Vaccine 29 (2011) 9551–9556 Contents lists available at SciVerse ScienceDirect Vaccine jou rn al h om epa ge: www.elsevier.com/locate/vaccine Transmission of mumps virus from mumps-vaccinated individuals to close contacts Ewout B. Fanoy a , Jeroen Cremer b , José A. Ferreira c , Sabine Dittrich b,d , Alies van Lier b , Susan J.H. Hahné b , Hein J. Boot b , Robert S. van Binnendijk b,∗ a Municipal Health Service “Midden-Nederland”, Zeist, The Netherlands b Centre for Infectious Disease Control, National Institute of Public Health, and the Environment, Bilthoven, The Netherlands c Expertise Centre for Methodology and Information Services, National Institute of Public, Health and the Environment, Bilthoven, The Netherlands d European Public Health Microbiology Training Program (EPIET/EUPHEM), European, Centre for Disease Prevention and Control (ECDC), Stockholm, Sweden a r t i c l e i n f o Article history: Received 23 March 2011 Received in revised form 15 September 2011 Accepted 25 September 2011 Available online 5 October 2011 Keywords: Mumps MMR Viral transmission Vaccination PCR Oral fluid a b s t r a c t During a recent mumps epidemic in the Netherlands caused by a genotype D mumps virus strain, we investigated the potential of vaccinated people to spread mumps disease to close contacts. We com- pared mumps viral titers of oral fluid specimens obtained by quantitative PCR from vaccinated (n = 60) and unvaccinated (n = 111) mumps patients. We also investigated the occurrence of mumps infection among the household contacts of vaccinated mumps patients. We found that viral titers are higher for unvaccinated patients than for vaccinated patients during the 1st 3 days after onset of disease. While no symptomatic cases were reported among the household contacts (n = 164) of vaccinated mumps patients (n = 36), there were cases with serological evidence of asymptomatic infection among vaccinated house- hold contacts (9 of 66 vaccinated siblings). For two of these siblings, the vaccinated index patient was the most probable source of infection. We conclude that, in this particular outbreak, the risk of a close contact becoming infected by vaccinated patients was small, but present. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Mumps epidemics have occurred in many countries despite national mumps vaccination programs, attacking both unvacci- nated and vaccinated individuals [1–3]. In the Netherlands, the combination vaccine against measles, mumps, and rubella (MMR) was introduced in 1987 in the Dutch National Immunization Pro- gram (NIP) for all children aged fourteen months and nine years. The two-dose MMR vaccination coverage has been consistently above 93% [4]. There was no widespread mumps among unvac- cinated people until the incidence of mumps in the Netherlands suddenly increased in August 2007 [5]. We investigated several hundred clinical cases among people residing in regions where vac- cination coverage is considerably lower (due to religious reasons) than it is nationwide. However, clinical mumps infections of people with documented MMR vaccination histories were also reported ∗ Corresponding author at: Centre for infectious Disease Control, National Insti- tute of Public Health and the Environment, P.O. 3720 BA Bilthoven, The Netherlands. Tel.: +31 0 30 274 3582; fax: +31 0 30 274 4418. E-mail address: Rob.van.Binnendijk@rivm.nl (R.S. van Binnendijk). during this epidemic. Both vaccinated and unvaccinated patients resided mainly in the same geographic areas. Previous studies have demonstrated that the virus can be cultured from oropharyngeal specimens obtained from infected unvaccinated patients up to 9 days after the onset of parotitis [6,7]. As mumps disease is transmitted by airborne respiratory droplets, the viral mumps titers in oral fluid can be considered an impor- tant parameter in characterizing the infectiousness of a mumps patient [8–11]. However, there are very few data available about viral shedding, most particularly of vaccinated mumps patients. The extent to which vaccinated individuals can contribute to viral transmission during an outbreak is not well known [8,12,13]. Some studies have shown that one dose of mumps vaccine is less effec- tive than two doses of the vaccine in conferring protection against infection [14]. The recent mumps epidemic in the Netherlands gave us an opportunity to assess viral shedding by determining the viral titer in oral fluid specimens with real-time PCR. We used the viral titer as a parameter to express the infectiousness of a patient in relation to vaccination status and the duration since last mumps vaccination. Furthermore, to assess virus transmission by vaccinated mumps patients, we checked the household con- tacts of vaccinated mumps patients for clinical symptoms or high 0264-410X/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.vaccine.2011.09.100