Mumps in Vaccinated Children and Adolescents: 2007-2019.

Background: Despite a >99% reduction in US mumps cases after the introduction of mumps vaccine in 1967, outbreaks have occurred in schools and other settings involving vaccinated children and adolescents since 2006.

Methods: We analyzed mumps cases reported by US health departments to the National Notifiable Diseases Surveillance System. We present the incidence and vaccination status of pediatric cases (age <18 years) during 2007-2019 and describe demographic, clinical, and vaccination characteristics of pediatric cases reported during the most recent resurgence in 2015-2019.

Results: During 2007-2019, 9172 pediatric cases were reported, accounting for a median of 32% of all cases reported each year (range: 13%-59%). A median of 87% (range: 81%-94%) of pediatric patients each year had previously received ≥1 measles, mumps, and rubella (MMR) vaccine dose. During 2015-2019, of 5461 pediatric cases reported, only 2% of those with known import status (74%) were associated with international travel. One percent of patients had complications and 2% were hospitalized. Among patients aged ≥1 year with known vaccination status (72%), 74% of 1- to 4-year-olds had received ≥1 MMR dose and 86% of 5- to 17-year-olds had received ≥2 MMR doses. Since 2016, pediatric mumps cases have been reported in most US states each year (range: 38-45 states).

Conclusions: Since 2007, one-third of US reported mumps cases occurred in children and adolescents, the majority of whom were vaccinated. Clinicians should suspect mumps in patients with parotitis or mumps complications, regardless of age, travel history, and vaccination status.