This major setback in nearly three decades offers an uncomfortable lesson: measles elimination is not lost overnight; it erodes slowly.

This article by Obed Rosas originally appeared in the February 5, 2026 edition of Sin Embargo.

Mexico City, On February 20, 2025, the Chihuahua Health Department reported a case of measles in a 9-year-old boy from a Mennonite community in the municipality of Cuauhtémoc who had traveled to Seminole, Texas, a settlement where measles cases had already occurred with one known death at the time of the visit.

The boy’s school in Chihuahua was closed after more cases were detected. A month later, on March 20, the National Institute of Diagnosis and Reference (InDRE) confirmed that the virus isolated in the first patients belonged to the same lineage of measles previously identified in Seminole, Texas.

This is how Irma Leticia de Jesús Ruiz González, from the Chihuahua State Health Department, and Rubén Morales Marín, from the Autonomous University of Chihuahua, describe the reintroduction of measles in the state, in an article published last November in the American Journal of Field Epidemiology. The text warns that the outbreak occurred in “a highly susceptible population, such as the Mennonite community in Chihuahua, where there is low adherence to vaccination for religious or cultural reasons, in addition to close interconnection with other unvaccinated populations.”

Mennonites in Mexico

The outbreak occurred within an adverse regional context. In November 2015, the Pan American Health Organization (PAHO) declared that the Americas had once again lost their measles elimination status. The reintroduction of the virus led Mexico to face its largest outbreak since it interrupted endemic transmission in 1997. Chihuahua became the main epicenter of infections and deaths on the continent, with figures that even surpassed those of the entire United States.

This week, the Pan American Health Organization (PAHO) confirmed that Mexico leads the Americas in COVID-19 infections, with 6,428 cases and 24 deaths. Of that total, Chihuahua accounts for 4,495 cases and 21 deaths; followed by Jalisco, with 1,034 cases and one death; Chiapas, with 432 cases; Michoacán, with 261; and Guerrero, with 257.

Of the total infections, 275 were imported, 4,054 were related to importation, and 2,839 remain with the source of infection under study.

The report in the American Journal of Epidemiology highlights that 10 of the deaths occurred among Indigenous communities in Chihuahua, where 569 cases were recorded. Three deaths were recorded in the rest of the population, in addition to the death of a Wixárika child from Nayarit.

“The Rarámuri indigenous population of Chihuahua had a mortality rate 18 times higher than the rest of the population, and this excess was statistically significant,” the study notes. The age distribution shows especially high rates in children under six months and in infants aged six to 11 months, with levels 41.4 and 82.5 times higher, respectively, than those observed in people aged 50 and over. The second most affected group was the 20-39 age group.

In mid-January, another study conducted by researchers from the University of Guadalajara, with participation from the Tlajomulco de Zúñiga campus and the University Center of Los Altos, identified five key findings. The first: the outbreak was highly concentrated, with 73 percent of the cases in Chihuahua and 76.8 percent in just 45 municipalities.

The second finding was the existence of two independent introductions of the virus: one across the northern border and a separate importation into Oaxaca. Third, the analysis describes a three-stage transmission pattern: introduction through networks of temporary agricultural workers, amplification in under-vaccinated communities, and subsequent spread to marginalized Indigenous populations.

The fourth point highlights that vaccine effectiveness remained high, supporting the theory that the outbreak was due to an accumulation of susceptible individuals rather than vaccination failures. The fifth point identifies age, living conditions in indigenous communities, lack of vaccination, and residence in rural areas as independent risk factors.

The report also documents the concentration of the outbreak in closed communities with persistent immunity gaps, such as the Mennonites of Chihuahua, a pattern similar to that observed in the 2015 outbreak in Texas, which resulted in 762 cases and two deaths. Comparable episodes have been recorded in recent years in Orthodox Jewish communities in New York and Amish communities in Ohio, reinforcing the existence of “hotspots of susceptible individuals” capable of triggering large epidemics even in countries with seemingly high national coverage.

This resurgence is occurring within a complex regional context. In November 2025, the Pan American Health Organization (PAHO) warned that the Americas had once again lost their measles elimination status, just one year after regaining it. The combination of ongoing imports and inequalities in access to vaccination threatens to reestablish endemic transmission.

Although the study acknowledges limitations—such as self-reporting of vaccination status and the partial availability of genomic data—it is the most comprehensive epidemiological analysis conducted to date on a measles outbreak in Latin America. It integrates individual surveillance data, genetic information, and social determinants at the municipal level in all 32 states of the country.

The conclusion is stark: measles did not return due to vaccine ineffectiveness, but rather due to the accumulated neglect of entire communities. Without targeted campaigns, strengthened molecular surveillance, and specific strategies for mobile, Indigenous, and rural populations, Mexico will remain vulnerable to new outbreaks. This major setback in nearly three decades offers an uncomfortable lesson: measles elimination is not lost overnight; it erodes slowly.

The post A Child with Measles Arrived in Mexico from the US, & Then the Virus Was Everywhere appeared first on Mexico Solidarity Media.

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