Mumps outbreaks in vaccinated populations: are available mumps vaccines effective enough to prevent outbreaks?

[Mumps transmission control status and inapparent infection rate among middle and high school students during the 2007-2008 mumps outbreak in Daegu]

OBJECTIVES

This study was performed to investigate the mumps transmission control status and inapparent infection rate among middle and high school students in Daegu City during a mumps outbreak.

METHODS

Nine schools (two middle schools and seven high schools), which reported a number of mumps cases between 2007 and 2008 were selected for investigation. During March-May 2008, a standard questionnaire was distributed to gather information about case identification, instructed isolation measure, isolation status of mumps cases and related factors, and outdoor activities of non-isolated mumps case. Inapparent infection rate was estimated by serum mumps IgM and IgG antibodies status and self-reported mumps symptoms in three of the nine schools.

RESULTS

Among 2,560 respondents, more than half of students answered that they did not receive instructions in mumps transmission control measures during the outbreak. Among the 327 mumps cases identified by the questionnaire, 131 cases (40.1%) were considered as isolated and the isolation rates were significantly different among schools, grades, and gender. Of the non-isolated cases, 88.3% continued attending school. Inapparent mumps infection rates were between 56.3% and 70.2%.

CONCLUSIONS

Mumps transmission control was inadequate to control the mumps outbreak. Although high inapparent infection rate would mitigate the transmission control effect of case isolation, this measure is fundamental for infection control. The reasons of this inadequate status need to be explored to develop an effective intervention strategy.

Mumps virus detection during an outbreak in a highly unvaccinated population in British Columbia

OBJECTIVES

Control measures of mumps involve isolation of those symptomatic or potentially exposed. Recent guidelines have recommended shortening the isolation period from 9 days to 5 days after the onset of parotitis, despite using mainly historical evidence. In British Columbia, mumps circulated in a predominantly unvaccinated population in 2008. We compared laboratory findings between the different vaccination groups and assessed the period of mumps viral detection after onset of parotitis.

METHODS

Demographic and clinical data were collected according to guidelines during the course of the outbreak. Clinical specimens, including buccal swabs, urine, CSF and sera, were collected on a single visit upon presentation for diagnosis. Laboratory diagnosis of mumps was confirmed by either virus detection by PCR and/or isolation in cell culture from clinical specimens, or by serology.

RESULTS

Laboratory testing confirmed mumps on 85 (74%) of 115 cases by virus detection and/or serology. Thirty-nine (78%) of 50 cases had virus detected within the first 5 days after onset of parotitis, with the rate highest in specimens collected early. However, virus could be detected in 5 (56%) of 9 cases after day 5 and up to day 9.

CONCLUSION

Our study questions whether a 5-day isolation period is sufficient to prevent mumps transmission in a susceptible population. Our observations are based on single specimen submission, whereas an optimal study design would entail serial collection after presentation of parotitis, as this reflects true viral shedding. Further investigations are warranted to validate patient isolation guidelines.

MMR vaccination and disease elimination: the Finnish experience

Measles, mumps and rubella (MMR) vaccinations have been included in Finland's national vaccination program as a two-dose schedule since 1982. Owing to the high (>95%) coverage of vaccinations, indigenous MMR diseases were eliminated from Finland by the mid-1990s. In 1982, the incidence of measles, mumps and rubella was 105, 43 and 64 per 100,000 population, respectively, but declined to 0.1 per 100,000 population for all MMR diseases in 1995. Since then, the few cases of measles, mumps and rubella imported annually have not caused any outbreaks. Several research projects that started along with the vaccination campaign have provided important support throughout the program. The vaccine was proven to be safe, immunogenic and effective. Antibody follow-up has revealed that MMR vaccine-induced antibodies wane over time, and concerns have arisen about the continuation of this good situation. High vaccination coverage, enhanced surveillance and preparedness to administer additional doses when needed are key factors for future success. Here we present an overview of MMR vaccinations and the Finnish experience of the MMR disease elimination process, and we describe surveillance activities in the era following elimination in Finland.

Mumps outbreak in the Republic of Moldova, 2007-2008

BACKGROUND

Moldova experienced a nationwide mumps outbreak between 2007 and 2008. Single-dose monovalent mumps vaccination at 15 to 18 months was introduced in 1983, replaced by a 2-dose MMR schedule at age 1 and 6 to 7 years in 2002. We investigated the outbreak to quantify its extent, explore the role of primary and secondary vaccine failure, and provide control recommendations.

METHODS

We analyzed national mumps surveillance and vaccination coverage data to estimate vaccine effectiveness (VE) using the screening method. A retrospective cohort study in 5 educational institutions was conducted to determine age-specific attack rates (ARs) and VE. We compared vaccine strain-specific ARs. Isolation and genotyping of mumps virus strains were performed.

