Most of the pediatric cases of mumps reported in 2015-’19 occurred in vaccinated children, according to a study published today. Furthermore, more than two-thirds of those hospitalized were up to date on measles, mumps and rubella (MMR) vaccine.
Mumps vaccine was licensed for use in the U.S. in 1967. One dose was recommended in 1977, and two doses of MMR vaccine were recommended in 1989 (the first dose at 12-15 months of age and the second at 4-6 years of age).
Mumps cases dropped from 152,209 in 1968 to 231 in 2003. However, numbers started to rise in the mid-2000s. The number of cases was particularly high in 2006 (6,584), 2016 (6,366) and 2017 (6,109) due to large outbreaks, according to the Centers for Disease Control and Prevention.
The authors of this study noted that 53% of pediatricians surveyed in 2020 said they would never or rarely test for mumps in a fully vaccinated child with parotitis. Therefore, they sought to increase awareness of the current epidemiology of mumps in children to help clinicians caring for patients with parotitis or other mumps complications.
To do so, they looked at the incidence of mumps cases reported by U.S. health departments to the National Notifiable Diseases Surveillance System from 2007 through 2019. They reported their findings on vaccination status, association with an outbreak and other characteristics in “Mumps in vaccinated children and adolescents: 2007–2019” (Shepersky L, et al. Pediatrics. https://doi.org/10.1542/peds.2021-051873).
During the study period, 32% of all mumps cases occurred in children younger than 18. The median annual incidence was highest among 1- to 4-year-olds and 5- to 10-year-olds (5.8 per 1 million children for both groups).
The authors also analyzed cases from 2015-’19. A total of 5,461 cases were reported in children under 18 (27% of all cases). Most states reported cases each year.
Among those whose vaccination status was known, 74% of 1- to 4-year-olds had received one dose of MMR vaccine, and 86% of 5- to 17-year-olds had received two doses.
Nearly all patients experienced parotitis (97%), while 1% had complications, including orchitis, deafness, meningitis and encephalitis.
Three percent were hospitalized, including 69% who were fully vaccinated based on their age.
Two percent of cases were associated with international travel, which the authors said suggests mumps is endemic in the U.S.
“ … the occurrence of pediatric mumps cases among vaccinated patients in most states highlights the need for clinicians to suspect mumps in pediatric patients with parotitis or mumps complications, regardless of age, vaccination status, or travel history,” the authors wrote.
They noted that it may be challenging to diagnose mumps in vaccinated patients because viral loads are lower. Therefore, laboratory tests may not detect mumps RNA.
“Appropriate timing and collection technique of specimens is needed for accurate results,” the authors concluded.
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