Clinical mumps vaccine efficacy

Mumps: an Update on Outbreaks, Vaccine Efficacy, and Genomic Diversity

Mumps is an acute viral infection characterized by inflammation of the parotid and other salivary glands. Persons with mumps are infectious from 2 days before through 5 days after parotitis onset, and transmission is through respiratory droplets. Despite the success of mumps vaccination programs in the United States and parts of Europe, a recent increase in outbreaks of mumps virus infections among fully vaccinated populations has been reported. Although the effectiveness of the mumps virus component of the measles-mumps-rubella (MMR) vaccine is suboptimal, a range of contributing factors has led to these outbreaks occurring in high-vaccination-coverage settings, including the intensity of exposure, the possibility of vaccine strain mismatch, delayed implementation of control measures due to the timeliness of reporting, a lack of use of appropriate laboratory tests (such as reverse transcription-PCR), and time since last vaccination. The resurgence of mumps virus infections among previously vaccinated individuals over the past decade has prompted discussions about new strategies to mitigate the risk of future outbreaks. The decision to implement a third dose of the MMR vaccine in response to an outbreak should be considered in discussions with local public health agencies. Traditional public health measures, including the isolation of infectious persons, timely contact tracing, and effective communication and awareness education for the public and medical community, should remain key interventions for outbreak control. Maintaining high mumps vaccination coverage remains key to U.S. and global efforts to reduce disease incidence and rates of complications.

A path-specific SEIR model for use with general latent and infectious time distributions

Most current Bayesian SEIR (Susceptible, Exposed, Infectious, Removed (or Recovered)) models either use exponentially distributed latent and infectious periods, allow for a single distribution on the latent and infectious period, or make strong assumptions regarding the quantity of information available regarding time distributions, particularly the time spent in the exposed compartment. Many infectious diseases require a more realistic assumption on the latent and infectious periods. In this article, we provide an alternative model allowing general distributions to be utilized for both the exposed and infectious compartments, while avoiding the need for full latent time data. The alternative formulation is a path-specific SEIR (PS SEIR) model that follows individual paths through the exposed and infectious compartments, thereby removing the need for an exponential assumption on the latent and infectious time distributions. We show how the PS SEIR model is a stochastic analog to a general class of deterministic SEIR models. We then demonstrate the improvement of this PS SEIR model over more common population averaged models via simulation results and perform a new analysis of the Iowa mumps epidemic from 2006.

Mumps vaccine performance among university students during a mumps outbreak

BACKGROUND

The largest reported mumps outbreak at a US college in 19 years occurred in 2006 at a Kansas university with a 2-dose measles-mumps-rubella (MMR) vaccination policy. We assessed vaccine performance and mumps risk factors, including the possibility of waning vaccine protection.

METHODS

Case students were compared with a cohort of the university's approximately 19,000 undergraduates. The secondary attack rate for clinical mumps was determined among roommates exposed to case students. Time from receipt of the second dose of MMR vaccine was compared between case students and roommates without mumps.

RESULTS

Coverage with > or =2 dose of MMR vaccine was > or =95% among 140 undergraduate case students and 444 cohort students. The secondary attack rate for clinical mumps among roommates who had received 2 doses of vaccine ranged from 2.2% to 7.7%, depending on the case definition. Compared with roommates without mumps, case students were more likely (odds ratio, 2.46; 95% confidence interval, 1.25-4.82) to have received their second dose of MMR vaccine > or =10 years earlier. The odds of being a case student increased with each 1-year increase in time from receipt of the second dose of MMR vaccine (odds ratio, 1.36; 95% confidence interval, 1.10-1.68) among case students and roommates aged 18-19 years but not among those aged > or =20 years. Students aged 18-19 years had a higher risk of mumps (risk ratio, 3.14; 95% confidence interval, 1.60-6.16), compared with students aged > or =22 years; women living in dormitories had increased risk of mumps (risk ratio, 1.95; 95% confidence interval, 1.01-3.76), compared with men not living in dormitories.

CONCLUSION

High 2-dose MMR coverage protected many students from developing mumps but was not sufficient to prevent the mumps outbreak. Vaccine-induced protection may wane. Similar US settings where large numbers of young adults from wild-type naive cohorts live closely together may be at particular risk for mumps outbreaks.

