Mumps Vaccine Effectiveness During an Outbreak in New York City Kara Livingston, Jennifer Rosen, Jane Zucker, Christopher Zimmerman NYC Department of Health & Mental Hygiene Bureau of Immunization

Mumps Viral illness Often presents with parotitis Rare complications: orchitis, encephalitis, aseptic meningitis, hearing loss Up to 30% of infections asymptomatic Incubation period: range 12-25d Preventable through vaccination

Mumps Vaccine Vaccine introduced in 1967 Mumps cases in US declined 99.6% after introduction of vaccine Combined measles-mumps-rubella vaccine (MMR) 1st dose age 12m, 2nd dose age 4-6y Outbreaks still occur in vaccinated populations Largest being 2006 outbreak in the mid-West with ~6,000 cases Waning immunity Crowding Decline in vaccine effectiveness

Mumps Vaccine Effectiveness (MVE) Initial clinical trials 95% efficacy of monovalent vaccine MVE calculated in various settings and age groups 1973-1989 MVE estimates One-dose: 75%-91% 2005-2010 MVE estimates One-dose: 64%-88% Two-dose: 83%-92% Hilleman, NEJM 1968; Cohen, EID 2007; Schaffzin, Pediatrics 2007; Marin, Vaccine 2008; Castilla, Vaccine 2009; Dominguez, Vaccine 2010

New York City (NYC) Outbreak NYC experienced an outbreak of mumps in 2009-2010 in a vaccinated population This outbreak afforded an opportunity to assess Risk factors for mumps in households Mumps vaccine effectiveness (MVE)

Confirmed Mumps Cases by Parotitis Onset Date, NYC, July 2009 – July 2010

Methods Cases identified via routine surveillance reported by providers and labs Standard surveillance investigations 9/1/09 – 12/31/09: expanded household investigations Documented vaccination status on household contacts 3/10- 4/10: follow-up calls to collect information on illness status, residence, # of bedrooms

Mumps Case Definitions Surveillance clinical case definition Acute onset, unilateral or bilateral tender, self-limited swelling of parotid or other salivary glands, lasting >2 days, without other apparent cause Clinically compatible illness reported by interviewee at follow-up Sick since 9/09 with doctor diagnosed mumps or cheek swelling lasting > 2 days

Methods: Study definitions Index case The first case identified in household as part of routine surveillance, with earliest onset of symptoms Co-primary case Mumps cases with onset prior to earliest incubation period (< 9 days) after onset of index’s illness Secondary case Mumps cases with onset > 9 days after index’s illness

Methods: Household Exclusion Criteria Initial investigation: excluded if index Lived alone or in dormitory (24) Did not speak English (1) Unreachable (84) Unable/unwilling to provide information on household contacts (285) At follow-up: excluded if unreachable/refused (127) After follow-up: excluded if index didn’t sleep in home (35)

Methods Univariate and multivariate analyses to examine risk factors Age, time from last MMR dose, density Secondary household attack rates (AR) to calculate MVE MVE=([ARunvx-ARvx]/ARunvx)*100% Excluded children age < 5 y (n=342) Children < 5 were excluded from VE calculation based on the epidemiology of mumps which has shown that even in the pre-vaccine era, clinical mumps disease is rare among those under-five years of age In order to be considered valid, doses had to be administered no earlier than 4 days before the first birthday and at least 28 days after a previous MMR dose.

Results: Descriptive Data 311 households Median 7 (2-16) people Median 4 (1-8) bedrooms AR ranged from7%-100% of household 2,176 household residents Median age: 13 (0-85) years 462 (21%) met definition for mumps 311 index, 23 co-primary, 93 secondary, 35 unknown (no onset date) 50% of non-index cases reported via surveillance

Vaccination Status of Household Members by Age Group 89% 74% 88% 89% 4-18 year olds had one or two doses 74% 4-18 year olds had two doses 88% adults 19+ had unknown vaccination history Age Group (years)

Risks for Disease Secondary Cases Total AR (%) Odds Ratio (95% CI) Age group 0-4 years 488 0.0 Referent 5-9 years 17 224 7.6 1.4 (0.6-3.4) 10-14 years 29 311 9.3 3.4 (1.6-7.1) 15-19 year 14 341 4.1 2.7 (1.2-6.1) 20 + years 10 342 2.9 1.6 (0.7-3.4)

Risks for Disease Secondary Cases Total AR (%) Odd Ratio (95% CI) Time from last MMR <5 years 31 660 4.7 Referent 5-10 years 27 348 7.8 1.7 (0.9-3.1) >10 years 6 161 3.7 0.8 (0.3-2.0) Household Density < 2 people/ bedroom 53 951 5.6 > 2 people/ bedroom 37 808 4.6 0.8 (0.5-1.4)

Likelihood of secondary mumps among household contacts by age group Age group (years) # Mumps cases Total household members Odds Ratio* (95% CI) p-value 0-4 488 Referent 5-9 17 224 1.4 (0.6-3.4) 0.4263 10-14 29 311 3.4 (1.6-7.1) 0.0010 15-19 14 341 2.7 (1.2-6.1) 0.0155 20+ 10 342 1.6 (0.7-3.4) 0.2527 *Generalized estimating equations; controlled for household density and time since last MMR

One and Two-Dose Mumps Vaccine Effectiveness # MMR Doses # Mumps cases Total household members AR VE % 95% CI 6 20 0.300 -- 1 116 0.052 82.8 51.8-93.8 2 43 697 0.062 79.4 57.4-90.1 Excludes children age <5y and persons with unknown MMR history

Summary Age was associated with mumps Higher likelihood of mumps among adolescents Did not find an associations between: Time from vaccination and mumps Household density (people/bedroom) Two-dose MVE among household contacts aged > 5y was 79.4% (57.4-90.1)

Limitations MVE for clinical mumps only 44% of secondary cases determined by follow-up report only May not have been equal exposure to disease for all household members Many adults lacked MMR records and so were not included in the analysis Transmission of mumps in schools may have contributed to the high proportion of cases in school aged children.

Conclusions We found MMR vaccine effective at preventing disease Our MVE estimate fell within the range found in other recent studies Higher MMR coverage may have helped prevent this outbreak A better understanding of factors leading to outbreaks and outbreak control measures among vaccinated individuals is needed

Acknowledgments CDC/CSTE Applied Epidemiology Fellowship Kara Livingston, MPH NYC DOHMH Christopher M. Zimmerman, MD, MPH Jane R. Zucker, MD, MSc Jennifer Rosen, MD Kisha Cummings, MPH Margaret Doll, MPH Joseph Egger, PhD, MA Jim Hadler, MD, MPH New York City Call Center BOI Surveillance Unit CDC Gregory Armstrong, MD, MSCE Mumps cases and their families

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