Share on Pinterest- A surge in measles cases is threatening the US’s elimination status of the disease.
- Cases in 2024 are drastically outpacing previous years.
- Experts say that vaccination levels have fallen although they remain paramount to the national prevention strategy.
A surge in measles cases is threatening the United States’ elimination status, which it has held for more than 20 years.
The US has experienced 338 reported cases of measles between January 1, 2020 and March 28, 2024, according to the CDC. Nearly one-third of those cases (29%) occurred during the first quarter of 2024, representing a 17-fold increase over the average number of cases reported during the same time period between 2020-2023.
Measles is a viral infection that affects the respiratory system and causes a distinct rash. The disease is also highly contagious.
The United States declared endemic cases of measles eliminated in 2000, but the growing number of cases could upend two decades of public health strategy. Rates of measles vaccination have been steadily declining for years.
Susan Hassig, DrPH, MPH, an Associate Professor Emerita at the School of Public Health and Tropical Medicine at Tulane University, told Healthline that the CDC’s report is, “A very clear warning that we need to pay a bit more attention to measles vaccination.”
Hassig did not work on the report.
The lead author of the report, Adria D. Mathis, MSPH, who works in the Division of Viral Diseases at the National Center for Immunization and Respiratory Diseases of the CDC, told Healthline, “While the risk for measles for the majority of the U.S. population still remains low, it’s crucial that we take the necessary steps now in order to prevent the continued spread of measles and maintain elimination in the US.”
Two out of three measles cases occurred in unvaccinated individuals
Of the 338 reported cases of measles in the CDC’s report, the vast majority occurred in individuals who were unvaccinated or of unknown vaccination status. In total these two groups accounted for 91% of all reported measles cases. More specifically, unvaccinated individuals represented 68% of all cases, while those of unknown vaccination status represented 29%.
Only 9% of measles cases involved an individual who reported having one or more MMR vaccines. However, in 84% of cases the individual was eligible for vaccination.
“Almost all [cases] were in people who were unvaccinated or whose vaccination status was unknown. These findings underscore the need for additional efforts to increase measles, mumps, and rubella (MMR) vaccination coverage, especially among close-knit and undervaccinated communities,” said Mathis.
Besides vaccination status, international travel was also a predominant factor in US measles cases. Nearly all reported cases of measles (96%) were associated with traveling internationally or being around someone who had recently traveled. These cases highlight the need for vaccinations in all individuals who are traveling internationally.
The regions of Africa and the Eastern Mediterranean were the most common geographic areas associated with the importation of measles, according to the CDC.
“With outbreaks occurring in Europe and Africa, travelers are at risk for catching measles if they are under-vaccinated or unvaccinated,” Meghan Brett, MD, a Hospital Epidemiologist and Associate Professor of Infectious Diseases at UNM Health Sciences, told Healthline.
Elimination status threatened
The United States declared endemic measles eliminated in the year 2000, but that declaration is being threatened.
Endemic refers to when a disease is consistently present and regularly spread within a given region. So, the elimination of endemic measles means that while cases may still pop up in the US, they are not present with any regularity and are typically tied to a specific incident, such as international travel, that imports the disease.
Elimination status is a specific designation given only after certain conditions related to transmission of a disease are met.
According to the WHO, measles elimination is defined as, “the absence of endemic measles virus transmission in a defined geographical area (e.g. region or country) for at least 12 months in the presence of a surveillance system that has been verified to be performing well.”
As of 2023, the US has maintained its elimination status.
“However, the rapid increase in the number of reported measles cases observed in the first quarter of 2024 does represent a renewed threat to the U.S. elimination status. Maintaining high national and local MMR vaccination coverage remains central to sustaining measles elimination,” said Mathis.
US elimination status was previously threatened in 2019, following a series of outbreaks in New York state.
“We have done such good work eliminating measles that many of us have lived without seeing or experiencing the day-to-day and lifetime risks of measles infections. That often makes it harder to explain why vaccination is so important,” said Brett.
Who is at risk of measles?
While the vast majority of Americans are not at high risk of measles, and transmission remains low, some groups, especially small children, are susceptible to the disease.
“In public health, we think about protecting the most vulnerable in a population. And for measles it’s kids under the age of 12 months because we don’t routinely vaccinate under 12 months,” said Hassig.
The CDC recommends two doses of MMR vaccine for children. The first is administered between 12-15 months of age, and the second between the ages of four and six.
In addition to young children, anyone planning on international travel should also ensure that their measles vaccinations are current.
After returning from abroad, travelers should watch for the signs of measles, including:
- High fever
- Cough
- Runny nose
- Red, watery eyes
- Rash
“The key things families and parents can do to keep themselves safe are making sure you are all up to date with your measles vaccination. This is incredibly important before traveling since so many cases are happening in many parts of the world. And if you do develop symptoms that fit with measles after travel, it’s important to get tested early to limit the spread of the infection,” said Brett.
The bottom line
A surge in reported measles cases in the first quarter of 2024 is threatening the elimination status of the disease in the U.S.
Almost all cases of measles have been linked to unvaccinated individuals or those of unknown vaccination status.
International travel is also a predominant factor in new cases of measles, with 96% of cases associated with international travel.
Experts reiterate that measles vaccination is still the most important part of measles prevention and that young children and those traveling internationally should be up to date with vaccination.