Immune responses to mumps vaccine in adults who were vaccinated in childhood

BACKGROUND

In a mumps outbreak in the United States, many infected individuals were adults who had received 2 doses of mumps vaccine. The persistence of cellular immunity to mumps vaccine has not been defined.

METHODS

This was an observational, nonrandomized cohort study evaluating cell-mediated and humoral immunity to mumps in 10 vaccinated and 10 naturally immune adults. Mumps-specific T cell activation and interferon (IFN)-gamma production were measured using lymphoproliferative and flow cytometry assays, and mumps immunoglobulin (Ig) G was measured using enzyme-linked immunosorbent assay.

RESULTS

T cell immunity to mumps was high in both groups; 70% of vaccinated and 80% of naturally immune individuals had a positive (> or =3) stimulation index (SI) (P = 1.0). The mean percentages of mumps-specific CD4+ T cells that expressed CD69 and produced IFN-gamma were equivalent in the 2 groups: 0.06% and 0.12%, respectively (P = .11). The mean SIs in the groups were also equivalent, although IFN-gamma concentrations from cultures stimulated with mumps antigen were higher in naturally immune adults than in vaccinated adults (P < or = .01). All adults were positive for mumps IgG.

CONCLUSION

T and B cell immunity to mumps was detected in adults at least 10 years after immunization. Except for IFN-gamma release, responses in vaccinated adults paralleled those observed in naturally immune individuals.

Mumps vaccination coverage and vaccine effectiveness in a large outbreak among college students--Iowa, 2006

Following implementation of a routine childhood two-dose measles-mumps-rubella vaccination strategy, mumps disease levels dropped dramatically in the US and an elimination goal was set for 2010. However, a 2006 epidemic involved >5700 cases nationwide, with many reported among fully vaccinated college students. In an outbreak in two Iowa colleges, we investigated: (1) vaccination coverage using electronic records verified by provider records and (2) vaccine effectiveness assessed by comparison of dose-specific attack rates. Mumps was classified as typical (parotitis/orchitis) or atypical (parotid tenderness or submandibular/sublingual adenitis). Two-dose mumps vaccination coverage was 90% both for the student population (2128/2363) and case-students (97/108). Two-dose vaccine effectiveness was 76-88% with no significant difference for attack rates between one and two doses. Among two-dose vaccine recipients, 74% of the population (1482/2009) and 79% of the case-students (75/95) had received the second dose >10 years before. A large mumps outbreak occurred despite high two-dose vaccination coverage in a population most of whom had received the second dose >10 years before. Two-dose vaccine effectiveness was similar to previous one-dose estimates. Further studies are needed to examine the persistence of two-dose mumps vaccine-induced immunity and to determine whether US mumps elimination can be achieved with the current vaccination strategy.

Mumps

Mumps is a common childhood infection caused by the mumps virus. The hallmark of infection is swelling of the parotid gland. Aseptic meningitis and encephalitis are common complications of mumps together with orchitis and oophoritis, which can arise in adult men and women, respectively; other complications include deafness and pancreatitis. Clinical diagnosis can be based on the classic parotid swelling; however, this feature is not present in all cases of mumps and can also occur in various other disorders. Laboratory diagnosis is based on isolation of virus, detection of viral nucleic acid, or serological confirmation (generally presence of IgM mumps antibodies). Mumps is vaccine-preventable, and one dose of mumps vaccine is about 80% effective against the disease. Routine vaccination has proven highly effective in reducing the incidence of mumps, and is presently used by most developed countries; however, there have been outbreaks of disease in vaccinated populations. In 2005, a large epidemic peaked in the UK, and in 2006 the American midwest had several outbreaks. In both countries, the largest proportion of cases was in young adults. In the UK, susceptible cohorts too old to have been vaccinated and too young to have been exposed to natural infections were the primary cause of the mumps epidemic. In the USA, effectiveness and uptake in combination appear not to have been sufficient to obtain herd immunity for mumps in populations such as college students.

Effectiveness of previous mumps vaccination during a summer camp outbreak

OBJECTIVES

Mumps is a vaccine-preventable disease that may cause outbreaks. In July 2005, an outbreak of mumps occurred during a children's summer camp in upstate New York. An investigation was initiated to describe the cases and evaluate vaccine effectiveness.

