Measles – Region of the Americas

As of 18 April 2025, a total of 2318 measles cases, including three deaths, have been confirmed in six countries in the WHO Region of the Americas, an 11-fold increase compared to the same period in 2024. The majority of cases have occurred among people between 1 to 29 years, who are either unvaccinated or have an unknown vaccination status. Additionally, most cases are imported or linked to importation. Measles is a highly contagious, airborne viral disease that can lead to severe complications and death. Although it is preventable with two doses of the vaccine, over 22 million children worldwide did not receive their first dose of the vaccine in 2023. This has contributed to a global rise in measles cases in 2024, which heightens the risk of imported infections, particularly from unvaccinated travellers arriving from areas where the virus is actively circulating. WHO is working closely with countries in the WHO Region of the Americas to prevent the spread and reintroduction of measles. The regional risk is currently assessed as high, while the global risk remains moderate.

From 1 January to 18 April 2025, a total of 2318 measles cases, including three deaths, were confirmed in the WHO Region of the Americas, an 11-fold increase compared to the 205 cases of measles reported in the same period in 2024. The cases have been reported from six countries: Argentina (n= 21 cases), Belize (n= 2 cases), Brazil (n= 5 cases), Canada ^[1] (n=1069 cases), Mexico ^[2] (n= 421 cases including one death), and the United States of America ^[3] (n=800 cases, including two deaths).

Figure 1: Epidemic curve showing confirmed cases of measles in the Regions of the Americas, by week 1 January- 18 April 2025 (n = 2318)

 

Figure 2: Geographical distribution of the confirmed cases between 1 January- 18 April 2025

Overview by countries

Argentina

Between 1 January and 16 April 2025, Argentina reported 21 confirmed cases of measles; 10 in the Autonomous City of Buenos Aires and 11 in Buenos Aires Province. Of these, three cases were imported, 13 were identified as contacts linked to the imported cases, and five cases are still under investigation to determine their epidemiological link to the transmission chain.

The index case was reported on 31 January 2025, in a child with a history of international travel. The second case, another child and a contact of the index case, was reported on 3 February 2025. Neither of the two cases had a history of measles vaccination, and both were laboratory-confirmed by RT-PCR. Following these initial cases, 19 additional cases were confirmed up to 16 April, with ages ranging from 5 months to 40 years. Two of these cases had a documented history of international travel. Only two cases required hospitalization due to pneumonia; the remaining cases were managed on an outpatient basis and are recovering well. Twelve of the cases were confirmed at the National Reference Laboratory of INEI-ANLIS "Carlos G. Malbrán," with genotype B3 identified. One of the imported cases, associated with recent international travel to Thailand, was identified as genotype D8.

Belize

On 12 April 2025, the Belize Ministry of Health & Wellness confirmed two positive measles cases—Belize’s first since 1991. The cases involved 17-year-old males from the Corozal and Cayo districts with no vaccination history, who travelled to Chihuahua, México, from 5 January to 31 March 2025 to attend a religious gathering. The onset of symptoms occurred on 2 April and 3 April 2025. Blood samples and nasopharyngeal swabs were collected for both cases and confirmed positive for measles on 12 April 2025. Thirteen close contacts who attended the religious gathering in Chihuahua were interviewed by the Ministry of Health (MOH) team and monitored daily for signs and symptoms. Despite significant efforts to increase vaccination coverage, Belize remains below the target range of 92-95%.  In 2024, Belize reported a country percentage of 83.9% for the second dose of the MMR vaccine.

Brazil

Between 1 January and 18 April 2025, Brazil reported five confirmed cases of measles across four locations: Federal District (1), Rio de Janeiro (2), Rio Grande do Sul (1), and São Paulo (1). The two cases in Rio de Janeiro are children under one year of age, both without a history of vaccination. The onset of symptoms was on 28 February and 2 March, 2025. The cases in the Federal District (symptom onset 1 March 2025) and Rio Grande do Sul (symptom onset 6 April 2025) are adults with a history of international travel. Additionally, an adult case reported in São Paulo who has a history of vaccination, and no history of international travel was reported with symptom onset on 4 April 2025. The source of infection for this case is currently under investigation.     

Canada

Between 1 January and 12 April 2025, Canada reported 1069 confirmed and probable cases of measles from seven provinces: Alberta, British Columbia, Manitoba, Ontario, Prince Edward Island, Quebec, and Saskatchewan. These far exceed the 177 confirmed and probable cases reported in 2024, representing the highest annual case count since the country achieved measles elimination in 1998.

