The cases have tripled since last year.
Measles cases in the U.S. have surged this year, with reported outbreaks and overall numbers through July already surpassing the total cases recorded in all of 2023. According to the latest data from the Centers for Disease Control and Prevention (CDC), there have been 188 reported cases across 25 states, New York City, and the District of Columbia as of July 25. This figure is more than three times the 58 cases reported for the entire previous year.
Of the reported cases, 43% involve children under five years old, and 32% are in individuals aged 20 and older. The majority of these cases—about 95%—involve individuals who were unvaccinated, had an unknown vaccination status, or had received only one dose of the measles, mumps, and rubella (MMR) vaccine. The MMR vaccine is approximately 93% effective against measles with one dose and 97% effective with two doses.
There have been 13 measles outbreaks this year, each involving three or more cases, compared to just four outbreaks in 2023. Nearly two-thirds of this year’s cases are linked to these outbreaks, with the largest occurring at a migrant shelter in Chicago in March, resulting in 57 cases. The outbreak in Chicago was declared over on May 30 after a 42-day period without new cases.
Measles is extremely contagious, potentially infecting up to 90% of unprotected individuals exposed to the virus. Symptoms typically appear 7 to 14 days after exposure and include high fever and a rash. The disease can lead to severe complications such as pneumonia, brain swelling, and death. Although measles was declared eliminated in the U.S. in 2000 due to successful vaccination efforts, recent declines in vaccination rates and increased global cases have led to periodic spikes. Notably, there were 382 cases across 28 jurisdictions in 2018 and 1,274 cases across 31 states in 2019, the highest number since 1992.
High-risk areas for measles exposure include airports where international travelers arrive. Recently, the Los Angeles County Department of Public Health confirmed a measles case in an individual who arrived at Los Angeles International Airport on July 26 from an international flight.
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