Reduced Vaccination Rates May Allow Spike in Measles Cases

Measles outbreaks in the United States quadrupled from 2023 to 2024, while vaccination rates among kindergarteners declined, based on data from the Centers for Disease Control and Prevention (CDC).

The latest information on measles cases and outbreaks showed that 16 measles outbreaks (defined by the CDC as three or more related cases) occurred in 2024 compared with four outbreaks in 2023.

A total of 14 measles cases and two outbreaks have already been reported as of early February, according to the CDC, and nine of these cases were outbreak associated. The 2025 cases occurred in New York City, Alaska, Georgia, Rhode Island, and Texas.

Of the 285 measles cases reported to the CDC in 2024, 42% occurred in children younger than 5 years, 31% in those aged 5-19 years, and 27% in those aged ≥ 20 years.

According to the data from the CDC, measles-mumps-rubella (MMR) vaccination rates for kindergarteners in the United States dropped from 95% in the 2019-2020 school year to approximately 93% in the 2022-2023 school year.

Vaccine coverage rates may vary greatly at the local level, and areas of low vaccination can persist in states with high vaccination coverage overall, according to the CDC. These communities with low or inconsistent vaccination rates may be at increased risk.

Overall, unvaccinated children are at the greatest risk for measles, according to the CDC. The CDC currently recommends two doses of the MMR vaccine for all children, with a first dose at age 12-15 months and a second dose at age 4-6 years.

Other high-risk groups for whom MMR vaccination is advised include young adults at college and other post-high school institutions who lack evidence of immunity, who should receive two doses at least 28 days apart.

Adults without evidence of immunity should receive two doses at least 28 days apart if they are in high-risk settings, such as healthcare or international travel; other adults without evidence of immunity should receive at least one dose of MMR, according to the CDC.

However, certain groups including pregnant women, individuals with immunocompromising conditions, and those with severe allergies to any of the vaccine components should not receive an MMR vaccine, according to the CDC.

An Expert’s Perspective

“Measles cases and outbreaks are increasing due to decreasing vaccination rates,” said Lori Handy, MD, MSCE, associate director of the Vaccine Education Center at the Children’s Hospital of Philadelphia and assistant professor of clinical pediatrics at the Perelman School of Medicine, both in Philadelphia, in an interview.

“In the past, an unvaccinated individual could travel internationally, acquire measles, and bring it back to the United States, but if they returned to a community with high vaccination rates (> 95%), the disease wouldn’t spread,” said Handy. Currently, imported measles cases are occurring in communities with lower vaccination rates, and the highly contagious nature of the virus can cause an outbreak, she said.

For example, “if a person with measles is in a crowd of 10 susceptible people, meaning unvaccinated, or no immunity because of immune suppression, likely all 10 will become infected,” Handy said. Vaccination rates declined overall during the COVID-19 pandemic as a result of increased vaccine hesitancy and limited access to vaccination, she added. “Now, we have highly accessible vaccines again, but there is a growing number of individuals questioning the need for and safety of the vaccine based on misinformation and disinformation spreading through traditional and social media,” she said.

The measles vaccine is highly effective; data show that two doses provide 97% protection, Handy told Medscape Medical News. “Risks associated with the vaccine are not zero, but are incredibly rare,” she said. “It is critical for parents to recognize that when they chose not to vaccinate their child, they are choosing the risk of disease, which is a real threat right now, and measles is terrifying,” she said. Children infected with measles can experience fevers up to 104 °F, and many develop viral pneumonia, which is the most common cause of measles-related death, she said. In addition, “patients can suffer from encephalitis and severe diarrhea or dehydration. One of every 1000 children with measles will die; this is a virus to fear,” Handy emphasized.

Vaccination rates in kindergarteners are an established way to follow trends over time, said Handy. “What these rates indicate, however, is that there is a portion of the population younger than age 5 years that is unvaccinated, despite vaccine being recommended at age 1,” she said. “Unvaccinated young children are generally the population that measles infects, so any delay in routine vaccines for children, specifically the measles vaccine, is a major contributor to outbreaks,” she added.

Handy expressed concern about the continued spread of measles through communities of unvaccinated children. CDC’s measles data are updated monthly, but the most recent data from state and local health departments show more than 60 cases for 2025 as of mid-February, and this is likely an underestimation as there may be undetected cases in some areas of outbreaks, she said. “As long as we have less than 95% of the population vaccinated for measles, we will see outbreaks,” said Handy. Unvaccinated individuals are often found in like-minded communities, so some communities may have vaccination rates as low as 50%, she noted.

Helping Those at Highest Risk

“Populations that lack immunity and have any contact with a person with measles are at extremely high risk of infection,” Handy told Medscape Medical News. These groups may include those younger than 1 year, those who cannot be vaccinated because of an immunodeficiency, those who chose not to be vaccinated, and those who may have been vaccinated but are experiencing immune suppression, such as chemotherapy for cancer, she said.

The best way for high-risk individuals to keep safe is to advocate for measles vaccination in the community, Handy told Medscape Medical News. For those who cannot receive a measles vaccine “surround yourself with people who cannot infect you,” she said.

In many areas, local health alerts will identify locations where a case of measles occurred, Handy noted. If an individual who cannot receive a measles vaccine presents with a report of possible exposure to measles, then they should receive postexposure prophylaxis to reduce the risk for infection, she said.

Managing Cases and Avoiding Outbreaks

Clinicians should continue to advise parents and patients on the signs and symptoms of measles, Handy told MedscapeMedical News. The key symptoms are a high fever, cough, congestion, and red eyes, followed by a red rash that goes from the hairline down the body, she said. Remind patients that if they suspect exposure, contact a healthcare provider before presenting to a medical facility so the patient can enter without exposing other patients to infection, she added. “If a case occurs, work with local public health departments; they can advise on how to counsel exposures, how to treat and isolate a patient, and how to get care for unvaccinated people in the community,” Handy said.

Handy had no relevant financial relationships to disclose.