Video Abstract

Video Abstract

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.

What’s Known on This Subject:

After the introduction of mumps vaccine in 1967, US mumps cases declined by >99%; however, since 2006 there has been an increase in mumps cases, with outbreaks reported in schools and other settings involving vaccinated children and adolescents.

What This Study Adds:

During 2007–2019, approximately one-third of US mumps cases reported each year were among patients aged <18 years, the majority of whom were vaccinated. Clinicians should suspect mumps in pediatric patients with parotitis or mumps complications, regardless of vaccination status.

Mumps typically presents as a mild illness of puffy cheeks and swollen jaw from parotitis; however, complications such as orchitis, oophoritis, pancreatitis, hearing loss, meningitis, and encephalitis can occur.1  Before the licensure of mumps vaccine in the United States in 1967, mumps was a universal childhood disease and one of the most common causes of aseptic meningitis and encephalitis.

The Advisory Committee on Immunization Practices initially recommended 1 dose of mumps vaccine for routine use in 1977.2,3  In 1989, Advisory Committee on Immunization Practices recommended that all children receive 2 doses of measles, mumps, and rubella (MMR) vaccine for measles control, with the first dose at 12 to 15 months of age, and the second dose at 4 to 6 years of age.4  After vaccine introduction and implementation of the 2-dose MMR vaccination policy, reported mumps cases in the United States fell from 152 209 in 1968 to 231 in 2003, a >99% reduction.3,5 

Starting in the mid-2000s, however, mumps cases began to increase in the United States, with several peak years. The first peaks in 2006 (6584 cases reported) and 2009–2010 (4603 cases reported) were mainly driven by a few large, localized outbreaks.68  In the next peak during 2016–2017, numerous mumps outbreaks were reported across the United States in various settings, with >150 outbreaks reported in 37 states and the District of Columbia (>9000 outbreak-associated cases).9  During 2018–2019, mumps cases decreased but were still elevated compared with other nonpeak years (6294 cases). The majority of cases since 2006 have occurred among college-aged young adults, most of whom have received 2 doses of MMR vaccine,6,10  leading many experts to hypothesize that waning immunity by young adulthood is the cause for the outbreaks. However, outbreaks also occurred among children and adolescents, including large outbreaks in an Orthodox Jewish community in New York, the US Territory of Guam, and a Marshallese community in Arkansas.7,8,11  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.12 

In this article, we report on incidence, vaccination status, and outbreak association of pediatric mumps cases reported in the United States during 2007–2019 and further describe the characteristics of pediatric cases that occurred during the most recent increase in mumps cases during 2015–2019. This update is meant to increase awareness among clinicians of the current epidemiology of pediatric mumps to help them make informed clinical decisions for patients with parotitis or other mumps complications.

Mumps is a nationally notifiable disease: US health department jurisdictions report all confirmed and probable mumps cases to the Centers for Disease Control and Prevention through the National Notifiable Diseases Surveillance System (NNDSS). Cases are classified by health departments according to the Council of State and Territorial Epidemiologists (CSTE) mumps case definitions; mumps CSTE case definitions were updated in 2008, 2010, and 2012 (Supplemental Table 3).1315  We defined pediatric mumps cases as those that occurred among children and adolescents aged <18 years. We included in the analysis cases reported by the 50 US state and the District of Columbia health departments.

To assess characteristics over time, we analyzed confirmed and probable mumps cases reported to NNDSS from January 1, 2007, through December 31, 2019. Variables analyzed included age, state of residence, vaccination status, and whether the case was outbreak-associated. Annual age-specific incidence rates (per 1 000 000 population) were calculated by using the National Center for Health Statistics’ vintage bridge-race postcensal population estimates.16,17  Because annual incidence and other case characteristics varied widely each year, we report the median (eg, median annual incidence) and range across years to provide an overall estimate during the study period.

To describe current epidemiology and characteristics of pediatric mumps cases during the most recent resurgence, we analyzed cases reported to NNDSS from January 1, 2015, through December 31, 2019. Variables analyzed included sex, age, race and ethnicity, state of residence, import status, outbreak-associated, vaccination status, parotitis, complications, hospitalization, and death. Complications captured in NNDSS include orchitis, deafness, meningitis, and encephalitis. Data on other mumps complications, such as pancreatitis, oophoritis, and mastitis, were not available. We defined geographic regions according to US Census classifications.18  Patients were considered vaccinated if they had at least 1 dose of MMR. “Up to date” vaccination status was assigned on the basis of the recommended number of MMR doses for the respective age group: patients 1 to 4 years old were up to date if they had 1 dose of MMR and patients 5 to 17 years old were up to date if they had 2 doses of MMR.

Results for the same analyses on adult cases are provided for comparison in the Supplemental Information. Analyses were performed by using SAS version 9.4 (SAS Institute, Inc, Cary, NC).

During 2007–2019, US health departments reported 28 306 mumps cases, of which 9172 (32%) were pediatric cases (median age = 11 years; range: 0–17). All 50 states and the District of Columbia reported mumps cases during this period, with a median of 212 cases (range: 4–5040) per state, and a median of 48 pediatric cases (range: 3–2263) per state.

