Measles surges 31-fold in Americas this year, Canada worst hit; 71% cases unvaccinated

Health authorities have reported that measles cases in the Americas have surged dramatically this year, with more than 11,300 confirmed infections and 23 deaths recorded in ten countries as of mid-September. The Pan American Health Organisation (Paho) has stated that this represents a 31-fold increase compared to the same period in 2024, when just 358 cases were confirmed.

The sudden escalation has led Paho to call for urgent action emphasising that vaccination remains the most effective safeguard against a disease that had once been close to eradication in the region. The transmission was being driven largely by imported cases and spread quickly among communities with low vaccine coverage.

Canada at the epicentre

Among the countries affected, Canada has been identified as the hardest hit, accounting for more than 4,800 cases and one death. Mexico has reported a similar burden, with over 4,500 cases and 19 fatalities, while the United States has confirmed more than 1,400 cases and three deaths. Together, these three nations represent 96 per cent of all confirmed cases in the region.

The resurgence has shaken confidence in Canada’s long-standing measles elimination status, first achieved nearly three decades ago. Epidemiologists have said that declining vaccination coverage in recent years created conditions ripe for an outbreak. Coverage in Canada fell from around 90 per cent in 2019 to below 83 per cent by 2023, leaving large populations vulnerable when imported cases arrived, The Globe and Mail reported.

Imported sparks local flames

Investigations have shown that the current wave of infections originated largely from imported strains. More than 70 per cent of confirmed cases in the Americas were classified as importation-related, with 16 per cent traced directly to travel-linked sources.

One significant ignition point was traced back to a wedding in Florenceville, New Brunswick, in October 2024. The bride’s sister, who had travelled from Thailand, unknowingly attended while infectious. Within days, she was hospitalised with measles, and guests who returned home across provinces and into the United States began spreading the virus further, The Globe and Mail reported.

The outbreak eventually accounted for thousands of infections across Ontario, Alberta and several other provinces, contributing to Canada’s disproportionate burden.

Vulnerable groups, preventable deaths

The highest incidence was among infants under one year of age, followed by children aged one to four. Paho has noted that more than 71 per cent of confirmed cases occurred in unvaccinated individuals, while vaccination status as unknown in an additional 18 per cent.

The organisation has highlighted that measles is one of the most contagious human viruses, with an R0 reproductive number of 12–18, meaning a single case can infect the vast majority of susceptible contacts. Experts have stressed that while most recover after fever and rash, complications such as pneumonia, encephalitis and death remain real threats.

Global spread and regional gaps

While the Americas have experienced a dramatic resurgence, measles remains a global concern. The World Health Organisation (WHO) has reported more than 164,000 confirmed cases worldwide this year, across 173 countries, with the Eastern Mediterranean, Africa and Europe accounting for the majority of infections.

Despite some recent improvements, vaccination coverage across the Americas still falls short of the levels required to prevent outbreaks. Paho data shows that coverage for the first dose of measles-containing vaccine reached 89 per cent in 2024, while second-dose coverage was just 79 per cent. Only a small proportion of countries achieved the 95 per cent threshold required to sustain herd immunity, with nearly half reporting second-dose coverage below 80 per cent.

Role of hesitancy and access

Vaccine hesitancy and barriers to access in rural and marginalised urban areas are among the main reasons for the resurgence. In Thailand, where outbreaks have been a recurring challenge, officials observed similar patterns. At one school in the south of the country, roughly one in five students was unvaccinated due to parental fears and misinformation. What began as a handful of cases soon grew into nearly 100, forcing school closures and spreading to other regions—and eventually beyond Thailand’s borders, The Globe and Mail reported.

Canadian outbreaks followed similar dynamics. Health workers reported that many local communities were reluctant to cooperate with authorities turning instead to home remedies or alternative therapies. Public health experts have said such mistrust has hindered tracing and vaccination campaigns.

Consequences for elimination status

The scale of the resurgence has raised questions about whether Canada and the United States can maintain their measles elimination status, first declared by the WHO in 1998. The persistence of transmission, driven by imported cases and gaps in coverage, risks undermining decades of progress.

Paho’s recommendations for containment

In its latest update, Paho has urged governments to take immediate steps to contain transmission. The organisation has recommended that all countries achieve vaccination coverage of at least 95 per cent with two doses in every municipality. In addition, it has called for rapid vaccination of contacts of confirmed or suspected cases, intensified campaigns in outbreak zones and vitamin A supplementation to reduce the risk of severe complications.

Authorities have also been advised to strengthen surveillance in high-risk and border areas, implement rapid response plans and ensure hospital preparedness for isolating infectious patients. Paho has further recommended that travellers to areas with active transmission be vaccinated, including infants as young as six months in exceptional cases.

A cautionary tale

Epidemiologists have said that the resurgence of measles should be understood as a warning about the risks of complacency. Despite being preventable with a safe and effective vaccine available since 1963, measles continues to exploit gaps in immunity. In communities where vaccination levels have fallen, the virus has returned with speed and severity.

Combating misinformation, improving public trust and tailoring outreach to hesitant groups are now essential steps. In some countries, strategies have included home visits, digital messaging campaigns and incentives such as food support for families who vaccinate their children.

With global measles cases continuing to climb, the current outbreaks expose the fragility of progress. The Americas, once a model for measles elimination, now face the challenge of restoring confidence in vaccines and ensuring equitable access to immunisation services.

As one Thai epidemiologist put it, measles behaves like a tsunami, disproportionately threatening the most vulnerable. The only higher ground, he warned, remains vaccination.