METHODS

A retrospective cohort study was conducted among 541 children from the United States and abroad who attended a 1- or 2-month overnight summer camp. Patients with mumps were interviewed; serologic analysis was conducted for 6 case patients. Vaccine effectiveness was calculated by retrospective review of immunization records for 507 attendees who were eligible for vaccination and had verified immunization history.

RESULTS

Thirty-one camp attendees were identified as having mumps (attack rate: 5.7%); 5 (83%) of 6 patients tested had positivity for mumps immunoglobulin M. Of the 507 participants (including 29 patients) with available immunization history, 440 (including 16 [87%] patients) were 2-dose recipients of mumps vaccine (attack rate: 3.6%); 46 participants (including 4 [9%] patients) were 1-dose recipients (attack rate: 8.7%); and 21 (including 9 [4%] patients) were unvaccinated (attack rate: 42.9%). Vaccine effectiveness was 92% for 2 doses and 80% for 1 dose.

CONCLUSIONS

Outbreaks of mumps in settings such as summer camps can occur despite high vaccination rates. Vaccine effectiveness for 2 mumps vaccinations was greater than vaccine effectiveness for 1 mumps vaccination. Therefore, recommendation of 2 mumps vaccinations for summer camp participants continues to be appropriate. Control of mumps disease relies on broad vaccination coupled with correct clinical diagnosis and strict control measures.

Mumps outbreak in a highly vaccinated school population: assessment of secondary vaccine failure using IgG avidity measurements

From March to April 2006, an outbreak of mumps occurred in Gyeonggi, Korea. The aim of this study was to describe and discriminate between primary and secondary vaccine failure in a highly vaccinated population for mumps using IgG avidity testing. Fifteen clinical mumps cases occurred among 41 students. Among these 15 patients, 11 vaccinated patients were considered secondary vaccine failures with high IgG titers and a high avidity index (AI, > or =32%); an unvaccinated patient was considered to have primary infection with high IgG titers and low AI, and three vaccinated patients were considered as other infections with low IgG titers and low AI. Among 26 unaffected students, 5 vaccinated patients were retrospectively diagnosed as sub-clinical infection with high IgG titers and high AI; the remaining students had low IgG titers and low AI except for one previously infected student. The results of this study show that secondary vaccine failure played an important role in this mumps outbreak. Therefore, booster immunization for mumps should be considered in immunized adolescents to prevent further outbreaks.

Vaccine effectiveness estimates, 2004-2005 mumps outbreak, England

As vaccinated children approach adolescence, immunity wanes, which may contribute to outbreaks.

The United Kingdom and United States have recently experienced large outbreaks of mumps, which raises concerns about vaccine effectiveness. The effectiveness of the mumps component of the measles, mumps, rubella (MMR) vaccine was estimated using the screening method. In England from January 2004 through March 2005, 312 cases of mumps were reported in children eligible to have received 2 doses of MMR vaccine. Of these children, 52 (16.7%) had received 1 dose of MMR vaccine, and 97 (31.1%) had received 2 doses. Vaccine effectiveness was 88% (95% confidence interval [CI] 83%–91%) for 1 dose and 95% (95% CI 93%–96%) for 2 doses. The effectiveness of 1 dose declined from 96% (95% CI 81%–99%) in 2-year-olds to 66% (95% CI 30%–83%) in 11- to 12-year-olds, and the effectiveness of 2 doses declined from 99% (95% CI 97%–99.5%) in 5- to 6-year-olds to 86% (95% CI 74%–93%) in 11- to 12-year-olds (p<0.001 for 1 or 2 doses). Waning immunity may contribute to mumps outbreaks in older vaccinated populations.

Estimation of vaccine efficacy and the vaccination threshold

This paper considers the effect of imperfect vaccination in a susceptible-infected-removal (SIR) epidemic model. The minimum proportion of the population that needs to be vaccinated to prevent a major epidemic depends on the vaccine efficacy and the basic reproductive rate for the SIR model, allowing for imperfect and variable vaccination. Martingale theory is used to derive estimates and associated standard errors for these parameters. Asymptotic properties of the resulting estimators are investigated. Data for a mumps outbreak are used as an illustrative example.