Overall, the median number of mumps cases per year was 1328 (range: 229–6369), of which the median number of pediatric mumps cases reported each year was 349 (range: 92–2329) representing a median of 32% of mumps cases each year (range: 13%–59%). There were 2 peaks in pediatric cases in 2009–2010 (2627 cases) and 2016–2017 (4093 cases), coinciding with peaks in all cases (Supplemental Fig 6).

Overall mumps median annual incidence was 4.1 per 1 000 000 population (range: 0.7–19.7). Median annual pediatric incidence was 4.7 per 1 000 000 population (range: 1.3–31.6) (Fig 1). The pediatric age groups with the highest median annual incidence were 5- to 10-year-olds (5.8 per 1 000 000; range: 1.5–34.4) followed by 1- to 4-year-olds (5.8 per 1 000 000; range: 1.9–16.2); however, incidence for each age group varied widely by year (Fig 2). In peak years, among pediatric cases, mumps incidence increased with increasing age of the age group (ie, incidence was higher in older age groups). In nonpeak years, incidence was generally similar across all age groups. Pediatric mumps incidence was lowest in <1-year-olds for all years except 2012. Of all age groups, including adult age groups, median annual incidence was highest among 18- to 22-year-olds (16.1 per 1 000 000; range: 0.7–88.7) (Supplemental Fig 7).

FIGURE 1

Incidence of pediatric and all reported mumps cases: United States, 2007–2019 (N = 28 306).

FIGURE 1

Incidence of pediatric and all reported mumps cases: United States, 2007–2019 (N = 28 306).

FIGURE 2

Incidence of reported pediatric mumps patients by age group: United States, 2007–2019.

FIGURE 2

Incidence of reported pediatric mumps patients by age group: United States, 2007–2019.

Among all pediatric patients during the study period who had information on whether they were vaccinated (79% of patients), 89% had ≥1 MMR dose (median = 87% of patients, range: 81%94% per year) (Fig 3).

FIGURE 3

Pediatric mumps patients by vaccination status: United States, 2007–2019 (N = 7238); 1934 (21%) pediatric patients did not have information on vaccination status.

FIGURE 3

Pediatric mumps patients by vaccination status: United States, 2007–2019 (N = 7238); 1934 (21%) pediatric patients did not have information on vaccination status.

Among cases with information available on whether they were associated with an outbreak (78% of cases), 64% were outbreak-associated. In most years, the largest proportion of pediatric cases were not outbreak-associated (ie, sporadic cases) (median outbreak-associated: 39%, range: 2%–93% per year), except for 2016 and 2017, when 93% and 85% of cases were outbreak-associated, respectively (Fig 4).

FIGURE 4

Pediatric mumps cases by reported association with an outbreak: United States, 2007–2019 (N = 7169); 2003 (22%) pediatric patients (aged <18 years) did not have information on outbreak association.

FIGURE 4

Pediatric mumps cases by reported association with an outbreak: United States, 2007–2019 (N = 7169); 2003 (22%) pediatric patients (aged <18 years) did not have information on outbreak association.

During 2015–2019, 5461 mumps cases were reported among children and adolescents, representing 27% of all reported US cases. Since 2016, pediatric mumps cases have been reported in most US states each year (range: 38–45 states).

Among pediatric cases, 55% occurred among males (Table 1). By age group, cases occurred most frequently among children and adolescents aged 11 to 17 years (54%), followed by children aged 5 to 10 years (33%), 1 to 4 years (13%), and <1 year (1%). Non-Hispanic Asian and/or Pacific Islander was the most frequently reported ethnicity and race (38%), followed by non-Hispanic White (22%). More than half of all pediatric cases during 2015–2019 were in the South US Region. Among those with information on import status (74%), only 2% of all pediatric mumps cases were associated with international travel and assessed to likely have acquired mumps while outside the United States (ie, import cases). Sex, ethnicity and race, region, and import status proportions were similar across age groups. Among those with information on outbreak association (92%), cases in patients aged 5 to 10 years (78%) and 11 to 17 years (86%) were more frequently outbreak-associated than those in children aged 1 to 4 years (39%) and <1 year (45%) (Table 1).

TABLE 1

Demographic Characteristics, Hospitalization, and Complications of Pediatric Mumps Patients by Age Group: United States, 2015–2019 (N = 5461)

