The Pan American Health Organization (PAHO) confirmed on November 10, 2025, that the Americas have officially lost their status as a region free of endemic measles transmission, raising serious concern among public health authorities.

This change came after Canada, one of the 35 sovereign states in the region, experienced continuous circulation of the same measles strain for 12 months, which is a key criterion for determining endemic transmission.

For many health officials, the announcement marks a major setback after more than a decade of steady gains. The region first halted endemic measles in 2016, a milestone made possible through extensive vaccination efforts and coordinated public health actions. Only a year ago, the region had regained its measles-free designation, a milestone first achieved in 2016 after Brazil interrupted endemic transmission following an outbreak that began in 2018.

“This loss represents a setback, but it is also reversible,” said Jarbas Barbosa, MD, MPH, PhD, director of PAHO, at a press conference. “Today, we have more experience and better tools. If we act quickly and in a coordinated manner, we can achieve elimination once again.”

Regional Setback

According to PAHO’s latest data, as of November 7, 2025, the Americas reported 12,593 confirmed measles cases across 10 countries, with nearly 95% occurring in Canada, Mexico, and the US. This represents an approximately 30-fold increase from 2024. 

PAHO also confirmed 23 deaths in Mexico, three in the US, and two in Canada, underscoring the serious impact of an illness that remains fully preventable through vaccination.

The measles outbreak in Canada began in October 2024 in the province of New Brunswick and has since spread to nine of its 10 provinces, with more than 5000 confirmed cases. “The situation is concentrated in closed communities that are not very willing to be vaccinated; it is not a situation for the general population,” said Daniel Salas, MD, MPH, executive manager of PAHO’s Special Programme for Comprehensive Immunization.

Active outbreaks are ongoing in Canada, Mexico, the US, Bolivia, Brazil, Paraguay, and Belize and are mostly triggered by imported cases. “However, not all countries are experiencing sustained transmission, and we still have time to prevent it,” said Barbosa, who urged all countries to increase population coverage to 95% with two doses of the measles, mumps, and rubella vaccine to prevent community transmission of the virus.

An infected person can transmit measles through the respiratory route to 16-18 susceptible individuals. Referring to the virus, Barbosa commented that “it is perhaps the most virulent virus known to humankind,” adding that it is experiencing a global resurgence that has also triggered alarms in Europe and Australia.

The decline in vaccination rates, driven in part by antivaccine rhetoric, remains a key factor. The loss of measles-free status in the Americas “is an example of how damaging antivaccine fallacies are. Natural measles can be serious, leave long-term effects, and kill,” said Pablo Yedlin, MD, national deputy for Tucumán, and professor of public health at Universidad San Pablo-Tucumán, San Pablo, Argentina, on his social media account.

The concern now is that the US and Mexico could follow Canada if these countries do not halt endemic transmission before January and February 2026, 12 months since their first detected cases.

“I hope no other country will lose its status [of being free of endemic measles transmission]. We are working hard to support those countries and stop transmission before the 12-month deadline, thus preventing them from reaching the point of losing their certification,” said Barbosa.

Speaking to the Medscape Spanish Edition, Rodrigo Romero-Feregrino, MD, general coordinator of the Asociación Mexicana de Vacunología in Mexico said, “But the risk for that outcome in the US and Mexico “is very high. There are possibilities of avoiding the loss of certification, but it is necessary to take all the necessary actions correctly to stop the outbreaks.”

Salas noted that cases in the US began with outbreaks in Texas and New Mexico, although subsequent cases were reported in Utah, Arizona, and South Carolina.

The US Centers for Disease Control and Prevention documented 44 outbreaks in 2025, compared with 16 in 2024 and just over 1600 confirmed cases. Approximately 92% of the affected individuals were unvaccinated or had an unknown vaccination status.

“We continue to support the measures taken to control these outbreaks. We hope that the US can interrupt the spread as it did in the past, even when it was on the verge of losing its [measles-free] status,” said Salas.

However, the situation in Mexico is concerning. Chihuahua accounted for most early cases, and activity has since shifted to other states, including Jalisco and Guerrero, partly because of transmission among farmworkers, said Salas.

Mexico has reported just over 5000 confirmed cases in 2025 across 27 of its 32 states, ranking first in Latin America and ninth globally, although more than twice as many additional cases remain unconfirmed, according to El País, a leading national newspaper in Spain. 

“Mexico is doing important work to contain outbreaks, and a follow-up vaccination booster campaign will be launched in April 2026. However, the PAHO Regional Commission [for Monitoring and Verification of the Elimination of Measles, Rubella, and Congenital Rubella Syndrome] recommends that they do not wait until April and act now.” said Salas.

PAHO stated that it is facilitating access to vaccines through the Revolving Fund, strengthening epidemiological surveillance, training vaccination staff, and deploying a field mission this week in Chihuahua to support timely case detection and interrupt transmission, even before laboratory confirmation.

“It is essential to act to contain the current outbreaks with mass vaccination, early detection, and containment measures for cases and to plan a sustainable and long-term prevention programme to prevent this from happening again,” said Romero-Feregrino.

Three Keys

In his closing remarks, Barbosa outlined three priorities for countries aiming to eliminate measles.

The first is vaccination, with a high coverage of more than 95% receiving two doses and consistent uptake across communities, so that national averages do not hide pockets of unvaccinated groups. Second, a sensitive surveillance system that can detect imported cases should be established. Barbosa said, “It’s likely that in a country that [claims] it doesn’t receive imported cases, its surveillance won’t be very sensitive because it’s natural for them to arrive.”

The third priority is the rapid response capacity to interrupt transmission before infected individuals pass the virus to others. “Measles is so contagious that [if sustained transmission is established in a country] the challenge is tremendous,” he concluded.

Romero-Feregrino reported having no relevant conflicts of interest.

This story was translated from Medscape’s Spanish edition.