The majority (83%) of the cases reported in 2025 are linked to a large, multi-jurisdictional outbreak occurring among unvaccinated individuals in under-vaccinated communities that sometimes interact with one another.  Between 27 October 2024 and 12 April 2025, 971 cases have been reported in seven provinces. The outbreak was initiated by an internationally imported case that attended a large gathering in New Brunswick in October 2024, which included attendees from multiple provinces. Most cases associated with this outbreak are either unvaccinated (84%) or have unknown vaccination status (12%). To date, only a small number of outbreak-associated cases have occurred outside the initially affected under-vaccinated communities, with no evidence of significant further spread beyond these communities. 

Additionally, between 1 January and 12 April 2025, small numbers of localized outbreaks have been reported, consisting of two or more epidemiologically and/or virologically linked cases. These outbreaks are distinct from the multi-jurisdictional outbreak described above and have been directly related to internationally imported cases. During this same period, 16 measles cases in Canada have been attributed to international travel.

Mexico

Between 1 January and 16 April 2025, Mexico confirmed 421 measles cases: two imported, 35 import-related, and 384 under investigation. Cases were reported in Campeche (n= 4), Chihuahua (n= 403, including one death), Oaxaca (n= 4), Querétaro (n= 1), Sinaloa (n= 1), Sonora (n= 5), Tamaulipas (n= 2) and Zacatecas (n= 1).

The first confirmed case is an unvaccinated child in Oaxaca with a history of international travel between October 2024 and January 2025. The child arrived in Mexico on 29 January and developed symptoms on 10 February. On 14 February, the Oaxaca State Public Health Laboratory reported positive RT-PCR and IgM results for measles with genotype B3 identified. Three related cases were later confirmed.

On 20 February, the second confirmed case was reported in the State of Chihuahua in an unvaccinated child. The onset of symptoms was on 11 February, and measles was confirmed by the Chihuahua State Public Health Laboratory with positive RT-PCR and IgM results. The identified genotype was D8.  Following contact tracing and active case searches, 419 additional cases were identified.

The majority of cases were among those aged 25–44 years, accounting for 34.4% (n= 145), followed by children aged 5–9 years (13,5%, n= 57). In terms of vaccination history, 92.4% (n= 389) had no vaccination history, while 3.8% (n=16) had received one dose of the MMR vaccine, and another 3.8% (n=16) had received two doses.

United States of America

As of 17 April 2025, a total of 800 confirmed measles cases were reported by 25 jurisdictions: Alaska, Arkansas, California, Colorado, Florida, Georgia, Hawaii, Indiana, Kansas, Kentucky, Maryland, Michigan, Minnesota, New Jersey, New Mexico, New York State, New York City, Ohio, Oklahoma, Pennsylvania, Rhode Island, Tennessee, Texas (including two confirmed deaths), Vermont, and Washington. Of the total cases, 93% (n= 751) are associated with outbreaks (defined as three or more cases), with ten outbreaks identified so far this year. The outbreak in Texas, New Mexico, and Oklahoma accounts for 82% of the reported cases.

Children under the age of five accounted for 31% (n=249) of cases, individuals aged 5–19 for 38% (n=304), adults over 20 for 29% (n=231), and age was unknown for 2 % (n=16). The vast majority (96%) of the cases were unvaccinated or had unknown vaccination status, 1% had a single dose of the MMR vaccine, and 2% had received two doses. Hospitalization was required in 11% of total cases (n=85 of 800). Among children under five, 19% (47 of 249) required hospitalization. MMR vaccination coverage in children has decreased in recent years from 95.2% in 2019-2020 to 92.7% in 2023-2024.

Measles is a highly contagious acute viral disease that affects individuals of all ages and remains one of the leading causes of death among young children worldwide. The disease is airborne, transmitted through the air or via droplets from the nose, mouth, or throat of infected persons.

Initial symptoms, which usually appear 10-14 days after infection, include high fever, rash usually accompanied by a runny nose, bloodshot eyes, cough and tiny white spots inside the mouth. The rash appears 2-4 days after the onset of fever and spreads from the head to the trunk to the lower extremities. A person is infectious about four days before and up to four days after the rash appears. While there is no specific antiviral treatment for measles, most people recover within 2-3 weeks.

Measles is usually a mild or moderately severe disease. However, measles can lead to complications such as pneumonia, diarrhoea, secondary ear infection, inflammation of the brain (encephalitis), blindness, and death. Postinfectious encephalitis can occur approximately in about one in every 1000 infected persons. Measles also produces immune amnesia; a pathological process that makes the immune system forget how to protect against infections and leaves the infected individual more vulnerable to other infections.

