Worldwide, measles is increasing in the United States, Canada, Mexico, South America and parts of Europe. In 2025, North and South America registered 11 times more cases than during the same period of the previous year. In Europe, measles rates reached their highest level in 25 years.
In the United States, as of May 2, 2025, the health authorities had confirmed 935 measles cases affected by 30 states. This is a considerable increase compared to the 285 cases notified in 2024. There is also a large outbreak of measles in Canada, with more than 1,000 cases.
The conversation asked Rebecca Schein, a specialist in pediatric infectious diseases, to explain what this increase, both nationally and internationally, could mean, for a disease that was declared eradicated in the United States in 2000.
How do this year’s measles cases compare with those of previous years?
Between 2000 and 2010, less than 100 cases of measles were reported per year in the US since 2010, isolated outbreaks were recorded, mainly in non -vaccinated communities, with approximately 200 and 300 cases a year. The last important outbreak in the US occurred in 2019, with 1,274 cases, mainly in the metropolitan area of New York City and parts of New Jersey.
The cases decreased between 2020 and 2023 during the COVI-19 Pandemia, returning to the prepazed levels in 2024. Currently, most cases in the US come from an epidemic in Texas, with 702 cases confirmed until May 6. Of these, 91 people were hospitalized and three, two of them children, died. Measles of measles are still reported. Texas is one of the 12 documented measles outbreaks in the US from 2025 to date.
The World Health Organization has declared that North and South America have a high risk of measles. Canada reported a total of 1177 cases until April 19, of which 951 are related to an outbreak that began in New Brunswick in October 2024 and extended to seven provinces. In 2023, 12 measles cases were recorded throughout Canada.
Mexico reported 421 confirmed measles cases until April 18, and another 384 cases are under investigation. There are also small measles outbreaks in South America, where Belize reported its first two cases since 1991. Brazil reported five cases, and in Argentina there are 21 confirmed measles cases, mainly in the capital, Buenos Aires.
In Europe, measles cases multiplied by ten, reaching 35 212 in 2024, according to the European Center for Disease Prevention and Control.
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How did measles eliminated the United States?
Measles is one of the most contagious infections ever identified. A person with measles can spread the infection between 12 and 18 more people. This figure, that the epidemiologists call R0, is 1 to 4 for the flu and 2 to 5 for the COVID-19.
In 1912, measles became a nationwide statement disease, monitored by all US health departments at that time, were recorded between 3 and 4 million cases and 6,000 deaths a year in the country. Medical care improved and the mortality rate decreased, but the cases were fired to epidemic levels every two or three years.
It was not until 1963, when the first measles vaccine was generalized, that the cases decreased dramatically. The current measles vaccine, called Triple Viral (MMR), since it also includes vaccines against papers and rubella, launched into the market in 1971. In 1977, the US government launched the National Inmunization Initiative of Children’s Immunization to ensure that school -age children received the vaccine against polio, diphtheria, people’s cough, tetanas, papers, spillage, rubella and measles.
Vaccination rates in children who began primary school increased to 96 % in 1981. As of 1993, the children’s vaccine program helped to ensure that all children could receive vaccines, regardless of their ability to pay.
The vaccination programs were a resounding success. By 2000, measles cases in the US had been reduced to zero, and infections occurred only in people traveling abroad. That year, the centers for disease control and prevention declared measles eradication in the country.
Why is the increase in measles rates so worrying and how can it be prevented?
Measles is a virus, like the common cold. Unlike bacterial infections, which can be treated with antibiotics, viral infections are not usually treatable, but they can often be prevented by vaccination programs.
Vaccination stimulates the immune system to produce antibodies that fight a specific infection. For most people, a single dose of the measles vaccine protects them from infection. The second dose helps guarantee long -term protection. Measles is so contagious that 95 % of the population must be vaccinated to protect the community, a concept called group immunity.
However, during the last 20 years, vaccination rates have decreased worldwide, with a fall specially pronounced during pandemic due to limited medical care. In line with this trend, cases of measles in the US. Have been increasing. As a result, some experts in infectious diseases fear that measles is becoming a common infection again.
What happens if measles rates continue to increase?
Public health authorities define endemic infections such as those that are constantly presented in a region. For example, the common cold and now the COVID-19 are endemic in the US.
A number of cases higher than normal in an area is called the outbreak. In the case of measles, an outbreak is defined as more than three cases in a local county or area. When the cases of an outbreak spread outside the local area, it is an epidemic, and if an epidemic extends to many countries of the world, it becomes a pandemic.
The measles outbreak in Texas began in January 2025 as an outbreak in six counties and quickly reached epidemic levels, affecting a total of 29 counties and counting 702 cases until May 6.
A 2022 study used a computer algorithm to model the trajectory of measles cases in the US, given the decrease in vaccination rates during pandemic. If children who did not receive vaccines due to the pandemic do not receive reinforcement vaccines, and the reticence to be vaccinated continues to the current rhythm, according to the study, 21% of US children (about 15 million) will be vulnerable to measles in the next five years. This figure is well below that necessary to prevent measles outbreaks.
A study with a similar approach, published in April 2025, concluded that measles is likely to be endemic in the US and predicted that the country could record 850,000 cases in the next 25 years if vaccination rates remain stable. If vaccination rates continue to decrease, according to the study, the number of cases could increase to 11 million in the next 25 years.
What would be needed to reverse the increase in cases?
To reverse this trend it will be necessary to constantly increase community vaccination rates. The study of April 2025 concluded that increasing community vaccination rates by 5% would stop the increase in cases to between 3,000 and 19,000 in the next 25 years.
Another epidemiological model that estimates the propagation of measles, published in February, predicted that, when intervening early in an outbreak with the support of local health departments, measles outbreaks can be contained whenever 85% of the population is vaccinated against the disease.
This, of course, requires guaranteeing continuous access to free and accessible children’s vaccines, as well as restoring public confidence in measles vaccines.
*Rebecca Schein is an attached professor for infectious disease pediatrics at Michigan State University
This article was originally published in The Conversation
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