Measles Cases in the US Increased Significantly in 2024

Brian Nowosielski;

Measles Cases in the US Increased Significantly in 2024

April 12, 2024

By Brian Nowosielski

News

Article

Drug Topics JournalDrug Topics May 2024

Volume 168

Issue 04

Since a 2019 measles outbreak, the CDC has seen an increasing number of cases in the US.

A recent spike in measles cases has threatened the elimination status of the disease in the US, prompting the CDC to continue vaccination initiatives across the country.

“Measles is a highly infectious febrile rash illness,” wrote the CDC in a recent report.¹ A measles rash “usually begins as flat red spots that appear on the face at the hairline and spread downward to the neck, trunk, arms, legs, and feet,” they wrote in their official measles overview.²

Although the disease was declared eliminated in the US in 2000, a 2019 outbreak in the northeastern part of the country has led to an alarming uptick in the number of cases, with 29% of cases from 2020 until now occurring in the first quarter of 2024.¹

In 2024 alone, 97 measles cases have been reported in the US | image credit: jarun011 / stock.adobe.com

What’s the Issue?

Measles importations in the US have threatened a disease that was once deemed eliminated. Despite a jump in cases from 2020 to 2023, elimination status was maintained, until recent spikes in 2024 have threatened that status.

In 2024 alone, 97 measles cases have been reported in the US, representing a 1700% increase from the mean average of the first quarter of 2020 to 2023.¹ And since publication of the CDC report at the end of March, cases in 2024 have reached over 100.³
Of the 338 cases reported in the last 4 years, 96% were associated with an importation. Of those 326 imported cases, 200 occurred in individuals who were unvaccinated or who had an unknown vaccination status.¹
The CDC reported transmission data on measles outbreaks in the past 4 years. Twenty measles outbreaks were reported from the start of 2020 until now. Of the 20 outbreaks, 7 occurred in 2024 alone, with a median outbreak size of 6 cases and a range of 3 to 86 cases per outbreak.¹

Why it Matters

A measles vaccine has been available since 1963. However, imported outbreaks and unvaccinated individuals have led to difficulties in controlling the disease’s elimination status.²

The CDC defines a disease as eliminated if there are no transmissions for 1 continuous year.² From 2000 to 2020, elimination status was maintained, but has since jumped due to several imported outbreaks in unvaccinated individuals.
From 2020 until now, 93 measles cases were directly imported from other countries, with 37% occurring in foreign visitors and 63% in US citizens. Furthermore, 90% of the directly imported cases occurred in individuals who were eligible for vaccination but did not receive it, or their status was unknown.¹
The jump in US measles cases, reported the CDC, is directly associated with a slew of outbreaks across the country. In 2021, 47 of 49 cases occurred in Afghan evacuees housed in US military sites. In 2022, 71% of cases were associated with an outbreak in central Ohio. And finally in 2023, almost half (48%) of all measles cases were associated with 4 different outbreaks around the country.¹

Expert Commentary

“What was surprising about 2024 is that we've seen a significant increase. It's an alarming number because it indicates a trend going in the wrong direction for us, a virus that we have successfully controlled, a virus that we successfully have an effective vaccine for. We're seeing a rise that is unfortunate, and actually preventable, and so this outbreak highlights the fact that we are not unfortunately done with measles,” John Brownstein, MD, PhD, epidemiologist and chief innovation officer at Boston Children's Hospital, told ABC News.⁴
“Risk for widespread US measles transmission remains low because of high population immunity,” said Adria Mathis from the CDC's Division of Viral Diseases.³ “However, because of the increase in cases during the first quarter of 2024, additional activities are needed to increase US routine measles, mumps, and rubella vaccination coverage, especially among close-knit and under-vaccinated communities. These activities include encouraging vaccination before international travel and rapidly investigating suspected measles cases.”
Paul Offit, MD, director of the Vaccine Education Center at the Children’s Hospital of Philadelphia, discussed the dangers of individuals remaining unvaccinated for the measles. “Number one is to find out what it is that's causing them to choose not to vaccinate, what's the fear, because the fear can invariably be addressed with information,” Offit told ABC News.⁴ “I think it's understandable how people can be hesitant to get a vaccine, but it is a dangerous game we play. I mean, it's a game of Russian roulette.”

In Depth Insights

With the elimination status of the measles threatened yet again, the CDC is working to inform the public on the growing issue and encourage vaccinations.

Of all the measles cases reported in the past 4 years, 309 patients were unvaccinated, representing 68% of all cases. Among all unvaccinated patients, 84% were eligible for a vaccine but did not receive it. Among 155 patients hospitalized within that timeframe, 92% of individuals were unvaccinated.¹
Measles outbreaks are not just prominent in the US, but globally as well. “During November 2022-October 2023, the number of countries reporting large or disruptive outbreaks increased by 123%, from 22 to 49,” wrote the CDC.¹ “Global estimates suggest that first-dose measles vaccination coverage had declined from 86% in 2019 to 83% in 2022, leaving almost 22 million children aged <1 year susceptible to measles.”