The measles vaccine is one of the most effective vaccines available. A two-dose schedule is 97% effective in preventing measles for life.  

Following the declaration of measles elimination in the Americas Region in 2016, there was an unusual and consistent increase in confirmed cases of the disease from 2017 to 2019. In 2019, the region recorded its highest incidence rate at 21.5 cases per million population. This increase was largely due to large outbreaks in Venezuela and Brazil, which led to the reestablishment of endemic measles transmission and the loss of elimination status in these countries.  Between 2018 and 2023, the Americas Region reported 49 187 confirmed cases in 18 countries, resulting from the importation of viruses from other regions of the world and the resurgence of endemic transmission in Venezuela and Brazil.  The last endemic case of measles in the Americas Region was reported by Brazil in June 2022. By 2024, 465 confirmed cases were registered, all either imported or related to importation. That same year, the elimination of the endemic disease in the Americas Region was reverified.

Regional and National Public Health Authorities in the Americas Region are implementing public health measures to control the outbreak, and WHO is providing support by:

• Issuing epidemiological alerts and updates due to the increase in measles cases in several countries in the WHO Region of the Americas that started in 2024.
• Issuing the Public Health Risk Assessment related to measles in the region of the Americas, classified the risk as "High", especially in countries with low vaccination coverage.
• Continuing to monitor the situation and work closely with countries in the Region of the Americas to support their vaccination, surveillance and rapid outbreak response efforts to prevent the spread and reintroduction of measles and to protect the health of the entire population.
• Providing technical assistance and follow-up with laboratories in
  countries that have had cases/outbreaks.
• Strengthening countries’ rapid response capacities by 1) training healthcare workers in rapid response to outbreaks, using hybrid workshops and virtual courses; 2) providing financial funds for international consultants’ deployment in the most affected areas in LAC; 3) having virtual follow-up meetings with countries.
• Promoting mass follow-up vaccination campaigns in
  countries with highly susceptible populations to rapidly reduce the risk of the reintroduction of endemic measles and rubella in the countries of the Region.
• Enhancing risk communication and community engagement in countries where outbreaks have occurred, to reinforce their commitment to immunization and recommended actions.

In the WHO Region of the Americas, in 2025, there is an 11-fold increase in the number of cases compared to the same period in 2024. Although an improvement has been achieved in measles rubella surveillance indicators, there are still countries that do not meet the minimum notification rate of two suspected cases per 100 000 population, in addition to other indicators, in a homogeneous way. This could delay detection, notification, confirmation, and rapid response actions.

Difficulty in maintaining adequate levels of vaccination in the migrant population, vaccine-hesitant groups and other at-risk populations within the Region are big challenges. Given that several countries in Europe, Central Asia and Africa have areas of circulation of the virus, the identification of imported cases from these areas is expected. Intense migration from areas where the disease is endemic to areas where it is not could increase the risk of new outbreaks and cases. Considering population movement, international travel and mass gathering events, the risk of international spread cannot be ruled out. Travellers from regions with ongoing outbreaks can introduce the virus into countries with higher vaccination coverage, where there are still vulnerable populations, particularly infants who may not yet have received their first dose of the measles vaccine.

The overall risk of measles in the Americas Region is considered high due to several factors:

• Ongoing virus circulation from imported cases has led to outbreaks with extended transmission chains, secondary cases, and virus spread to new areas and countries in 2025.
• Suboptimal vaccination coverage persists across the region. In 2023, only 28.6% of countries achieved over 95% coverage for the first MMR dose (MMR1), and just 16.7% for the second dose (MMR2). Regional coverage was 87% for MMR1 and 76% for MMR2. Data for 2024 is still being consolidated.
• An increasing number of susceptible individuals due to continued low coverage, driven by factors like the COVID-19 pandemic, vaccine hesitancy, and limited access to healthcare, especially among vulnerable groups such as migrants, displaced persons, and Indigenous populations.

The overall risk of this event in the WHO Region of the Americas, especially in countries with low vaccination coverage, is classified as high with a high confidence level based on available information.

