Mumps in Vaccinated Children and Adolescents

Abstract

Source: Shepersky L, Marin M, Zhang J, et al. Mumps in vaccinated children and adolescents: 2007–2019. Pediatrics. 2021;148(6): e2021051873; doi.10.1542/peds.2021-051873Investigators from the CDC, Atlanta, GA, conducted a retrospective study to describe the incidence of mumps in children in the US and assess demographic and vaccination characteristics of those with mumps. For the study, they reviewed data in the National Notifiable Diseases Surveillance System (NNDSS) and identified cases of mumps in youths <18 years old in the US between 2007 and 2019. Data from the entire study period were analyzed to characterize pediatric mumps cases by age, state of residence, mumps vaccination status, and whether cases were outbreak-associated. Annual age-specific incidence rates were calculated. A focused analysis was conducted on pediatric mumps cases during the period 2015–2019. In addition to demographic information, data on import status (defined as a case in a child following international travel), parotitis, and complications (orchitis, deafness, meningitis, and encephalitis) were collected. Patients 1-4 years old were classified as up-to-date (UTD) for mumps vaccination if they had received 1 dose of mumps vaccine, and those 5-17 years old were classified as UTD if they had received 2 doses.Between 2007 and 2019, 28,306 mumps cases were reported to NNDSS, including 9,172 (32%) in children. Mumps was reported in all 50 states and the District of Columbia. The annual median number of pediatric mumps cases was 349, with peaks in 2009– 2010 (2,627 pediatric cases) and 2016–2017 (4,093 pediatric cases). Overall, the median annual incidence of mumps in children was 4.7 cases/1,000,000 population. Median annual incidence was 5.8 cases/1,000,000 population in children 5-10 years old and 5.8 cases/1,000,000 population in those 1-4 years of age. During the study period, 64% of pediatric mumps cases with available data were outbreak-associated. Among children with mumps, 89% had ≥1 dose of mumps vaccine.Between 2015 and 2019, 5,461 mumps cases were reported in children. During this period, 54% of pediatric mumps cases occurred in youths 11-17 years old, 33% in those 5-10 years old, 13% in children 1-4 years old, and 1% in infants <1 year old. Only 2% of pediatric cases were associated with international travel. During this period, 74% of children 1-4 years old with mumps and 86% of those 5-17 years old were UTD for mumps vaccination. Among 4,471 cases of pediatric mumps, parotitis was present in 97%. Complications occurred in 75 cases (1%), including orchitis in 2% of boys, deafness in 10 children, meningitis in 3, and encephalitis in 2.The authors conclude that since 2007, 32% of mumps cases in the US occurred in children, most of whom had been vaccinated.Dr Brady has disclosed no financial relationship relevant to this commentary. This commentary does not contain a discussion of an unapproved/investigative use of a commercial product/device.Mumps can occur in fully vaccinated individuals. (See AAP Grand Rounds. 2017;37[6]:64.)1 Two explanations have been suggested for the occurrence of mumps in vaccinated persons: waning of vaccine-induced immunity and antigenic mismatch between the vaccine strain and the circulating wild-type mumps strains.2 Rubin et al3 reported that mumps antibodies declined to near baseline levels 10 years after vaccination for children vaccinated with the second dose at age 4 to 6 years. Additionally, these vaccine-induced antibody responses were lower against the circulating wild-type strains (predominantly genotype G in the US) than against the vaccine strain (genotype A).3-4The current authors noted that 97% of children with mumps presented with parotitis. As prior mumps vaccination does not exclude mumps, diagnostic testing is a consideration when children present with parotitis or mumps complications (eg, orchitis). The preferred test is a buccal swab specimen to detect mumps virus nucleic acid by quantitative reverse transcriptase-polymerase chain reaction (RT-qPCR).5 When buccal swab specimens were collected <2 days after symptom onset, the sensitivity of RT-qPCR was about 83%.1 Therefore, failure to detect mumps virus RNA by RT-qPCR in samples from persons with parotitis does not exclude mumps as a diagnosis. Vaccinated persons may shed small amounts of virus for short periods.5 In previously vaccinated persons who acquire mumps, the mumps-specific immunoglobulin (Ig) M response may be transient, delayed, or not detected.5 Thus, a negative IgM also does not exclude mumps as a diagnosis.With the 2-dose measles-mumps-rubella (MMR) vaccine policy, mumps cases in the US decreased by >99%.6 However, mumps still occurs in vaccinated persons. Parotitis is the hallmark of mumps, and RT-qPCR to detect mumps RNA from a buccal swab specimen is the preferred diagnostic test.A third dose of the current MMR vaccine has been administered during mumps outbreaks.4 A third dose of a mumps vaccine using an alternative mumps strain, however, is a consideration to boost and broaden immunity in vaccine recipients.4