Zur Schätzung der Schutzwirkung der Influenzaimpfung aus Surveillancedaten

The continuous antigenic drift of influenza viruses requires annual adaptation of the vaccine. Protection depends largely on the match of the variants represented in the vaccine with the viruses actually known to be in circulation and may differ considerably from season to season. Therefore studies to assess the efficacy and effectiveness of the vaccine are conducted rather sporadically on an annual basis and it would be desirable to make use of routinely available data from surveillance programs. We compared two different approaches: (1) the "screening method" where cases are identified from laboratory data and controls are taken from data on vaccination rates and (2) a second method that uses the same cases, but controls were influenza-negative individuals with influenza-like illness (also identified from laboratory data). The sensitivity of the methods to confounders that were considered as relevant was tested with a simulation. Both methods were applied to the data of the German influenza surveillance data of the season 2004/2005. The estimated effectiveness over all age groups was rather low with both methods, but comparable with other estimations from the literature. We observed differences in certain age groups between the methods as well as large differences between particular age groups within one method. Possible explanations are random variations due to low numbers in age strata and other influences not yet considered. Therefore the estimations should be interpreted with care; however, relative comparisons among seasons may still be meaningful.

The effectiveness of the mumps component of the MMR vaccine: a case control study

In 1998/1999, an outbreak of mumps occurred among children of a religious community in North East London. A case control study was conducted to assess the effectiveness of the mumps component of the MMR vaccine. One hundred and sixty-one cases of mumps were identified and 192 controls were selected. Fifty-one percent of cases and 77% of controls had a history at least one MMR vaccination. The observed effectiveness of any MMR vaccination adjusted for age, sex and general practice was 69% (95% CI: 41-84%). This is consistent with the results of other observational studies of mumps containing vaccines, but lower than the immunogenicity of mumps vaccines reported by clinical trials. This discrepancy is because observational studies tend to underestimate vaccine effectiveness, and because immunogenicity is not necessarily an accurate biological marker of vaccine effectiveness. Two doses of vaccine were more effective (88% (95% CI: 62-96%)) than a single dose (64% (95% CI: 40-78%)). The current two-dose vaccination programme remains the best method for controlling mumps infection in the community.

Outbreak of mumps in a vaccinated child population: a question of vaccine failure?

In Belgium, children are immunized against measles-mumps-rubella (MMR) in a two-dose schedule at the age of 15 months and 11 years. Despite these recommendations, epidemics of mumps still occur. During an outbreak of mumps in Bruges (Belgium), 105 cases were registered in seven schools (age group 3-12 years). Lower than optimal vaccination coverage, inadequate vaccination schedule and a combination of primary and/or secondary vaccine failure are considered as possible reasons for the outbreak as described in the article. The role of secondary vaccine failure is highlighted.

A review of licensed viral vaccines, some of their safety concerns, and the advances in the development of investigational viral vaccines

Viral vaccines could be considered among the most important medical achievements of the 20th century. They have prevented much suffering and saved many lives. Although some curative antiviral drugs exist, we desperately depend on efforts by academic, governmental and industrial scientists in the advancement of viral vaccines in the prevention and control of infectious diseases. In the next decade, we hope to see advancement in the development of current and investigational viral vaccines against childhood and adult infections. In this article, we will review the licensed viral vaccines, some of their safety concerns, and the advances in the development of investigational viral vaccines.

Vaccines and immunotherapies for the prevention of infectious diseases having cutaneous manifestations

Although the development of antimicrobial drugs has advanced rapidly in the past several years, such agents act against only certain groups of microbes and are associated with increasing rates of resistance. These limitations of treatment force physicians to continue to rely on prevention, which is more effective and cost-effective than therapy. From the use of the smallpox vaccine by Jenner in the 1700s to the current concerns about biologic warfare, the technology for vaccine development has seen numerous advances. The currently available vaccines for viral illnesses include Dryvax for smallpox; the combination measles, mumps, and rubella vaccine; inactivated vaccine for hepatitis A; plasma-derived vaccine for hepatitis B; and the live attenuated Oka strain vaccine for varicella zoster. Vaccines available against bacterial illnesses include those for anthrax, Haemophilus influenzae, and Neisseria meningitidis. Currently in development for both prophylactic and therapeutic purposes are vaccines for HIV, herpes simplex virus, and human papillomavirus. Other vaccines being investigated for prevention are those for cytomegalovirus, respiratory syncytial virus, parainfluenza virus, hepatitis C, and dengue fever, among many others. Fungal and protozoan diseases are also subjects of vaccine research. Among immunoglobulins approved for prophylactic and therapeutic use are those against cytomegalovirus, hepatitis A and B, measles, rabies, and tetanus. With this progress, it is hoped that effective vaccines soon will be developed for many more infectious diseases with cutaneous manifestations.

