The rapid spread of measles is not just affecting the U.S. — it is expanding worldwide, including Europe. Any international travel can lead to a measles exposure, so it is critical to ensure you are immune to measles before you travel. If you were immunized in the state of Arizona, the Arizona Department of Health Services provides immunizations records electronically through MyIR. Register and request your immunization records through the ADHS website.
Learn more about global measles outbreaks.
The Health Observatory works closely with researchers across Arizona’s universities and public health departments to better understand the virus and bring reliable health information to all Arizonans.
Members of the Health Observatory have more than 100 years of combined expertise in public health work, including predictive modeling of infectious diseases. The team is composed of current and former public health professionals, epidemiologists, mathematicians and data modelers.
History of measles in the United States
Though records of measles stretch back through history, measles first became a nationally notifiable disease in the United States in 1912. That meant that health care providers and laboratories were required to report all diagnosed cases. In the first 10 years of reporting, there were an average of 6,000 measles-related deaths each year.
In 1963, there were 385,156 reported measles cases in the United States. That same year, the first measles vaccine was developed and licensed for public use in the country. This led to a precipitous drop in cases, with only 22,231 reported cases in 1968, when an improved vaccine with less severe side effects followed.
In 1978, the CDC set out to eliminate the disease from the U.S. in four years. Though the goal wasn’t met, this campaign brought cases to well below 10,000 a year for most of the 1980s. However, 1989 saw 17,914 cases and an outbreak among vaccinated children, prompting the recommendation of a second dose of the MMR vaccine.
In 2000, the United States reached a momentous achievement in the fight against disease: endemic measles was declared eliminated. This meant the disease did not continuously spread for more than a year. This achievement was due to the highly effective vaccination program, which included school requirements for the MMR vaccine in the United States, as well as better measles control in the Americas region.
Since 2000, there have been numerous outbreaks of measles in the United States and Arizona. 2008 saw 140 cases in Pima county and there were 86 reported cases in an U.S. Immigration and Customs Enforcement detention facility in Pinal county.
In 2019, more than 1,200 cases were reported in 31 states, largely among unvaccinated people. It was the largest outbreak since 1992, and cost the U.S. its measles elimination status. The most recent outbreak began in Texas in January 2025 is the largest measles outbreak since 2000 with nearly 1,500 reported cases. This outbreak also resulted in the first pediatric measles death in 22 years.
Stay up-to-date on current cases of measles and other infectious diseases in Arizona.
Herd immunity and measles
Herd immunity is when a disease cannot spread through a population because enough people are immune to it, either through vaccination or exposure. The percentage of immune people needed to reach herd immunity varies by disease and the threshold for herd immunity for measles is particularly high — 95% of the population — because it is so infectious.
Since 2015, the United States has only met that high herd immunity threshold for measles three times — in 2017, 2018 and 2020. Since 2020, the nation’s herd immunity has been on a downward trend, with the lowest percentage — 92.5% — in the last decade coinciding with the largest measles outbreak in that same time period.
Measles and international travel
Although measles was declared eliminated in the United States in 2000, measles cases and outbreaks continue to occur in the United States due to unvaccinated international travelers. Large measles outbreaks are possible when travel-related measles cases reach at-risk U.S. populations with low immunization against measles. In 2019, the U.S. nearly lost its elimination status with almost 1,300 measles cases from a large outbreak in New York and cases in 30 additional states. After a decrease in global measles incidence during the COVID-19 pandemic, global and U.S. measles activity continues to rise.
Right now, measles outbreaks are happening in every region of the world. Anyone who is not protected against measles can get measles while abroad and easily spread it to others when they return home. Per the CDC, all international travellers who do not have immunity to measles should get two doses of MMR vaccine at least two weeks before travelling internationally.
Learn more about protecting yourself from measles when you travel.
Measles cases and outbreaks
Visit the CDC website for a detailed epi-curve of measles outbreaks in the U.S.
Content curated by Dr. Rebecca Sunenshine, Medical Director of Arizona State University’s Health Observatory. Visuals created by Meaghan Batchelor.
Content on these webpages is intended for general knowledge and informational purposes only, and does not constitute medical advice. If you think you have signs or symptoms of measles or been exposed to someone with measles, please see a health care provider.
Get critical updates
Stay informed about measles updates and how to protect yourself.