No. (%) Mumps Patients by Age Group, y
<1 (n = 61)1–4 (n = 692)5–10 (n = 1786)11–17 (n = 2922)Total (N = 5461)
Year      
 2015 30 (4) 44 (2) 97 (3) 171 (3) 
 2016 17 (28) 196 (28) 846 (47) 1270 (43) 2329 (43) 
 2017 14 (23) 185 (27) 518 (29) 1047 (36) 1764 (32) 
 2018 14 (23) 142 (21) 204 (11) 245 (8) 605 (11) 
 2019 16 (26) 139 (20) 174 (10) 263 (9) 592 (11) 
Sex      
 Male 35 (57) 409 (59) 946 (53) 1634 (56) 3024 (55) 
 Female 26 (43) 280 (40) 835 (47) 1280 (44) 2421 (44) 
 Unknown 3 (<1) 5 (<1) 8 (<1) 16 (<1) 
Race and ethnicity      
 Asian/Pacific Islander, non-Hispanica 19 (31) 152 (22) 703 (39) 1187 (41) 2061 (38) 
 White, non-Hispanic 15 (25) 167 (24) 397 (22) 618 (21) 1197 (22) 
 Hispanic 11 (18) 140 (20) 289 (16) 436 (15) 876 (16) 
 African American, non-Hispanic 3 (5) 39 (6) 63 (4) 162 (6) 267 (5) 
 Other, non-Hispanic 1 (2) 10 (1) 31 (2) 57 (2) 99 (2) 
 American Indian/Alaskan Native, non-Hispanic 8 (<1) 16 (<1) 24 (<1) 
 Unknown 12 (20) 184 (27) 295 (17) 446 (15) 937 (17) 
Regionb      
 South 28 (46) 259 (37) 1004 (56) 1526 (52) 2817 (52) 
 West 12 (20) 131 (19) 385 (22) 803 (27) 1331 (24) 
 Midwest 7 (11) 122 (18) 189 (11) 354 (12) 672 (12) 
 Northeast 6 (10) 106 (15) 105 (6) 103 (4) 320 (6) 
 Unknown or non–United States 8 (13) 74 (11) 103 (6) 136 (5) 321 (6) 
Import statusc      
 US acquired 40 (66) 449 (65) 1311 (73) 2153 (74) 3953 (72) 
 International import 2 (3) 10 (1) 28 (2) 36 (1) 76 (1) 
 Unknown 19 (31) 233 (34) 447 (25) 733 (25) 1432 (26) 
Outbreak associated      
 Yes 25 (41) 236 (34) 1272 (71) 2365 (81) 3898 (71) 
 No 31 (51) 375 (54) 354 (20) 376 (13) 1136 (21) 
 Unknown 5 (8) 81 (12) 160 (9) 181 (6) 427 (8) 
Vaccination status      
 Vaccinated 3 (5) 391 (57) 1391 (78) 2245 (77) 4030 (74) 
  1 dose MMR 1 (33) 244 (62) 75 (5) 102 (5) 422 (10) 
  2 doses MMR 2 (67) 74 (19) 1064 (76) 1711 (76) 2851 (71) 
  3 doses MMR 1 (<1) 42 (3) 89 (4) 132 (3) 
  Unknown number of MMR doses 72 (18) 210 (15) 343 (15) 625 (16) 
 Unvaccinated 49 (80) 135 (20) 126 (7) 171 (6) 481 (9) 
 Unknown 9 (15) 166 (24) 269 (15) 506 (17) 950 (17) 
Parotitis      
 Yes 50 (82) 537 (78) 1537 (86) 2481 (85) 4605 (84) 
 No 2 (3) 30 (4) 55 (3) 79 (3) 166 (3) 
 Unknown 9 (15) 125 (18) 194 (11) 362 (12) 690 (13) 
Orchitisd      
 Yes 1 (3) 4 (1) 11 (1) 46 (3) 62 (2) 
 No 25 (71) 291 (71) 691 (73) 1176 (72) 2183 (72) 
 Unknown 9 (26) 114 (28) 244 (26) 412 (25) 779 (26) 
Deafness      
 Yes 1 (<1) 9 (<1) 10 (<1) 
 No 39 (64) 423 (61) 1127 (63) 1902 (65) 3491 (64) 
 Unknown 22 (36) 269 (39) 658 (37) 1011 (35) 1960 (36) 
Meningitis      
 Yes 1 (<1) 2 (<1) 3 (<1) 
 No 49 (80) 493 (71) 1295 (73) 2174 (74) 4011 (73) 
 Unknown 12 (20) 199 (29) 490 (27) 746 (26) 1447 (27) 
Encephalitis      
 Yes 1 (<1) 1 (<1) 2 (<1) 
 No 49 (80) 491 (71) 1294 (72) 2177 (75) 4011 (73) 
 Unknown 12 (20) 200 (29) 492 (28) 744 (25) 1448 (27) 
Hospitalized      
 Yes 8 (13) 32 (5) 30 (2) 40 (1) 110 (2) 
 No 41 (67) 508 (73) 1374 (77) 2341 (80) 4264 (78) 
 Unknown 12 (20) 152 (22) 382 (21) 541 (19) 1087 (20) 
