Health officials across the United States are reporting small but notable increases in mumps cases, a contagious viral infection that once infected hundreds of thousands of Americans each year before vaccination dramatically reduced its spread.
According to the U.S. Centers for Disease Control and Prevention, 11 jurisdictions have reported 34 cases so far this year, a reminder that the disease still circulates despite decades of vaccination.
Mumps was once a routine childhood illness in the United States. Before the vaccine was introduced, outbreaks were common and infections numbered in the hundreds of thousands annually. But after the first mumps vaccine was approved in 1967 and later incorporated into the measles, mumps and rubella (MMR) vaccine, cases declined dramatically.
By 2003, only 231 cases were reported nationwide, a drop of more than 99%.
Still, outbreaks have occurred periodically since 2006, particularly in places where people live, work or study in close quarters.
What mumps is and how it spreads
Mumps is a viral infection that primarily affects the salivary glands, especially the parotid glands located just below and in front of the ears. The infection spreads through respiratory droplets or direct contact with saliva, meaning the virus can be transmitted when an infected person coughs, sneezes, talks or shares drinks or utensils.
The disease can also spread during close-contact activities such as sports, dancing or kissing.
One reason mumps can spread easily is that people can be contagious before they realize they are sick. A person infected with mumps can transmit the virus several days before swelling begins and for up to five days after symptoms appear.
Because of this, public health officials advise people diagnosed with mumps to stay home from work or school and avoid social gatherings during that period.
Settings where people are in frequent close contact — such as schools, college campuses, sports teams and households — are especially vulnerable to outbreaks.
Symptoms often appear weeks after exposure
People infected with mumps typically do not develop symptoms right away. The incubation period usually lasts two to four weeks after exposure.
The most recognizable symptom is painful swelling of one or both salivary glands, which causes the characteristic puffy cheeks and tenderness along the jawline.
Other symptoms often appear before or alongside the swelling and may include:
- Fever
- Headache
- Muscle aches
- Fatigue
- Loss of appetite
- Pain when chewing or swallowing
In many children, the illness is relatively mild. Some may experience only minor swelling or a low-grade fever, while others may show few symptoms at all.
Adolescents and adults, however, are more likely to develop more severe illness and complications.
Possible complications
Most people recover from mumps within about two weeks, but the virus can occasionally lead to serious complications.
One of the most well-known is orchitis, an inflammation of the testicles that can occur in males after puberty. Although painful, it rarely leads to infertility.
Females may develop oophoritis, inflammation of the ovaries, or mastitis, inflammation of breast tissue.
The virus can also affect the central nervous system. Meningitis, an inflammation of the lining surrounding the brain and spinal cord, occurs in a small percentage of cases. Encephalitis, or inflammation of the brain itself, is rare but potentially life-threatening.
Another uncommon but serious complication is permanent hearing loss.
People who are not vaccinated face the highest risk of infection and complications.
Vaccination remains the best protection
Health experts emphasize that vaccination remains the most effective way to prevent mumps.
The MMR vaccine protects against measles, mumps and rubella. Children typically receive the first dose between 12 and 15 months of age and a second dose between 4 and 6 years old.
Two doses of the vaccine are about 86% effective at preventing mumps infection, while one dose is about 72% effective, according to the CDC.
No vaccine provides perfect protection, and some vaccinated individuals can still become infected. These cases are known as breakthrough infections. When they occur, symptoms are usually milder and complications are less common.
Scientists also believe that immunity against mumps may decline somewhat over time, which can contribute to outbreaks among young adults who were vaccinated in early childhood.
This is why clusters of cases sometimes occur on college campuses or in other close-knit communities, even when vaccination rates are high.
Who should be especially cautious
Anyone who has not been vaccinated against mumps is at risk of infection.
Some groups face higher exposure risks because of frequent close contact with others. These include school-age children, college students, healthcare workers and people living in communal settings.
International travelers may also face greater risk when visiting countries where mumps remains common.
Public health officials may sometimes recommend an additional dose of the MMR vaccine during outbreaks for people considered at higher risk of exposure. The additional dose can temporarily boost immunity and help slow transmission.
A reminder that prevention still matters
Even relatively small increases in mumps cases serve as a reminder that vaccine-preventable diseases have not disappeared.
Health experts say maintaining high vaccination rates, recognizing symptoms early and limiting contact during illness remain key steps in preventing the virus from spreading within communities.
While most people recover fully, the disease’s potential complications make prevention — and vaccination — an important public health priority.