Estimating vaccine efficacy using auxiliary outcome data and a small validation sample

In vaccine studies, a specific diagnosis of a suspected case by culture or serology of the infectious agent is expensive and difficult. Implementing validation sets in the study is less expensive and is easier to carry out. In studies using validation sets, the non-specific or auxiliary outcome is measured on each participant while the specific outcome is measured only for a small proportion of the participants. Vaccine efficacy, defined as one minus some measure of relative risk, could be severely attenuated if based only on the auxiliary outcome. Applying missing data analysis techniques could thus correct the bias while maintaining statistical efficiency. However, when the sample size in the validation sets is small and the vaccine is highly efficacious, all specific outcomes are likely to be negative in the validation set in the vaccinated group. Two commonly used missing data analysis methods, the mean score method and multiple imputation, depend on the ad hoc continuity correction when none of the specific outcomes are positive and the normality or log-normality assumption of relative risk, which may not hold when the relative risk is highly skewed, to estimate the confidence interval. In this paper, we propose a Bayesian method to estimate vaccine efficacy and its highest probability density (HPD) credible set using Monte Carlo (MC) methods when using auxiliary outcome data and a small validation sample. Comparing the performance of these approaches using data from a field study of influenza vaccine and simulations, we recommend to use the Bayesian method in this situation.

Evidence based vaccinology

Evidence based vaccinology (EBV) is the identification and use of the best evidence in making and implementing decisions during all of the stages of the life of a vaccine, including pre-licensure vaccine development and post-licensure manufacture and research, and utilization of the vaccine for disease control. Vaccines, unlike most pharmaceuticals, are in a continuous process of development both before and after licensure. Changes in biologics manufacturing technology and changes that vaccines induce in population and disease biology lead to periodic review of regimens (and sometimes dosage) based on changing immunologic data or public perceptions relevant to vaccine safety and effectiveness. EBV includes the use of evidence based medicine (EBM) both in clinical trials and in national disease containment programs. The rationale for EBV is that the highest evidentiary standards are required to maintain a rigorous scientific basis of vaccine quality control in manufacture and to ensure valid determination of vaccine efficacy, field effectiveness and safety profiles (including post-licensure safety monitoring), cost-benefit analyses, and risk:benefit ratios. EBV is increasingly based on statistically validated, clearly defined laboratory, manufacturing, clinical and epidemiological research methods and procedures, codified as good laboratory practices (GLP), good manufacturing practices (GMP), good clinical research practices (GCRP) and in clinical and public health practice (good vaccination practices, GVP). Implementation demands many data-driven decisions made by a spectrum of specialists pre- and post-licensure, and is essential to maintaining public confidence in vaccines.

Mumps caused by an inadequately attenuated measles, mumps and rubella vaccine

PROBLEM

Reports of mumps following measles, mumps and rubella (MMR) immunization.

OBJECTIVE

To determine whether mumps was caused by immunization or whether there was a concurrent epidemic of a wild strain of mumps.

DESIGN AND PARTICIPANTS

Analysis of surveillance data and a cohort study of three schools that participated in the campaign.

OUTCOME MEASURES

Cases of clinical mumps and orchitis, and immunization history and records were reviewed. The MMR vaccine was produced by the Serum Institute of India and contained the Leningrad-Zagreb strain of mumps virus. Four lots were used in the specific immunization campaign.

RESULTS

Sentinel health facility surveillance showed an increase in mumps after two school immunization campaigns in western Suriname and a mass immunization campaign in the same region. There was also an increase in a geographically separate region following a mass campaign with the same vaccine. Three hundred fifteen children from three schools that were targeted in the immunization campaign were interviewed. The attack rate for mumps in those immunized was 15.1%; in those not immunized, the attack rate was 4.7%. In the affected males, the attack rate for orchitis was five of 19 (21%). Assuming 90% protection by the MMR vaccine, the incidence ratio (observed to expected) was 32.

CONCLUSIONS

The mumps outbreak was caused by an inadequately attenuated MMR vaccine. Because this vaccine had not been used in these populations before in Suriname, it was not possible to determine wether the outbreak was due the virulence of the Leningrad-Zagreb mumps strain or due to production problems with one or more specific lots of vaccine. The vaccine was withdrawn from further use.

