Atlanta—Despite the overwhelming success of vaccination, cases of mumps are neither gone nor forgotten in children and adolescents, according to a report from CDC authors.

The article in Pediatrics notes that U.S. mumps cases plummeted 99% after the introduction of a vaccine in 1967. However, it also notes that outbreaks have continued to occur in schools and other settings involving vaccinated children and adolescents since 2006.

Researchers analyzed mumps cases reported by U.S. health departments to the National Notifiable Diseases Surveillance System. The article discussed the incidence and vaccination status of pediatric cases during 2007–2019, including demographic, clinical, and vaccination characteristics reported during the most recent resurgence of cases occurring from 2015 to 2019.

"During 2007–2019, 9172 pediatric cases were reported, accounting for a median of 32% of all cases reported each year (range: 13%–59%)," the authors point out. "A median of 87% (range: 81%–94%) of pediatric patients each year had previously received >1 measles, mumps, and rubella (MMR) vaccine dose."

The study advises that during 2015Ð2019, of the 5,461 pediatric cases reported, only 2% of those with known import status (74%) were associated with international travel. Complications occurred in 1% of the cases, and 2% were hospitalized.

The authors also describe how, among the 72% of patients aged 1 year or older with known vaccination status, 74% of 1- to 4-year-olds had received one or more MMR dose and 86% of 5- to 17-year-olds had received two or more MMR doses. Yet, since 2016, pediatric mumps cases have been reported in most U.S. states each year.
"Since 2007, one-third of U.S. reported mumps cases occurred in children and adolescents, the majority of whom were vaccinated," researchers emphasize. "Clinicians should suspect mumps in patients with parotitis or mumps complications, regardless of age, travel history, and vaccination status."

According to the CDC, mumps typically presents as a mild illness of puffy cheeks and swollen jaw from parotitis; it cautions, however, that complications such as orchitis, oophoritis, pancreatitis, hearing loss, meningitis, and encephalitis can occur.

Before widespread vaccination, mumps was a universal childhood disease and one of the most common causes of aseptic meningitis and encephalitis, according to the report.

While the Advisory Committee on Immunization Practices initially recommended one dose of mumps vaccine for routine use in 1977, 11 years later it recommended that all children receive two doses of the MMR vaccine for measles control, with the first dose at age 12 to 15 months and the second dose at age 4 to 6 years.

As a result of those policy changes, reported mumps cases in the U.S. fell from 152,209 in 1968 to 231 in 2003.

Mumps cases began to rise, however, starting in the mid-2000s. The article described several peak years in that period:

• The first peaks in 2006 (6,584 cases reported) and 2009–2010 (4,603 cases reported) were mainly driven by a few large, localized outbreaks.

• In the next peak during 2016–2017, numerous mumps outbreaks were reported across the U.S. in various settings, with more than 150 outbreaks reported in 37 states and the District of Columbia, totaling more than 9,000 outbreak-associated cases.

• In 2018–2019, mumps cases dropped slightly compared with other nonpeak years but remained elevated at 6,294 cases.

"The majority of cases since 2006 have occurred among college-aged young adults, most of whom have received 2 doses of MMR vaccine, leading many experts to hypothesize that waning immunity by young adulthood is the cause for the outbreaks," the authors explain. "However, outbreaks also occurred among children and adolescents, including large outbreaks in an Orthodox Jewish community in New York, the U.S. Territory of Guam, and a Marshallese community in Arkansas. In these outbreaks, among school-aged children with known vaccination status, 85% to 93% had previously received the recommended 2 MMR doses. Despite these data, a 2020 survey of US pediatricians revealed 53% would rarely or never test for mumps in a fully vaccinated child with parotitis."

The goal, according to the authors, is to increase awareness among pharmacists and other healthcare professionals of the possibility of mumps in patients with parotitis and the risk of complications.

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