be seen is whether countries will commit the resources and attention needed to use these tools effectively.
The coming months will reveal whether North America can interrupt transmission quickly enough to maintain elimination status or whether the region will join the list of places that achieved this goal only to lose it. Either way, the experience will provide lessons for the global effort to eventually eradicate measles, making it the second human disease, after smallpox, to be eliminated from the planet. That day remains distant, but the work happening now in response to outbreaks in Canada, Mexico, and the United States will help determine how quickly the world can get there.