Efficiency of estimating vaccine efficacy for susceptibility and infectiousness: randomization by individual versus household

In designing vaccine efficacy studies based on the secondary attack rate (SAR) or transmission probability in which both vaccine efficacy for susceptibility, VE(S), and vaccine efficacy for infectiousness, VE(I), are estimated, the allocation of vaccine and placebo within transmission units has an important influence on the efficiency of the study. We compared the following randomization schemes that result in different allocations of vaccine and placebo within two-member households: (1) randomization by individual for a mixed allocation, (2) randomization by transmission unit for concordant allocation, and (3) randomization of only one individual in each transmission unit to either vaccine or placebo. There is a complex interaction among the VE(S), VE(I), and the SAR that determines which allocation of vaccine and placebo within households provides the most information. In general, individual randomization with a mixed allocation of vaccine and placebo is better for estimating both VE(S) and VE(I) than is randomizing by household. However, for estimation of VE(I), at very low SARs and low VE(S), randomization by household is slightly more efficient than randomization by individual.

Estimation of the direct and indirect effects of vaccination

Indirect effects play a major role in the protection afforded by a vaccination programme. In this work we define new measures of direct, indirect and total (direct + indirect) effects of a vaccination programme in terms of the protection they provide to unvaccinated and vaccinated individuals, and to the entire population. We show how these measures can be estimated using data from a vaccine trial or an observational study. The bias and standard errors of these estimates can be evaluated via stochastic simulations. Examples from a mumps outbreak and a (hypothetical) HIV vaccine trial are used to illustrate the estimation of these new measures of vaccination effectiveness.

Analysis of mumps vaccine failure by means of avidity testing for mumps virus-specific immunoglobulin G

To characterize patients with mumps vaccine failure, avidity testing was performed with the Enzygnost Anti-Parotitis Virus/IgG kit using a single-dilution-6 M urea denaturation method. Five groups of patients were tested. Group 1 consisted of 29 patients with primary mumps infections; group 2 was 20 children and adults with a definite history of natural infection; group 3 was 7 patients with a recent mumps vaccination, 1 of whom developed parotid gland swelling and aseptic meningitis; group 4 was 14 patients with mumps vaccine failure; and group 5 was 6 patients with recurrent episodes of parotitis in addition to a history of vaccination. On the basis of the results of groups 1 and 2, an avidity of </=31% was determined to be low, and >/=32% was determined to be high. Avidity maturation from low to high appears to occur around 180 days after the acute illness. The results of group 3 showed that the vaccine-induced immunoglobulin G (IgG) had very low avidity. Among the 14 patients in group 4, 12 patients, including 7 with a positive IgM response, were diagnosed as having secondary vaccine failures. The results of group 5 suggested the possibility that the avidity of the mumps vaccine-induced IgG remains low or borderline. These results showed that secondary mumps vaccine failure occurs not infrequently, even among school age children under condition in which the vaccine coverage is low (i.e., 33% in our study population), and therefore, vaccinees are prone to be exposed to wild-type viruses. Avidity testing should provide information useful for the analysis of mumps virus infections.

Field evaluation of the clinical effectiveness of vaccines against pertussis, measles, rubella and mumps. The Benevento and Compobasso Pediatricians Network for the Control of Vaccine-Preventable Diseases

Beginning in March 1995, in the adjacent provinces of Benevento and Campobasso in Southern Italy, we carried out a sentinel, paediatrician-based surveillance on pertussis, measles, rubella and mumps with the aim of evaluating the health impact of new vaccination programmes and the objectives of describing the time-space trends and estimating the effectiveness of new vaccinations. The study population consisted of 16,500 children attended by 25 paediatricians. The estimated effectiveness of vaccines for pertussis, measles and rubella were close to the expected values, although a very low effectiveness was calculated for the mumps vaccine. The comparison among children vaccinated with various strains showed a diseases odds ratio of 2.5 for the children vaccinated with Rubini strain. The effectiveness of this strain has to be verified in more rigorous settings.