No. (%) Mumps Patients by Age Group, y
<1 (n = 61)1–4 (n = 692)5–10 (n = 1786)11–17 (n = 2922)Total (N = 5461)
Year      
 2015 30 (4) 44 (2) 97 (3) 171 (3) 
 2016 17 (28) 196 (28) 846 (47) 1270 (43) 2329 (43) 
 2017 14 (23) 185 (27) 518 (29) 1047 (36) 1764 (32) 
 2018 14 (23) 142 (21) 204 (11) 245 (8) 605 (11) 
 2019 16 (26) 139 (20) 174 (10) 263 (9) 592 (11) 
Sex      
 Male 35 (57) 409 (59) 946 (53) 1634 (56) 3024 (55) 
 Female 26 (43) 280 (40) 835 (47) 1280 (44) 2421 (44) 
 Unknown 3 (<1) 5 (<1) 8 (<1) 16 (<1) 
Race and ethnicity      
 Asian/Pacific Islander, non-Hispanica 19 (31) 152 (22) 703 (39) 1187 (41) 2061 (38) 
 White, non-Hispanic 15 (25) 167 (24) 397 (22) 618 (21) 1197 (22) 
 Hispanic 11 (18) 140 (20) 289 (16) 436 (15) 876 (16) 
 African American, non-Hispanic 3 (5) 39 (6) 63 (4) 162 (6) 267 (5) 
 Other, non-Hispanic 1 (2) 10 (1) 31 (2) 57 (2) 99 (2) 
 American Indian/Alaskan Native, non-Hispanic 8 (<1) 16 (<1) 24 (<1) 
 Unknown 12 (20) 184 (27) 295 (17) 446 (15) 937 (17) 
Regionb      
 South 28 (46) 259 (37) 1004 (56) 1526 (52) 2817 (52) 
 West 12 (20) 131 (19) 385 (22) 803 (27) 1331 (24) 
 Midwest 7 (11) 122 (18) 189 (11) 354 (12) 672 (12) 
 Northeast 6 (10) 106 (15) 105 (6) 103 (4) 320 (6) 
 Unknown or non–United States 8 (13) 74 (11) 103 (6) 136 (5) 321 (6) 
Import statusc      
 US acquired 40 (66) 449 (65) 1311 (73) 2153 (74) 3953 (72) 
 International import 2 (3) 10 (1) 28 (2) 36 (1) 76 (1) 
 Unknown 19 (31) 233 (34) 447 (25) 733 (25) 1432 (26) 
Outbreak associated      
 Yes 25 (41) 236 (34) 1272 (71) 2365 (81) 3898 (71) 
 No 31 (51) 375 (54) 354 (20) 376 (13) 1136 (21) 
 Unknown 5 (8) 81 (12) 160 (9) 181 (6) 427 (8) 
Vaccination status      
 Vaccinated 3 (5) 391 (57) 1391 (78) 2245 (77) 4030 (74) 
  1 dose MMR 1 (33) 244 (62) 75 (5) 102 (5) 422 (10) 
  2 doses MMR 2 (67) 74 (19) 1064 (76) 1711 (76) 2851 (71) 
  3 doses MMR 1 (<1) 42 (3) 89 (4) 132 (3) 
  Unknown number of MMR doses 72 (18) 210 (15) 343 (15) 625 (16) 
 Unvaccinated 49 (80) 135 (20) 126 (7) 171 (6) 481 (9) 
 Unknown 9 (15) 166 (24) 269 (15) 506 (17) 950 (17) 
Parotitis      
 Yes 50 (82) 537 (78) 1537 (86) 2481 (85) 4605 (84) 
 No 2 (3) 30 (4) 55 (3) 79 (3) 166 (3) 
 Unknown 9 (15) 125 (18) 194 (11) 362 (12) 690 (13) 
Orchitisd      
 Yes 1 (3) 4 (1) 11 (1) 46 (3) 62 (2) 
 No 25 (71) 291 (71) 691 (73) 1176 (72) 2183 (72) 
 Unknown 9 (26) 114 (28) 244 (26) 412 (25) 779 (26) 
Deafness      
 Yes 1 (<1) 9 (<1) 10 (<1) 
 No 39 (64) 423 (61) 1127 (63) 1902 (65) 3491 (64) 
 Unknown 22 (36) 269 (39) 658 (37) 1011 (35) 1960 (36) 
Meningitis      
 Yes 1 (<1) 2 (<1) 3 (<1) 
 No 49 (80) 493 (71) 1295 (73) 2174 (74) 4011 (73) 
 Unknown 12 (20) 199 (29) 490 (27) 746 (26) 1447 (27) 
Encephalitis      
 Yes 1 (<1) 1 (<1) 2 (<1) 
 No 49 (80) 491 (71) 1294 (72) 2177 (75) 4011 (73) 
 Unknown 12 (20) 200 (29) 492 (28) 744 (25) 1448 (27) 
Hospitalized      
 Yes 8 (13) 32 (5) 30 (2) 40 (1) 110 (2) 
 No 41 (67) 508 (73) 1374 (77) 2341 (80) 4264 (78) 
 Unknown 12 (20) 152 (22) 382 (21) 541 (19) 1087 (20) 
a

