Canada has lost its measles elimination status, said the Pan American Health Organization (Paho) on Monday, after failing to curb an outbreak of the virus for 12 consecutive months.
Because Canada is no longer deemed measles-free, the Americas region as a whole has lost its elimination status, although individually the other countries are still considered to have stamped out the disease.
The US, however, risks losing its status as well if it does not stop an ongoing outbreak by January. Related cases have now been reported in Utah, Arizona and South Carolina.
Canada's outbreak began last October, with health officials attributing it to fewer people being vaccinated against measles.
At a news conference on Monday, Paho officials appealed to Canadian governments and the public to ramp up vaccinations, noting that 95% of the population needs to be immunised to stop the spread of measles.
"This loss represents a setback, but it is also reversible," said Dr Jarbas Barbosa, the health organisation's director.
The Public Health Agency of Canada said in its own statement that it is collaborating with Paho and regional health authorities to improve vaccine rates and strengthen data sharing.
Prior to Monday, Canada had been declared measles-free for three decades. It can regain its elimination status if it can curb spread of the measles strain associated with the current outbreak for at least 12 months.
The country has reported more than 5,000 measles cases in 2025, with most of them in the provinces of Ontario and Alberta. That is three times the 1,681 cases reported in the US, despite Canada's much smaller population.
The bulk of the outbreak has been in "under-vaccinated communities", Canadian health officials have said.
Vaccination rates in Alberta, one of the provinces hit hard by the outbreak, are lower than the 95% threshold, according to provincial data.
One region, the South Zone, located south of the province's largest city Calgary, reported only 68% of children under the age of two were immunised against measles as of 2024.
The MMR vaccine is the most effective way to fight off the dangerous virus, which can lead to pneumonia, brain swelling and death. The jabs are 97% effective and also immunise against mumps and rubella.
Canadian immunologist Dawn Bowdish told the BBC that there are many reasons behind the low vaccination rates, including lack of access to general practitioners, the absence of a national vaccination registry that Canadians could use to check their immunisation status, and the spread of misinformation.
She also noted a lack of public health outreach to communities that have been hesitant or distrustful of vaccines.
"It highlights how many of our systems broke down to get us to this point," said Prof Bowdish of McMaster University in Hamilton, Ontario.
"I hope that it will be a wake-up call to policymakers, and that it will be enough of a national embarrassment that we remedy some of those systemic issues," she added
The Americas is the first and only region in the world to have been declared measles-free, starting in 2016. That status was then briefly lifted after outbreaks in Venezuela and Brazil. The two countries regained elimination status in 2024, in part through coordinated vaccine efforts where millions were immunised.
But measles has since spread again, now in North America.
Along with Canada and the United States, Mexico has also seen a surge in cases and now ranks among the top 10 countries with the largest outbreaks, according to the US Centers for Disease Control and Prevention.