Measles cases surge worldwide, infecting 10.3 million people in 2023: WHO

Last year, there were 10.3 million cases of measles globally -- an increase of 20% from the previous year, according to a newly released report from the World Health Organization.

Nearly 107,500 people died from measles worldwide in 2023 and children under the age of 5 were hit the hardest, the report found.

Measles is a highly infectious virus often characterized by a distinctive red, spotty rash that starts on the face and spreads downward, often merging into larger patches.

Both children and adults may develop potentially deadly complications, including pneumonia, which is a serious lung infection, or encephalitis, which is swelling in the brain. It can also lead to deafness, long-term intellectual disability, and complications during pregnancy.

In the United States, there have been 277 measles cases reported across 30 states and the District of Columbia in 2024, more than four times the number of cases last year when there were 59 cases, according to data from the Centers for Disease Control and Prevention. Additionally, there were 16 outbreaks in 2024 compared to just four in 2023.

A measles outbreak is defined as three or more related cases, with disruptive outbreaks defined as 20 or more cases per 1 million people in a year.

"The alarming rise in measles cases globally and here in the U.S. is a stark reminder of the consequences of falling vaccination rates," said Dr. John Brownstein, chief innovation officer at Boston Children's Hospital and an ABC News medical contributor. "We're seeing preventable outbreaks that endanger the most vulnerable among us -- especially young children."

Measles vaccination rates have been under the national target of 95% for at least three years, according to the CDC. Brownstein added that the surge in cases was worsened by the COVID-19 pandemic, which led to millions of children missing routine childhood vaccinations. An estimated 96% of measles cases this year were in children who were not fully vaccinated.

"We're now seeing the ripple effects of those missed doses, emphasizing the critical need to strengthen vaccination campaigns and public health initiatives to regain lost ground," Brownstein said.

The CDC recommends two doses of the measles vaccine for children, starting with the first dose anytime between the ages of 12 and 15 months followed by a second dose anytime between ages four and six years. Both the WHO and CDC recommend better surveillance to catch measles cases early.

The number of children receiving the first dose of measles vaccine worldwide declined to 81% during the COVID-19 pandemic, the lowest rate since 2008, WHO data showed. This left millions of children unprotected from the virus and resulting in more cases and outbreaks despite more countries offering the vaccine since 2000.

The agency recommended a 95% vaccine coverage target rate for countries to achieve or maintain measles elimination status.

Esther Zusstone, MD, is a radiology resident at NYU Langone, and a member of the ABC News Medical Unit.