1787 mumps cases occurred among patients aged <18 y in a large outbreak in a Marshallese community in Arkansas during 2016–2017.11 

b

Geographic regions are defined according to US Census classifications.

c

International imported case defined as a case that resulted from exposure to mumps outside the United States; US acquired is defined as a case occurring in someone who had not traveled outside the United States in the 25 d before onset of parotitis or other complications or had known exposure to mumps in the United States.

d

Proportions were calculated among male patients.

Of pediatric mumps patients ≥1 year of age, 75% were vaccinated with at least 1 dose of MMR, 8% were unvaccinated, and 17% had unknown vaccination status. Among patients ≥1 year of age with known vaccination status and number of doses received (72%), most (84%) were up to date on MMR doses; 74% of 1- to 4-year-olds had received at least 1 dose of MMR and 86% of 5- to 17-year-olds had received at least 2 doses of MMR (Fig 5).

FIGURE 5

Pediatric mumps patients by number of MMR doses received: United States, 2015–2019 (N = 5461); 18-year-olds were included for comparison.

FIGURE 5

Pediatric mumps patients by number of MMR doses received: United States, 2015–2019 (N = 5461); 18-year-olds were included for comparison.

Of 4771 (87%) patients with information on parotitis, 97% experienced parotitis. Seventy-five (1%) patients experienced at least 1 complication. Orchitis was the most frequently reported complication and was reported in 2% of males (median age = 14 years, range: 0–17): 46 (3%) postpubertal males (>10 years) and 16 (1%) prepubertal males (≤10 years), including 1 case in an infant <1 year old. Of male patients ≥1 year of age with orchitis and known vaccination status (66%), 31 (66%) were up to date on MMR vaccination. Deafness was reported in 10 (<1%) patients with a median age of 14 years (range: 7–17). Vaccination status was known for 4 of the patients, and of those, 1 patient was up to date on MMR vaccination. There were 3 (<1%) cases of meningitis, in a 10-year-old, a 13-year-old, and a 17-year-old, all female. The 10- and 13-year-olds were fully vaccinated with 2 doses of MMR, and the 17-year-old was vaccinated but the number of MMR doses was unknown. There were 2 (<1%) cases of encephalitis, in a 1-year-old male and a 17-year-old female, both of whom were up to date on MMR vaccination (Table 2).

TABLE 2

Hospitalization and Complications of Pediatric Mumps Patients by Number of MMR Doses Received: United States, 2015–2019

Unvaccinated1 Dose≥2 DosesVaccinated With Unknown No. DosesUnknown Vaccination StatusNo. Cases/Totala (%)
Hospitalized, n (%) 19 (17) 29 (26) 37 (34) 15 (14) 10 (9) 110/4374 (3) 
Days hospitalized, median (range) 2 (1–7) 3 (1–8) 2 (1–10) 3 (1–5) 2.5 (1–5) — 
Complication, n (%)       
 Any complication 17 (23) 6 (8) 32 (43) 7 (9) 13 (17) 75/5461 (1) 
 Orchitisb 16 (26) 3 (5) 28 (45) 6 (10) 9 (15) 62/2245 (3) 
 Deafness 1 (10) 2 (20) 1 (10) 6 (60) 10/3501 (<1) 
 Meningitis 2 (67) 1 (33) 3/4014 (<1) 
 Encephalitis 1 (50) 1 (50) 2/4013 (<1) 
Unvaccinated1 Dose≥2 DosesVaccinated With Unknown No. DosesUnknown Vaccination StatusNo. Cases/Totala (%)
Hospitalized, n (%) 19 (17) 29 (26) 37 (34) 15 (14) 10 (9) 110/4374 (3) 
Days hospitalized, median (range) 2 (1–7) 3 (1–8) 2 (1–10) 3 (1–5) 2.5 (1–5) — 
Complication, n (%)       
 Any complication 17 (23) 6 (8) 32 (43) 7 (9) 13 (17) 75/5461 (1) 
 Orchitisb 16 (26) 3 (5) 28 (45) 6 (10) 9 (15) 62/2245 (3) 
 Deafness 1 (10) 2 (20) 1 (10) 6 (60) 10/3501 (<1) 
 Meningitis 2 (67) 1 (33) 3/4014 (<1) 
 Encephalitis 1 (50) 1 (50) 2/4013 (<1) 

—, not applicable.

a

Total was calculated among cases with known status.

b

Proportions were calculated among male patients.

Of 4374 (80%) patients with information on hospitalization, 110 (3%) were hospitalized, with a median hospital stay of 2 days (range: 1–10) (Table 2). The median age of hospitalized patients was 7 years (range: 0–17). Of hospitalized patients who were ≥1 year of age and had known vaccination status and number of doses received (78%), 69% were up to date on MMR vaccination for their age group. No deaths were reported.

Since 2007, pediatric mumps cases have represented an important burden of mumps in the United States, accounting for approximately one-third of all reported mumps cases; since 2016, pediatric mumps cases have been reported in most states each year. The majority of pediatric patients with mumps were up to date with their recommended MMR vaccination. Although the age group with the highest incidence was college-aged young adults, consistent with the largest outbreaks during this time occurring on university campuses,19  median annual incidence was still higher among children and adolescents versus adults.

Experts have suggested 2 main reasons for 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.20  Increasing incidence with increasing age, correlating with likely increasing time since vaccination, supports the hypothesis of potential waning immunity against mumps infection after vaccination. Researchers in some epidemiological or modeling studies have suggested that vaccine-derived immune protection against mumps wanes by early adulthood.21,22  However, the results presented in this study reveal vaccinated individuals can become susceptible sooner than young adulthood. The plateau in cases at ∼10 years of age, or ∼5 years after the second MMR dose, is consistent with immunologic studies that reveal mumps antibodies start to decrease within the first year after vaccination with the second dose23  and decline to near baseline levels (ie, return to antibody levels before vaccination with a second dose of MMR) 10 years after vaccination for children vaccinated with the second dose at age 4 to 6 years (against both vaccine and wild-type genotype G strains).24  Second, several studies have revealed that, although vaccine-induced antibodies neutralize wild-type virus, the vaccine-induced immune response is notably lower against the circulating wild-type strains (predominately genotype G in the United States) than against the vaccine strain (genotype A).2426  One study among children revealed neutralizing antibody titers to genotype G mumps strain were approximately one-half those of the vaccine strain,24  and researchers in another study among young adults found genotype G–neutralizing antibody titers were sixfold lower.26 

