Mumps Cases on the Rise as Vaccination Rates Dip

Public health experts warn of increasing mumps cases, especially in communities with lower vaccination rates.

Mar. 16, 2026 at 10:10pm

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While measles outbreaks have been grabbing headlines, public health officials are also keeping a close eye on the resurgence of another vaccine-preventable illness - mumps. After a dramatic decline following the introduction of the MMR vaccine in 1967, mumps cases are on the rise again in the U.S., with 34 confirmed or probable cases reported by the CDC by the end of February 2026. Experts attribute this to waning immunity, lower vaccination rates in some communities, and the relatively lower effectiveness of the mumps vaccine compared to the measles vaccine.

Why it matters

Mumps can lead to serious complications like meningitis and orchitis, and outbreaks can spread quickly in close-contact settings like schools and colleges. The rise in cases highlights the importance of maintaining high vaccination rates to achieve herd immunity and prevent the spread of vaccine-preventable diseases.

The details

While measles is more contagious, the mumps vaccine is less effective, with one dose being about 72% effective and two doses around 86% effective. This means some vaccinated people can still develop mumps after exposure, a phenomenon known as 'breakthrough infection'. Waning immunity over time is also contributing to the increase in cases, particularly in older adolescents and adults.

  • By the end of February 2026, the Centers for Disease Control and Prevention had identified 34 mumps cases this year.
  • Before the launch of the MMR vaccination program in 1967, most children in the United States got mumps by adolescence.
  • After the program began, reported cases dropped by more than 99 percent — from roughly 150,000 in 1968 to about 230 in 2003.

The players

Christy Beneri, DO

The assistant medical director of infection prevention and control at Stony Brook Children's Hospital in Stony Brook, New York.

Yvonne Maldonado, MD

A professor of pediatrics and infectious diseases at Stanford University in California.

Amesh Adalja, MD

A senior scholar at the Johns Hopkins Center for Health Security in Baltimore.

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What they’re saying

“One dose of the vaccine is about 72 percent effective, and two doses are about 86 percent effective.”

— Christy Beneri, DO, Assistant medical director of infection prevention and control at Stony Brook Children's Hospital

“Current mumps cases in the U.S. may be the result of a combination of undervaccination in some communities as well as the lower effectiveness of the vaccine.”

— Yvonne Maldonado, MD, Professor of pediatrics and infectious diseases at Stanford University

“The most common complication is orchitis, or inflammation of the testicles, which can lead to testicular atrophy and potentially affect fertility.”

— Amesh Adalja, MD, Senior scholar at the Johns Hopkins Center for Health Security

What’s next

Public health authorities may recommend an extra dose of the MMR vaccine for people at increased risk of exposure during mumps outbreaks.

The takeaway

The rise in mumps cases highlights the importance of maintaining high vaccination rates to achieve herd immunity and prevent the spread of vaccine-preventable diseases. Vaccination remains the most effective way to protect against mumps and its potentially serious complications.