[Mumps vaccines: virological basis]

The prevention of mumps virus infection relies on the application of live, attenuated mumps virus vaccines. The process of attenuation from a wildtype mumps isolate to a safe vaccine has been empirical. A lower degree of attenuation results in solid immunity but carries an increased risk of post-vaccination meningitis due to the vaccine strain. Currently used vaccine strains are highly attenuated and essentially free of vaccine strain induced disease. However, their immunogenicity may be lower than previously reported.

[Mumps epidemiology in Switzerland: results from the Sentinella surveillance system 1986-1993. Sentinella Work Group]

Since 1990, there have been reports of an increasing number of mumps cases in Switzerland, in particular among vaccinated children, and of local outbreaks of mumps. Using data from the Sentinella reporting system, a network of voluntary participating doctors (general practitioners, internists and paediatricians, yearly average: n = 141), trends and factors influencing mumps incidence in the general population were assessed during the last seven years. Following an initial decline in mumps reports, since 1990, there has been a continuous and marked increase in reports from a minimum of 0.7 cases per physician and year in 1989/90 to a near five-fold increase of 3.3 cases in the last reporting period from June-December 1993 (calculated for one year). Half of this increase, which is reflected in a doubling of the number of cases reported in 1986/87, is explained by an increase in cases among vaccinated children. The trend in mumps cases contrasts with that of measles and rubella, where there has been a clear decline in these reports since 1986 (approximately 70-80%). Complications were reported in 75 (4.0%) of the total number of mumps patients (n = 1894); in 2/5 of the cases this was a meningitis, in 1/3 an orchitis. Based on available data on vaccination coverage, the estimated efficacy of the mumps vaccines against parotitis is between 47-77%; this is clearly lower than the corresponding figure for measles (91-97%) and rubella (89-97%) vaccines. The relatively low efficacy against parotitis is mainly due to a protective level of 13-73% of the vaccines containing the Rubini strain. The estimated efficacy of the Rubini vaccines against complications is 50-81%; it is nearly 60-90% if a possible reporting bias is taken into consideration.

CONCLUSIONS

1. The Rubini strain vaccines, which are the most commonly used in Switzerland, seem to have played an important role in the clear increase in mumps cases since 1990. 2. The situation seems more favourable concerning the efficacy against complications of the vaccines used. 3. Our data support the high efficacy of all measles and rubella vaccines. 4. The surveillance of MMR by the Sentinella reporting system provides a useful and effective manner to evaluate the MMR vaccination programme.

[A look back at 2 mumps outbreaks]

Two studies are presented. The first one concerns a mumps outbreak in a kindergarten in Geneva in June 1991. Of 26 children, nine (34.6%) got mumps. Of nine children vaccinated with the Rubini vaccine strain, seven had the disease as opposed to only one of 14 children vaccinated with the Urabe strain. The vaccine efficacy of the Rubini strain was estimated at 22% with a 95% confidence interval of -10% to 45%. The second study concerns a cluster of 112 mumps patients seen by a pediatrician in the Bernese Jura region between September 1992 and May 1993. A case-control study was carried out resulting in a vaccine efficacy estimate of 50% with a 95% confidence interval of -19% to 81%. Of the cases, 51 (45.5%) had been vaccinated against mumps, 50 of them (98%) with the Rubini vaccine strain. Of the controls, 30 (61.2%) had been vaccinated, 86.7% of them with Rubini. Methodological problems of case selection and their possible effects on the estimated vaccine efficacy are discussed. The results of these two studies have been confirmed by more recent investigations. In retrospect, we therefore conclude that small studies can serve as early indicators for epidemiological evidence and that they can be finally integrated into a more complete picture.

Pediatric immunizations

The record of disease prevention in children is an impressive testament to our universal immunization program. However, these successes are being threatened by rates of vaccination in some areas of the country that are substantially less than those seen in the developing world. Unless the pediatric immunization rates are improved, epidemics of other vaccine-preventable diseases will recur, as evidenced by the measles outbreaks. Although the tools needed for disease prevention are available, the means for their delivery are lacking. It is the obligation of us all to immunize the nation's children.