We report that the majority of pediatric mumps cases were sporadic, except during 2016–2017. During peak years, mumps epidemiology is primarily influenced by large outbreaks that occur in close contact settings. A large outbreak in a close-knit Marshallese community in Arkansas in 2016–201711  resulted in non-Hispanic Asian and/or Pacific Islander being the most frequently reported ethnicity and race during 2015–2019. On college campuses, outbreaks are often associated with groups of students who participate in large gatherings or social groups (eg, Greek life, sports teams). For this reason, findings of studies on mumps waning immunity that use epidemiological data without accounting for outbreak setting or contact rate should be interpreted with caution, because young adults are more likely to be at an increased risk for exposure than children and adolescents through notably more close contacts during large events and intense close contact behaviors that facilitate transmission of mumps. The sudden increase in cases among 18-year-olds (shown in Fig 4, for comparison) can skew the data toward the appearance that young adults are more susceptible to disease versus at higher risk for exposure.

Although mumps was a leading cause of acquired unilateral sensorineural hearing loss and aseptic meningitis among children in the prevaccine era,27,28  these complications, as well as other mumps complications, are now relatively rare among pediatric patients in the United States. The low frequency of complications is likely due to a high rate of vaccination among pediatric mumps patients in the United States in the vaccine era.29  However, as shown here, complications still occurred in vaccinated children. The most commonly reported complication was orchitis, mostly in postpubertal males, although orchitis still occurred in prepubescent males as well, including an infant. The rate of 3% of orchitis among mostly vaccinated postpubertal males in this study is consistent with an average rate of 5% orchitis among vaccinated postpubertal males, compared with ∼30% of unvaccinated postpubertal males.6,8,2931 

During 1998–2017, >90% of children in the United States had received at least 1 dose of MMR by age 35 months32 ; among adolescents 13 to 17 years of age in 2019, >90% had received ≥2 doses.33  Despite this high coverage, cases have been consistently reported in most states since 2016, mostly among people who were vaccinated. Furthermore, only 1 in 50 pediatric mumps cases with known import status were associated with international travel. This suggests that mumps is endemic in the United States. Mumps is therefore different from the other 2 diseases prevented by the MMR vaccine, measles and rubella, both of which are eliminated in the United States. Most measles cases or outbreaks result from disease acquired while traveling abroad and then spread in communities with low vaccination coverage.34 

In 2020, geographically widespread mumps transmission has continued across the United States despite coronavirus disease 2019 (COVID-19) lockdowns and other COVID-19 prevention measures, with 32 US states reporting 142 cases during April 1 through December 31, 2020.35  With continued transmission and decreases and delays in MMR vaccination among children during the COVID-19 pandemic,36  there is a risk that mumps cases and outbreaks among children and adolescents will increase, along with a potential increase in mumps complications, once regular activities and in-person learning resume.

There are several limitations to this study. Although mumps is a nationally notifiable disease, cases and complications may have been underreported. Clinicians may lack suspicion of mumps when a patient is fully vaccinated, even if presenting with parotitis,12  or may not suspect mumps in cases with mumps complications in the absence of parotitis. A study of medical records at Children’s Healthcare of Atlanta revealed that among children and adolescents presenting to the emergency department with parotitis during 2007–2017, <5% were tested for mumps, and of these, 19% were positive for mumps.37  Obtaining a positive laboratory test for diagnosis may be challenging in vaccinated patients and also lead to underreporting. Failure to detect mumps RNA through reverse transcription polymerase chain reaction (RT-PCR) in buccal swabs or immunoglobulin M (IgM) through serological tests in vaccinated patients is likely, because viral loads are lower and the IgM response is often undetectable, transient, or delayed in these individuals.38  Given this, clinicians should not rule out mumps because of a negative laboratory result. Another limitation was the completeness of data in NNDSS. Missing or unknown data for some key variables, including vaccination status, number of doses received, outbreak-associated, import status, or hospitalization ranged from 8% to 26%. Additionally, NNDSS does not provide information on outbreaks or which outbreak a case is associated with, so further details regarding outbreaks or how large outbreaks influenced the epidemiology could not be studied.

Mumps has largely been controlled in the general US population for several decades; most clinicians have never seen patients with mumps and may be unaware that most mumps cases in the United States currently occur among fully vaccinated persons. Since 2007, one-third of reported US mumps cases occurred in children and adolescents, the majority of whom were vaccinated. Mumps vaccination remains the best tool to protect children and adolescents against mumps and mumps complications. However, 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. Appropriate timing and collection technique of specimens is needed for accurate results. The parotid gland should be massaged for 30 seconds before buccal swab collection. A buccal swab specimen should be collected for RT-PCR if it has been ≤3 days since parotitis onset. A buccal swab specimen and a serum specimen for IgM detection should be collected if it has been >3 days since parotitis onset.39  Suspect mumps cases should be reported to the local health department to further investigate potential links to other mumps cases and outbreaks to help identify cases and prevent outbreaks.

FUNDING: No external funding.

COMPANION PAPER: A companion to this article can be found online at www.pediatrics.org/cgi/doi/10.1542/peds.2021-052761.

