Experts emphasize that vaccination levels have declined, despite their critical importance to the national prevention strategy. This surge in measles cases poses a threat to the United States' elimination status, a status it has maintained for over 20 years.
Between January 1, 2020, and March 28, 2024, the United States has recorded 338 reported cases of measles, as per the CDCTrusted Source. Alarmingly, nearly one-third of these cases (29%) occurred during the first quarter of 2024, marking a 17-fold increase compared to the average number of cases reported during the same period between 2020 and 2023.
Measles is a viral infection that primarily impacts the respiratory system and is characterized by a distinctive rash. This disease is notorious for its high level of contagiousness.
The United States declared endemic cases of measles eliminated in 2000, marking a significant achievement in public health. However, the recent surge in cases threatens to undo two decades of progress in combating the disease. Compounding this issue, rates of measles vaccination have been steadily declining for years, contributing to the resurgence of the disease.
Susan Hassig, DrPH, MPH, an Associate Professor Emerita at the School of Public Health and Tropical Medicine at Tulane University, emphasized to Healthline that the CDC's report serves as "A very clear warning that we need to pay a bit more attention to measles vaccination."
Hassig was not involved in the report.
Adria D. Mathis, MSPH, the lead author of the report and a member of the Division of Viral Diseases at the National Center for Immunization and Respiratory Diseases of the CDC, emphasized to 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."
According to the CDC's report, two out of three measles cases occurred in individuals who were either unvaccinated or had an unknown vaccination status. Specifically, these two groups collectively comprised 91% of all reported measles cases. Among them, unvaccinated individuals accounted for 68% of the cases, while those with unknown vaccination status represented 29%.
Only 9% of measles cases involved an individual who reported having received one or more doses of the MMR vaccine. 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," emphasized Mathis.
In addition to vaccination status, international travel emerged as a significant factor in US measles cases. Nearly all reported cases of measles (96%) were linked to international travel or exposure to individuals who had recently traveled internationally. These cases underscore the importance of ensuring vaccinations for all individuals who plan to travel internationally.
According to the CDC, the regions of Africa and the Eastern Mediterranean were the most frequently implicated geographic areas associated with the importation of measles cases.
"With outbreaks occurring in Europe and Africa, travelers face an increased risk of contracting measles if they are either under-vaccinated or unvaccinated," Meghan Brett, MD, a Hospital Epidemiologist and Associate Professor of Infectious Diseases at UNM Health Sciences, warned in an interview with Healthline.
The United States declared measles eliminated as an endemic disease in the year 2000, but this status is now under threat.
Correct, "endemic" refers to a disease that is consistently present and regularly spreads within a given region. Therefore, the elimination of endemic measles in the United States means that while cases may occasionally occur, they are not present with any regularity and are typically linked to specific incidents, such as international travel, that introduce the disease into the country.
Correct, elimination status is a specific designation awarded when certain conditions related to the transmission of a disease are achieved.
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 United States has successfully 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," emphasized Mathis.
"We have made significant progress in eliminating measles, to the point where many of us have not experienced or witnessed the day-to-day and long-term risks associated with measles infections. This can sometimes make it challenging to convey the importance of vaccination," remarked Brett.
While the majority of Americans are not at high risk of measles, and transmission remains low, certain groups, particularly small children, are more susceptible to the disease.
"In public health, our focus is on safeguarding the most vulnerable members of the population. When it comes to measles, this includes children under the age of 12 months because routine vaccination typically begins after this age," explained Hassig.
The CDC recommends two doses of the MMR vaccine for children. The first dose is typically administered between 12-15 months of age, and the second dose is given between the ages of four and six.
In addition to young children, individuals planning international travel should ensure that their measles vaccinations are up to date.
After returning from abroad, travelers should be vigilant for signs of measles, including:
High fever Cough Runny nose Red, watery eyes Rash
"The key steps families and parents can take to stay safe include ensuring everyone is up to date with their measles vaccination. This is particularly crucial before traveling, given the prevalence of measles cases in many parts of the world. If you develop symptoms consistent with measles after traveling, it's important to seek testing early to minimize the spread of the infection," emphasized Brett.
The surge in reported measles cases in the first quarter of 2024 poses a threat to the elimination status of the disease in the U.S.
Nearly all cases of measles have been linked to individuals who are either unvaccinated or have an unknown vaccination status.
International travel plays a significant role in new cases of measles, with 96% of cases associated with travel abroad.
Experts emphasize that measles vaccination remains the most crucial aspect of measles prevention, and it is essential for young children and individuals traveling internationally to ensure they are up to date with their vaccinations.