U.S. Measles Cases Are Rising in 2024, CDC Warns

In the 1950s, an estimated three million to four million Americans were infected with the measles virus each year, resulting in 400 to 500 deaths and 48,000 hospitalizations annually. But since the first measles vaccine was developed in 1963, case numbers fell dramatically—and measles was declared eliminated in the United States in 2000. During the 21st century, the nation has clocked several years with fewer than 100 cases of measles.

But now, in the first quarter of 2024, the number of measles cases recorded in the U.S. was significantly higher than in recent years, according to a new report from the Centers for Disease Control and Prevention (CDC).

Americans have reported a total of 338 cases since January 1, 2020—and 97 cases, or 29 percent of the total, came between the start of 2024 and March 28, per the report. And as of April 11, the number of cases in 2024 had risen to 121.

“What was surprising about 2024 is that we’ve seen a significant increase,” John Brownstein, an epidemiologist at Boston Children’s Hospital, tells ABC News’ Mary Kekatos. “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.”

Measles continues to be considered eliminated in the U.S., meaning there hasn’t been a sustained transmission chain lasting 12 consecutive months—the longest chain between 2020 and 2023 lasted 63 days. And the high level of immunity from vaccines means the risk for widespread transmission is low.

“However, the rapid increase in the number of reported measles cases during the first quarter of 2024 represents a renewed threat to elimination,” the authors write.

To prevent the spread of measles, the nation needs to maintain high levels of measles vaccine coverage, and undervaccinated communities should get immunized, the report says. More than 90 percent of people infected since the start of 2020 were either unvaccinated or had an unknown vaccination status.

“I think that people need to remember that this is a preventable disease,” Susan Hassig, an infectious disease researcher at Tulane University, says to Devi Shastri and Mike Stobbe of the Associated Press (AP). “It is a potentially dangerous disease for their children.”

Measles is a highly contagious virus, and its symptoms include high fever, cough, runny nose, red and watery eyes and a rash of small red spots. It can cause serious health complications, which young children are more likely to experience, such as pneumonia and inflammation of the brain. Around one in five unvaccinated people who get measles are hospitalized, and around one to three of every 1,000 infected children die from respiratory or neurological complications.

The virus spreads through the air when an infected person coughs or sneezes, and if nearby people are not protected, up to 90 percent tend to also become infected. The contagious virus can linger in a room for two hours.

Two outbreaks in 2019 in undervaccinated communities in New York and New York City caused a large spike in cases, threatening measles’ elimination status in the U.S. In 2020, 12 of the 13 total cases were reported before Covid-19 lockdowns started in March.

The 97 cases in the first quarter of 2024 represent a 17-fold increase over the average number of cases in the first quarters of 2020 to 2023, per the new report.

For all cases since 2020, the median patient age was 3 years old. Unvaccinated people accounted for 68 percent of all cases, and 23 percent of infected people had unknown vaccination statuses. Of 155 people hospitalized with measles, 70 percent were children younger than 5 years old, and 92 percent were either unvaccinated or their status was unknown. No deaths were reported.

Almost all cases were tied to an importation after travel outside the country, and the majority of these cases were among U.S. residents who were unvaccinated or whose vaccination status was unknown. Increased rates of measles globally and decreased vaccination rates both increase the risk for importations, and the CDC recommends children get vaccinated before international travel.

“Public health jurisdictions are reaching out to communities and populations with low vaccination rates, and we feel this approach will be effective,” Marcus Plescia, chief medical officer of the Association of State and Territorial Health Officials, tells CNN’s Deidre McPhillips. “However, the increase in misinformation about measles vaccination undermines these efforts and could ultimately endanger our elimination status.”

Officials want at least 95 percent of the population to be vaccinated, but coverage has remained below this threshold for three consecutive years. Vaccination coverage in kindergartners fell from 95.2 percent in the 2019-2020 school year to 93.1 percent in the 2022-2023 school year. Vaccine coverage estimates are below 90 percent in 12 states and Washington, D.C., per the new report.

The CDC recommends that all children get their first dose of the measles, mumps and rubella vaccine between the ages of 12 months and 15 months and their second and final dose between 4 and 6 years of age.

Will Sullivan | | READ MORE

Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.