Vaccine safety versus vaccine efficacy in mass immunisation programmes

In community-wide immunisation programmes against childhood infections there is a conflict between the interests of the individual (vaccine safety and efficacy) and the interests of the community (vaccine uptake and level of herd immunity). Studies suggesting that the complication rate is greater with the high efficacy Urabe Am 9 mumps vaccine than with the lower efficacy Jeryl Lynn vaccine, have led to concern about whether the higher efficacy mumps vaccine should be introduced or retained in nationwide mass immunisation programmes. We describe the use of a mathematical model to assess benefits and risks to both individual and community, and illustrate this method by reference to immunisation programmes based on these vaccines. On the basis of current epidemiological data on viral transmission and vaccine coverage in England and Wales, data on vaccine-associated and infection-associated complication rates, and vaccine efficacies estimated from clinical trials, our analyses suggest there is little to choose between the two vaccines, but that overall performance depends on the level of vaccine coverage in a defined population. In community-based programmes, the greater apparent safety of the Jeryl Lynn vaccine (fewer vaccine-induced complications) is offset by the greater apparent efficacy of the Urabe Am 9 vaccine (fewer complications due to natural infection). The findings suggest that it may not always be in the interests of the community to use the vaccine with the lowest complication rate.

Mumps outbreak in a highly vaccinated population

From October 1988 to April 1989, a large mumps outbreak occurred in Douglas County, Kansas. Of the 269 cases, 208 (77.3%) occurred among primary and secondary school students, of whom 203 (97.6%) had documentation of mumps vaccination. Attack rates were highest for students attending junior high school (8.0%), followed by high school (2.0%) and elementary school (0.7%). A retrospective cohort study conducted at one junior high school with an attack rate of 12.9% did not find age at vaccination or type of vaccine received (single or combined antigen) to be risk factors for vaccine failure. Students vaccinated more than 4 years before the outbreak appeared to have a higher attack rate than those vaccinated more recently (relative risk (RR) = 4.3; 95% confidence interval (CI) = 0.6, 30.0); however, this association did not exist when risk was evaluated based on number of vaccine doses received. Students who had documentation of receiving only one dose of vaccine were at greater risk than those who had received two doses (RR = 5.2; 95% CI = 1.0, 206.2). Overall, vaccine effectiveness among Douglas County junior high school students was estimated to be 83% (95% CI = 57%, 94%). These data suggest that mumps vaccine failure and the failure to vaccinate have contributed to the relative resurgence of mumps observed in the United States since 1986. The recent change in immunization policy to recommend a two-dose schedule of measles-mumps-rubella vaccine should help reduce the occurrence of mumps outbreaks in highly vaccinated populations.

Rubella and mumps vaccines

As a fetal infection occurring during early pregnancy, rubella's potential for teratogenicity is unparalleled. In the postnatal period it is a relatively benign disease. Mumps, on the other hand, causes moderate morbidity and occasional mortality. Both infections cause considerable morbidity and disruption in the lives of young people gathered for group activities. Widespread use of safe and effective live attenuated vaccines has dramatically reduced the incidence of rubella, congenital rubella, and mumps in the United States. Nevertheless, significant numbers of young children, especially in areas of urban and rural immigration and poverty, fail to be immunized in a timely fashion; and some adolescents and young adults remain susceptible either because they escaped immunization in childhood or are primary vaccine failures. These individuals remain the source of individual cases and small outbreaks of rubella and mumps. For total eradication of these infections, we need to intensify vaccine efforts and to maintain surveillance efforts for mumps, rubella, and congenital rubella syndrome.

Mumps in the US Army 1980-86: should recruits be immunized?

The US Army's experience with mumps hospitalizations was examined for the years 1980 through 1986. One hundred fifty-two cases among active duty Army soldiers were identified. Mumps rates declined from 3.85 per 100,000 active duty soldiers per year in 1980 to 1.28 in 1985, but an outbreak during 1986 caused rates to jump to 6.65. Attack rates were found to decline dramatically with increasing age or length of military service, with 74 per cent of cases occurring in soldiers with three years or less of service. Rates for Blacks and Whites were similar, but were higher for other minorities. Complications reported were mild. A cost-benefit analysis, assuming all recruits were to be vaccinated, estimated average annual vaccination program costs of $286,789; this figure exceeds average annual reported hospitalized mumps disease costs of $61,525 by a factor of 4.7. Mumps attack rates would have to reach at least 15.0 per 100,000 per year before savings would equal recruit vaccination costs. Failure to show that a vaccine program would be cost-saving may be due to limitations in identifying cases or to the requirement that all recruits be immunized regardless of prior immune status. It is likely that a program to immunize susceptible individuals alone would show benefit.