Tracking measles cases in the United States

CNN
 — 

Several outbreaks of measles in the United States are driving case counts up and raising alarm among public health officials, especially as vaccination rates among children lag.

By the end of March, there were already more reported cases in 2024 than there were in all of 2023, according to data from the US Centers for Disease Control and Prevention.

Measles is a highly contagious airborne disease. It can cause serious health consequences or death, especially for young and unvaccinated children.

General symptoms may include fever, cough, runny nose, watery eyes and a rash of red spots. About 1 in 5 unvaccinated people in the US who get measles will be hospitalized, according to the CDC. About 1 in every 20 children will develop pneumonia, and others may develop a dangerous swelling in the brain called encephalitis. Up to 3 of every 1,000 children who become infected with measles may die from respiratory and neurologic complications.

But measles is preventable, thanks to a highly effective vaccine. Experts recommend that children get the measles, mumps and rubella, or MMR, vaccine in two doses: the first between 12 months and 15 months of age, and a second between 4 and 6 years old. One dose is about 93% effective at preventing measles infection; two doses are about 97% effective.

The increase in measles cases this year can be attributed to falling vaccination rates and to increased travel, which can result in unvaccinated people acquiring measles abroad and bringing it back to the US, according to the CDC.

Measles was eliminated in the US in 2000. Imported cases are expected, but when vaccination rates are high, the risk remains low and outbreaks are rare. Outbreaks in 2019, particularly two in underimmunized Orthodox Jewish communities in New York, threatened measles elimination status in the US.

“If a measles outbreak continues for a year or more, the United States could lose its measles elimination status,” according to the CDC.

Because measles is so contagious, a high level of vaccination coverage is key to minimizing spread. The US has set a target vaccination rate of 95%, but coverage among kindergarteners has dipped below that in recent years. In the 2022-23 school year, just 93.1% of kindergarteners in the US had completed their MMR vaccine series, leaving about 250,000 at risk. Coverage varies widely by state and community.

Vaccine coverage has dropped in 41 states since the 2019-20 school year – the last school year with children vaccinated before the Covid-19 pandemic and the last year the nation met the CDC’s 95% coverage target.

Twenty states matched or exceeded 95% in the 2019-20 school year, when the national coverage rate was 95.2%. Only 13 states met the CDC’s goal during the 2022-23 school year, when national coverage sank to 93.1%.