The overall risk at the global level is assessed as moderate due to the ongoing transmission in all the other WHO Regions, where immunization programs in several countries are not at an optimal level due to various factors, such as resource limitations, vaccine hesitancy, political instability, and health system weaknesses. These challenges have resulted in gaps in vaccination coverage, leading to widening pockets of the unvaccinated population and creating a pathway for measles to spread. This not only poses a public health concern for affected countries but also represents a potential risk for other regions due to international travel and population movement. The global risk of transmission remains a threat and particularly in areas with moderate or low vaccine coverage and could lead to new outbreaks in an unvaccinated population. This risk, coupled with gaps in laboratory systems and surveillance, outbreak detection and rapid response capacity, impedes progress towards global measles elimination goals and further exacerbates the threat of spread.

WHO recommends maintaining sustained homogeneous coverage of at least 95% with the first and second doses of the measles-containing vaccine (MCV) and strengthening integrated epidemiological surveillance of measles and rubella to achieve timely detection of all suspected cases in public and private healthcare facilities.

WHO recommends strengthening epidemiological surveillance and preparedness and rapid response capacities in high-traffic border areas to rapidly detect and respond to suspected measles cases. Providing a rapid response to imported measles cases to avoid the re-establishment of endemic transmission through the activation of rapid response teams trained for this purpose and by implementing rapid response protocols when there are imported cases. Once a rapid response team has been activated, continued coordination between the national, sub-national and local levels must be ensured, with continuous and effective communication channels across all levels. During outbreaks, it is recommended to establish adequate hospital case management and infection prevention and control capacity to avoid health care-associated infection transmission, with appropriate referral of patients to airborne infection isolation rooms (for any level of care) and avoiding contact with other patients in waiting rooms and/or other hospital rooms.

WHO recommends providing broad access to measles, mumps, and rubella (MMR) or measles and rubella (MR) vaccination to maintain high vaccination rates of the general population and to ensure individuals at high risk of exposure are up to date on this vaccination, such as health and care personnel and international travellers. Individuals living in outbreak areas should follow local public health guidance. Globally, between 2000 and 2023, vaccination successfully prevented an estimated 60 million deaths (6 million deaths in the Americas) and decreased an estimated measles death from 800 062 in 2000 to 107 500 in 2023, which is an 87% decrease.

WHO recommends maintaining a stock of the MR and/or MMR vaccines, and syringes/supplies for responding to imported cases. Facilitating access to vaccination services according to the national scheme to incoming and outgoing international travellers, including individuals due to perform activities, domestically or abroad, in areas with ongoing measles outbreaks, displaced populations, indigenous populations, or other vulnerable populations.

WHO advises international travellers to check and update their vaccination status against measles prior to departure. Unvaccinated individuals from areas experiencing measles outbreaks, with knowledge of exposure to measles cases and/or presenting signs and symptoms compatible with measles virus infection, should consult local health authorities before undertaking an international voyage. At present, no additional measures that significantly interfere with international traffic are warranted.

• World Health Organization. Measles Fact sheets. 
• Epidemiological Alert: Measles in the Region of the Americas, 28 February 2025. Washington, D.C: PAHO/WHO; 2025.
• Public Health Risk Assessment related to measles: implications for the Americas Region - 24 March 2025, PAHO/WHO. 
• Measles-Rubella bi Weekly Bulletin (13-14)- 5 April 2025. Washington, D.C.: PAHO/WHO; 2025.
• Centers for Disease Control and Prevention. Measles cases and outbreaks. Atlanta: CDC;2025.
• Public Health Agency of Canada (PHAC); Measles and rubella weekly monitoring report.
• Secretaría de Salud de México. Situación Epidemiológica de Enfermedades Prevenibles por vacunación.
• Ministerio de Salud de Argentina. Boletín Epidemiológico Nacional.
• Immunization throughout the life course in the Americas. Washington, D.C.: PAHO; 2025.
• Strategic Advisory Group (SAG) on Vaccine Preventable Diseases (VPD). Washington, D.C.: PAHO/WHO; 2024.
• Regional Framework for the Monitoring and Re-Verification of Measles, Rubella, and Congenital Rubella Syndrome Elimination in the Americas. Washington, D.C.: PAHO/WHO; 2024.
• World Health Organization. Health topics, Measles
• World Health Organization, Measles Outbreak Guide

^[1] The number measles cases by epiweek for Canada included confirmed and probable cases

^[2] The number measles cases by epiweek for Mexico were reported until EW14

^[3] The number measles cases by epiweek for the United States were reported until EW16

Citable reference: World Health Organization (28 April 2025). Disease Outbreak News; Measles in the Region of the Americas. Available at: https://www.who.int/emergencies/disease-outbreak-news/item/2025-DON565