RESULTS

Of 31,142 cases reported during October 2007 and July 2008, 80% were in 15- to 24-year-olds. Of cases with information (66%), 92% were vaccinated once, 4% twice. One-dose mumps VE estimates based on surveillance data over 1997-2001 declined from 91% (95% CI: 88%-92%) in 2-year-olds to 72% (70%-74%) in 15- to 19-year-olds. In the cohort study (n = 1589), VE was -40% (-120% to 20%) for 1 dose. For 2 doses it was 62% (-43% to 90%) in 13- to 15-year-olds. ARs were higher in individuals vaccinated with Urabe strains (43%) than with Leningrad-Zagreb strains (14%, P < 0.001). Mumps virus genotype G5 was identified.

CONCLUSIONS

Low effectiveness of single-dose mumps vaccination was the main cause of the outbreak. Waning immunity may have contributed to this. The risk of mumps in 2-dose vaccinees was low. Other countries in which large population groups have received <2 doses of mumps vaccine may face similar outbreaks.

Correlates of protection induced by vaccination

This paper attempts to summarize current knowledge about immune responses to vaccines that correlate with protection. Although the immune system is redundant, almost all current vaccines work through antibodies in serum or on mucosa that block infection or bacteremia/viremia and thus provide a correlate of protection. The functional characteristics of antibodies, as well as quantity, are important. Antibody may be highly correlated with protection or synergistic with other functions. Immune memory is a critical correlate: effector memory for short-incubation diseases and central memory for long-incubation diseases. Cellular immunity acts to kill or suppress intracellular pathogens and may also synergize with antibody. For some vaccines, we have no true correlates, but only useful surrogates, for an unknown protective response.

Mumps vaccine effectiveness in highly immunized populations

The aim of the study was to investigate effectiveness of mumps MMR component in communities with high MMR coverage. Outbreak-related cases of mumps born between 1995 and 2005 notified to Navarre and Catalonia public health services during the period 2005-2007 were studied. Vaccine effectiveness (VE) and their 95%CI were calculated using the screening method. Of 47 confirmed, 85.1% immunized with at least one dose (1MMR) and 44.9% with two (2MMR). Estimated VE was 85.4% (95%CI: 67.3-93.4) for 1MMR and 88.5% (95%CI: 78.1-93.9) for 2MMR. High 2MMR coverage, improved confirmation techniques and further VE studies with all confirmed cases are needed to prevent further outbreaks.

Mumps outbreak in a highly vaccinated student population, The Netherlands, 2004

In September 2004 a mumps outbreak occurred at an international hotel school in The Netherlands. We investigated this outbreak to identify risk factors for mumps. There were 105 mumps cases (overall mumps attack rate (AR) 12% (95% CI: 10-15%)). The AR for Dutch vaccinated and unvaccinated participants was 12% (95% CI: 10-15%) and 15% (95% CI: 3-42%), respectively. Independent risk factor was mumps contact. Explanations for the relatively high AR among vaccinated participants include primary vaccine failure, waning immunity and incomplete vaccine-induced immunity in the context of high mumps virus exposure in a school party and a crowded boarding school.

Successful seroresponses to measles and rubella following aerosolized Triviraten vaccine, but poor response to aerosolized mumps (Rubini) component: comparisons with injected MMR

Seroresponses to measles, rubella and mumps were evaluated following the injection of MMR II and injection or aerosol administration of Triviraten in young adults. Response to aerosolized Rubini mumps strain was a focus of interest, given robust responses to aerosolized mumps vaccine (Leningrad-Zagreb strain) in a prior study using aerosolized MMR vaccine. The aerosolized Edmonston-Zagreb (EZ) measles vaccine was significantly more immunogenic than injected EZ vaccine, and comparable to results following injected Moraten measles vaccine having twice the dosage. Responses to rubella were comparable in the three MMR study groups. Aerosolized Rubini vaccine was very highly and unexpectedly less immunogenic than either injected Rubini or Jeryl-Lyn strains. The high attenuation of Rubini vaccine appears to have limited its affinity for respiratory tract receptors, which may underlie its lack of clinical effectiveness.

Effectiveness of Jeryl Lynn-containing vaccine in Spanish children

We evaluated the effectiveness of the Jeryl Lynn strain vaccine in a large outbreak of mumps in Navarre, Spain, 2006-2008. Each of the 241 cases of mumps occurring in children over 15 months of age born between 1998 and 2005 was compared with 5 controls individually matched by sex, birth date, district of residence and paediatrician. Vaccination history was obtained blindly from clinical records. Conditional logistic regression was used to obtain the matched odds ratios (ORs), and effectiveness was calculated as 1-OR. Some 70% of cases had received one dose of measles-mumps-rubella vaccine, and 24% had received two doses. Overall vaccine effectiveness was 72% (95% CI, 39-87%). Two doses were more effective (83%; 54-94%) than a single dose (66%; 25-85%). Among vaccinated children, risk was higher in those who had received the first dose after 36 months of age (OR=3.1; 1.2-8.4) and those who had received the second dose 3 or more years before study enrolment (OR=10.2; 1.5-70.7). Early waning of immunity in children after the second dose may contribute to reduced vaccine effectiveness for mumps prevention.