CDC warns measles outbreak threatening US elimination status

The Centers for Disease Control and Prevention (CDC) is calling for action to increase U.S. measles immunization amid a rise in cases that could threaten the nation’s status as one where the virus is eliminated.

The number of measles cases detected in 2024 has already nearly reached double the total confirmed in 2023. The CDC has confirmed 113 cases so far, compared to 58 detected last year.

The most recent Morbidity and Mortality Weekly Report from the CDC noted that 97 percent of U.S. measles cases since 2020 have occurred in the first quarter of this year. This rate represents “more than seventeenfold increase over the mean number of cases reported during the first quarter of 2020–2023.”

Overall, 91 percent of measles patients since 2020 have been unvaccinated or had an unknown vaccination status. Across all these cases, 96 percent were associated with international travel, while the remaining 4 percent had an unknown source.

The CDC noted that the U.S. was able to maintain its elimination status through the end of 2023 thanks to the “absence of sustained measles virus transmission for 12 consecutive months in the presence of a well-performing surveillance system.”

“However, because of the increase in cases during the first quarter of 2024, additional activities are needed to increase U.S. routine measles, mumps, and rubella vaccination coverage, especially among close-knit and undervaccinated communities,” the report stated. “These activities include encouraging vaccination before international travel and rapidly investigating suspected measles cases.”

Experts have expressed concerns that the increase in measles cases across the U.S. could be part of a worrying trend.

“I think there is concern that this trend will continue and that we will see more cases. It is early, but I think it is cause for concern,” Sarah Lim, an infectious disease physician and member of the Infectious Diseases Society of America, previously told The Hill.

The U.S. has a “Healthy People 2030” goal of maintaining a measles, mumps and rubella (MMR) vaccination rate of 95 percent by 2030. The most recent data found that kindergarteners have an MMR immunization rate of 93 percent. The U.S. has fallen off this goal for the past three years.

“The U.S. measles elimination status will continue to be threatened by global increases in measles incidence and decreases in global, national, and local measles vaccination coverage,” the CDC said.

“Because of high population immunity, the risk of widespread measles transmission in the United States remains low; however, efforts are needed to increase routine MMR vaccination coverage, encourage vaccination before international travel, identify communities at risk for measles transmission, and rapidly investigate suspected measles cases to maintain elimination.”