Ms Shepersky conceptualized and designed the study, conducted data analyses, drafted the initial manuscript, and reviewed and revised the manuscript; Dr Marlow conceptualized and designed the study, drafted the initial manuscript, and reviewed and revised the manuscript; Dr Marin critically reviewed and revised the manuscript for intellectual content; Dr Zhang and Ms Pham conducted data analyses and reviewed and revised the manuscript; and all authors approved the final manuscript as submitted and agree to be accountable for all aspects of the work.

The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.

     
  • COVID-19

    coronavirus disease 2019

  •  
  • CSTE

    Council of State and Territorial Epidemiologists

  •  
  • IgM

    immunoglobulin M

  •  
  • MMR

    measles, mumps, and rubella

  •  
  • NNDSS

    National Notifiable Diseases Surveillance System

  •  
  • RT-PCR

    reverse transcription polymerase chain reaction

1
Rubin
SA
.
Mumps vaccines
. In:
Plotkin
SA
,
Orenstein
WA
,
Offit
PA
,
Edwards
KM
, Eds.
Plotkin's Vaccines. Seventh Edition
.
Philadelpha, PA
:
Elsevier
;
2018
:
663
688
2
Barskey
AE
,
Glasser
JW
,
LeBaron
CW
.
Mumps resurgences in the United States: a historical perspective on unexpected elements
.
Vaccine
.
2009
;
27
(
44
):
6186
6195
3
Centers for Disease Control (CDC)
.
Mumps--United States, 1985-1988
.
MMWR Morb Mortal Wkly Rep
.
1989
;
38
(
7
):
101
105
4
Centers for Disease Control (CDC)
.
Measles prevention: recommendations of the Immunization Practices Advisory Committee (ACIP)
.
MMWR Morb Mortal Wkly Rep
.
1989
;
36
(
S-9
):
1
18
5
Hopkins
RS
,
Jajosky
RA
,
Hall
PA
, et al;
Centers for Disease Control and Prevention (CDC)
.
Summary of notifiable diseases--United States, 2003
.
MMWR Morb Mortal Wkly Rep
.
2005
;
52
(
54
):
1
85
6
Dayan
GH
,
Quinlisk
MP
,
Parker
AA
, et al
.
Recent resurgence of mumps in the United States
.
N Engl J Med
.
2008
;
358
(
15
):
1580
1589
7
Kutty
PK
,
McLean
HQ
,
Lawler
J
, et al
.
Risk factors for transmission of mumps in a highly vaccinated population in Orange County, NY, 2009-2010
.
Pediatr Infect Dis J
.
2014
;
33
(
2
):
121
125
8
Nelson
GE
,
Aguon
A
,
Valencia
E
, et al
.
Epidemiology of a mumps outbreak in a highly vaccinated island population and use of a third dose of measles-mumps-rubella vaccine for outbreak control--Guam 2009 to 2010
.
Pediatr Infect Dis J
.
2013
;
32
(
4
):
374
380
9
Marin
M
,
Marlow
M
,
Moore
KL
,
Patel
M
.
Recommendation of the Advisory Committee on Immunization Practices for use of a third dose of mumps virus-containing vaccine in persons at increased risk for mumps during an outbreak
.
MMWR Morb Mortal Wkly Rep
.
2018
;
67
(
1
):
33
38
10
Albertson
JP
,
Clegg
WJ
,
Reid
HD
, et al
.
Mumps outbreak at a university and recommendation for a third dose of measles-mumps-rubella vaccine - Illinois, 2015–2016
.
MMWR Morb Mortal Wkly Rep
.
2016
;
65
(
29
):
731
734
11
Fields
VS
,
Safi
H
,
Waters
C
, et al
.
Mumps in a highly vaccinated Marshallese community in Arkansas, USA: an outbreak report
.
Lancet Infect Dis
.
2019
;
19
(
2
):
185
192
12
Cataldi
JR
,
O’Leary
ST
,
Marlow
MA
, et al
.
Pediatricians’ knowledge and practices related to mumps diagnosis and prevention [published online ahead of print August 25, 2021]
.
J Pediatr
.
doi:10.1016/j.jpeds.2021.08.036
13
Council of State and Territorial Epidemiologists
.
Revision of the surveillance case definition for mumps
.
14
Council of State and Territorial Epidemiologists
.
Public health reporting and national notification for mumps
.
15
Council of State and Territorial Epidemiologists
.
Public health reporting and national notification for mumps
.
16
National Center for Health Statistics
.
Vintage 2019 postcensal estimates of the resident population of the United States (April 1, 2010, July 1, 2010-July 1, 2019), by year, county, single-year of age (0, 1, 2., 85 years and over), bridged race, Hispanic origin, and sex
.
17
National Center for Health Statistics
.
Estimates of the April 1, 2010 resident population of the United States, by county, single-year of age (0, 1, 2, …, 85 years and over), bridged race, Hispanic origin, and sex
.
18
United States Census Bureau
.
Census regions and divisions of the United States
.
19
Clemmons
NS
,
Redd
SB
,
Gastañaduy
PA
,
Marin
M
,
Patel
M
,
Fiebelkorn
AP
.
