How common are measles deaths in the United States as vaccination rates fall?

By Jen Christensen, CNN

(CNN) — A fourth person with measles has died in Pennsylvania, the state announced Tuesday — marking the first time in decades the United States has recorded so many deaths in a single year.

Measles deaths have been extremely rare in the United States because most people are protected by a highly effective vaccine. But as vaccination rates decline nationally and measles cases rise globally, experts say the death toll from measles may continue to grow in the United States this year and beyond.

How common are measles deaths in the United States?

The last year with at least four measles deaths in the United States was 1992.

Until the recent resurgence in cases, the United States went several years without any measles deaths.

Last year, there were three measles deaths, and before then, the last measles death was in 2015, when a Washington state woman died. Before then, the United States hadn’t had a measles death since 2003.

This year was already the second record-breaking year in a row for measles cases. As of July, the country has recorded more measles cases than in any other year since 1991.

Before the vaccine became available in 1963, measles sickened 3 million to 4 million people and led to about 500 deaths every year in the United States.

Measles was declared eliminated from the United States in 2000, but recent outbreaks mean that status will be reassessed in November.

How common are measles deaths globally?

Measles deaths are much more common in low-income countries with weaker health infrastructure than in the United States or similar countries.

Globally, an estimated 95,000 people died from measles in 2024, according to the World Health Organization. Ninety-five percent of those deaths were in low-income countries.

Measles is considered the most contagious infectious disease known to humans; up to 9 out of 10 unvaccinated people who come in contact with an infected person will catch the virus. Vaccinations have proven highly successful, preventing an estimated 59 million deaths from 2000 to 2024, WHO said.

Before widespread vaccination, measles caused an estimated 2.6 million deaths globally each year.

Is this number of deaths unexpected?

Globally, measles typically kills nearly 3 out of every 1,000 people who get sick; in the United States, it’s about 1 in 1,000, research shows.

As of this week, Pennsylvania had counted at least 693 measles cases, 133 hospitalizations and four deaths, according to the Pennsylvania health department.

The official tally is likely an undercount. Measles cases are often unreported when people have milder symptoms and don’t see a doctor who would report the case.

Pennsylvania’s death toll is “on the high side,” said Johns Hopkins University Professor Dr. William Moss, an epidemiologist who has studied measles for years.

Moss believes the higher number of deaths in Pennsylvania “reflects the fact that these infections occurred in individuals, except for the 18-year-old, with underlying risk factors for severe illness and mortality, particularly the two infants.”

One infant who died had a ruptured spleen and died shortly after birth.

The other infant had Amish microcephaly, a rare and severe genetic disorder that causes a small head and underdeveloped brain and leaves children with little chance of surviving beyond a couple of months, Moss said.

The 40-year-old woman who died had chronic obstructive pulmonary disease, which increased her risk for a severe lung infection from measles.

“They’re all tragic cases, all unvaccinated cases, but kind of unique in their underlying risk factors for severe measles,” Moss said.

What is acute disseminated encephalomyelitis?

The Mifflin County, Pennsylvania, coroner said this week that an 18-year-old with measles died from acute disseminated encephalomyelitis, known as ADEM.

Acute disseminated encephalomyelitis is a severe neurological complication of measles that triggers rapid inflammation and swelling in the brain and spinal cord. It develops in about 1 in 1,000 measles cases.

“It’s just a relatively rare, but known complication of measles that can occur in anyone, even otherwise healthy individuals,” Moss said.

Could there be something new or worse about the virus circulating now?

Neither Moss nor Dr. David Margolius, director of the Cleveland Department of Health, believes the virus has mutated to become more deadly.

There may be more deaths because there are more cases and fewer people are getting vaccinated, Margolius said.

“So it’s been given a door in, and it’s taken advantage and the virus has spread across many populations across the world,” Margolius said.

Are vaccinated people at risk of death from measles?

There is no specific treatment for measles, so prevention is the best way to reduce risk of serious illness or death. The measles vaccine is highly effective, providing 97% protection for most people.

“It’s not perfect and we have a two-dose vaccine schedule for a reason,” Moss said. “Not everyone responds to the first dose.”

The risk of death from measles for vaccinated people is “very low, unless you’re immunosuppressed in some way,” Moss said.

Measles, mumps and rubella protection are combined into one vaccine administered when a baby is between 12 to 15 months old. Children get a second dose between ages 4 and 6. For most people, protection provided by the vaccine lasts a lifetime.

Who’s most at risk of serious illness from measles?

Measles can be serious for anyone at any age, but some groups are more at risk of serious complications, including:

• Children younger than 5
• Adults older than 20
• People who are pregnant
• People with weakened immune systems from conditions such as HIV or leukemia

What are some of the long-term risks of measles infection?

Measles is well known for its rash, fever and cough, but it can also cause seizures, blindness, deafness and permanent lung damage.

Measles can also weaken the central nervous system and immune system, resulting in serious disease or death years later.

The measles virus can also essentially wipe out the body’s previous immune memory, making people vulnerable to other dangerous infections, even long after they recover from the initial infection.

Subacute sclerosing panencephalitis, or SSPE, is a rare but fatal central nervous system disease that can develop seven to 10 years after a person is infected and seems to have recovered.

Before vaccination was widely available, about 1,000 people developed chronic disability from acute encephalitis caused by measles annually, according to the CDC.

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