Mumps Cases and Outbreaks

Key points

  • U.S. mumps cases decreased significantly after the mumps vaccine program began in 1967, but they have increased since 2006.
  • Most recent outbreaks have occurred in settings with intense or frequent close contact, such as college campuses or close-knit communities.
  • These outbreaks and their circulation across the country highlight the importance of high vaccination coverage to limit mumps outbreaks.

Mumps outbreaks still happen

After the U.S. mumps vaccination program started in 1967, there has been a more than 99% decrease in mumps cases in the United States. However, mumps outbreaks still occur, particularly in settings where people have close, prolonged contact, such as universities, schools, and correctional facilities.

During these outbreaks, people who previously had 1 or 2 doses of MMR vaccine can still get mumps. Experts aren't sure why vaccinated people still get mumps, but some evidence suggests that:

  • Some people's immune systems may not respond as well as they should to the vaccine.
  • The mumps vaccine may produce antibodies (proteins created by the body's immune system to help fight infections) that are not as effective against wild-type virus strains.
  • In some people, antibodies from mumps vaccination may decrease overtime, until they no longer protect the person from mumps.
  • As most people are not routinely exposed to mumps, there is less immunologic boosting (where people are exposed to mumps which boosts their immunity, but they do not get sick).

Disease symptoms are milder and complications are less frequent in vaccinated people. High vaccination coverage also helps to limit the size, duration, and spread of mumps outbreaks. So, it's still very important to be up to date on MMR vaccine.

During a mumps outbreak, public health authorities might recommend an additional dose of MMR vaccine for people who belong to groups at increased risk for getting mumps. These groups are usually those who are likely to have close contact, such as sharing sport equipment or drinks, kissing, or living in close quarters, with a person who has mumps.

Your local public health authorities or institution will notify you if you are at increased risk and should receive this additional dose. If you already have 2 doses of MMR, it is not necessary to seek out vaccination unless the authorities tell you that you are part of this group.

Reported U.S. mumps cases by jurisdiction, 2024*

As of July 5, 2024, 37 jurisdictions reported a total of 214 mumps cases.*

Reported U.S. mumps cases by year (2000–2024)

*Jurisdictions refer to any of the 50 states, New York City, and the District of Columbia.

**2024 map represents cases reported to CDC as of July 5, 2024; 2021–2024 case counts are preliminary and subject to change.

Mumps cases

Before mumps vaccine was available in the United States, most children got mumps by the time they reached adolescence.

Reported cases decreased by more than 99% after both the mumps vaccination program started in the United States in 1967 children regularly received two doses of MMR vaccine. Cases decreased from 152,209 in 1968 to 231 in 2003.

However, reported U.S. mumps cases and outbreaks increased since 2006. Most of these cases were in young adults and vaccinated people.

Large outbreaks happened in settings where people have intense or frequent close contact, like college campuses, close-knit communities, and large gatherings.

Previous Years

Mumps cases decreased compared with the previous six years, possibly due to social distancing and other COVID-19 prevention measures. However, mumps continued to circulate across the U.S. despite these measures. From April 1, 2020 to December 31, 2020, 32 health departments reported 142 mumps cases.

The U.S. saw a range of different mumps outbreak settings and sizes. Cases started to increase in late 2015.

From January 2016 to June 2017, health departments reported 150 outbreaks (9,200 cases). Outbreaks occurred in households, schools, universities, athletics teams and facilities, church groups, workplaces, and as a result of large parties and events.

The largest outbreak occurred in a close-knit community in northwest Arkansas that resulted in nearly 3,000 cases.

Two large outbreaks in Iowa and Illinois each involved several hundred university students.

About half of the outbreaks involved more than 10 cases.

From September 1, 2018, to August 22, 209, 19 state health departments reported 898 mumps cases in adult migrants detained in 57 detention facilities.

One outbreak involved over 3,000 people and mostly affected students who were part of a close-knit religious community in New York City and attended schools where they participated in close-contact activities. The outbreak started when an infected student returned from the United Kingdom where a large mumps outbreak was occurring.

The second outbreak involved about 500 people, mostly school-aged children, in the U.S. Territory of Guam.

The United States experienced a multi-state mumps outbreak involving more than 6,500 reported cases. This resurgence mostly affected Midwest college-aged students on many different Midwestern college campuses