Characteristics of large mumps outbreaks in the United States, July 2010-December 2015
.
Clin Infect Dis
.
2019
;
68
(
10
):
1684
1690
20
Plotkin
SA
.
Commentary: mumps vaccines: do we need a new one?
Pediatr Infect Dis J
.
2013
;
32
(
4
):
381
382
21
Lewnard
JA
,
Grad
YH
.
Vaccine waning and mumps re-emergence in the United States
.
Sci Transl Med
.
2018
;
10
(
433
):
eaao5945
22
Vygen
S
,
Fischer
A
,
Meurice
L
, et al
.
Waning immunity against mumps in vaccinated young adults, France 2013
.
Euro Surveill
.
2016
;
21
(
10
):
30156
23
Seagle
EE
,
Bednarczyk
RA
,
Hill
T
, et al
.
Measles, mumps, and rubella antibody patterns of persistence and rate of decline following the second dose of the MMR vaccine
.
Vaccine
.
2018
;
36
(
6
):
818
826
24
Rubin
SA
,
Qi
L
,
Audet
SA
, et al
.
Antibody induced by immunization with the Jeryl Lynn mumps vaccine strain effectively neutralizes a heterologous wild-type mumps virus associated with a large outbreak
.
J Infect Dis
.
2008
;
198
(
4
):
508
515
25
Rubin
SA
,
Link
MA
,
Sauder
CJ
, et al
.
Recent mumps outbreaks in vaccinated populations: no evidence of immune escape
.
J Virol
.
2012
;
86
(
1
):
615
620
26
Rasheed
MAU
,
Hickman
CJ
,
McGrew
M
, et al
.
Decreased humoral immunity to mumps in young adults immunized with MMR vaccine in childhood
.
Proc Natl Acad Sci USA
.
2019
;
116
(
38
):
19071
19076
27
Mizushima
N
,
Murakami
Y
.
Deafness following mumps: the possible pathogenesis and incidence of deafness
.
Auris Nasus Larynx
.
1986
;
13
(
suppl 1
):
S55
S57
28
Rubin
S
,
Eckhaus
M
,
Rennick
LJ
,
Bamford
CG
,
Duprex
WP
.
Molecular biology, pathogenesis and pathology of mumps virus
.
J Pathol
.
2015
;
235
(
2
):
242
252
29
Orlíková
H
,
Malý
M
,
Lexová
P
, et al
.
Protective effect of vaccination against mumps complications, Czech Republic, 2007–2012
.
BMC Public Health
.
2016
;
16
:
293
30
Centers for Disease Control and Prevention (CDC)
.
Update: mumps outbreak - New York and New Jersey, June 2009-January 2010 [published correction appears in MMWR Morb Mortal Wkly Rep. 2010;59(19):594]
.
MMWR Morb Mortal Wkly Rep
.
2010
;
59
(
5
):
125
129
31
Havlíčková
M
,
Limberková
R
,
Smíšková
D
, et al
.
Mumps in the Czech Republic in 2013: clinical characteristics, mumps virus genotyping, and epidemiological links
.
Cent Eur J Public Health
.
2016
;
24
(
1
):
22
28
32
Centers for Disease Control and Prevention (CDC)
.
Vaccination coverage for selected diseases among children aged 19–35 months, by race, Hispanic origin, poverty level, and location of residence in metropolitan statistical area: United States, selected years 1998–2017
.
Available at: https://www.cdc.gov/nchs/data/hus/2018/031.pdf. Accessed December 2, 2020
33
Elam-Evans
LD
,
Yankey
D
,
Singleton
JA
, et al
.
National, regional, state, and selected local area vaccination coverage among adolescents aged 13–17 years - United States, 2019
.
MMWR Morb Mortal Wkly Rep
.
2020
;
69
(
33
):
1109
1116
34
Fiebelkorn
AP
,
Redd
SB
,
Gastañaduy
PA
, et al
.
A comparison of postelimination measles epidemiology in the United States, 2009–2014 versus 2001–2008
.
J Pediatric Infect Dis Soc
.
2017
;
6
(
1
):
40
48
35
Centers for Disease Control and Prevention
.
National notifiable diseases surveillance system, weekly tables of infectious disease data
.
Available at: https://wonder.cdc.gov/nndss/nndss_weekly_tables_menu.asp. Accessed February 22, 2021
36
Santoli
JM
,
Lindley
MC
,
DeSilva
MB
, et al
.
Effects of the COVID-19 pandemic on routine pediatric vaccine ordering and administration - United States, 2020
.
MMWR Morb Mortal Wkly Rep
.
2020
;
69
(
19
):
591
593
37
Reddy
LM
,
Bloch
D
,
Mallino
A
, et al
.
Upward trends of parotitis and mumps in Atlanta over a decade
.
Glob Pediatr Health
.
2020
;
7
:
2333794X20968676
38
Rota
JS
,
Rosen
JB
,
Doll
MK
, et al
.
Comparison of the sensitivity of laboratory diagnostic methods from a well-characterized outbreak of mumps in New York City in 2009
.
Clin Vaccine Immunol
.
2013
;
20
(
3
):
391
396
39
Centers for Disease Control and Prevention
.
Strategies for the control and investigation of mumps outbreaks
.

Competing Interests

POTENTIAL CONFLICT OF INTEREST: The authors have indicated they have no potential conflicts of interest to disclose.

FINANCIAL DISCLOSURE: The authors have indicated they have no financial relationships relevant to this article to disclose.

Supplementary data