INTRODUTION
Mumps is an acute viral infection of the paramyxovirus family. As its alternative name (infectious parotits) suggests, the infection is charecterized by swelling more commonly bilateral than unilateral of the parotid salivary glands. The incubation period is 14-21 days and is communicable from 6 days before to 9 days after facial swelling is apparent. It can lead to brain inflammation, deafness or sterility.
A stiff neck (benign meningeal sign) occurs in up to 15% of cases but permanent effects are rare. Orchitis, (inflammation of the testicles), usually affects only one side in up to 20% of symptomatic cases in postpubertal males. Sterility is a rare but potential complication, along with hepatitis, oophoritis, myocarditis, thyroiditis and nerve deafness.
Epidemiology
The virus is present throughout the world. About one-third of cases are without symptoms. Children are commonly affected, although when infection does occur in adults, this tends to be noticed because complications are more likely to be unpleasant. Cases usually occur in winter and spring. Transmission is by droplet and direct contact with an infected individual. It is expected that as vaccine uptake increases, cases will tend to occur predominantly in older children.
Treatment
There is no treatment against the virus. Supportive treatment is usually sufficient to minimize the effects of complications.
Public health strategies
Mumps is a potentially distressing illness with some particularly unpleasant side- effects. The disease is not considered eradicable, and has a low priority in terms of public health efforts to control it. Many countries have chosen to limit its effects by immunizing childhood populations. This is particularly important in terms of reducing the disease acquired in adults since their complications may be more severe.
The vaccine is a live attenuated viral vaccine, usually given in combination with measles and rubella vaccines (MMR), but may also be monovalent.
Safety
Following MMR, a fever of 39.40 C or higher develops in approximately 5-15% of susceptible vaccinees, usually beginning 7-12days after vaccination. The fever may last 1-2 days or for as long as 5 days. Transient rashes have also been reported in about 5% of vaccine recipients. Mild parotitis may also be seen rarely in the third week after immunization. The mild measles illness that occurs is not communicable.
GPV policy
Mumps vaccine is not part of the EPI recommended childhood immunization schedule, although dozens of countries use it as MR or MMR.
Special issues
Mumps infection and administration of the vaccine are both known to cause aseptic meningitis in a small proportion of individuals. This process involves an inflammation of the lining of the brain (meninges). The virus has been isolated from the cerebrospinal fluid in natural mumps infection. It is thought the Urabe strain of vaccine causes aseptic meningits in about one in one thousand immunized children, but this may vary from country to country. The Jeryl Lynn strain either cause much less or no aseptic meningitis. Most countries now use MMR vaccine containing the Jeryl Lynn strain, although evidence suggests that the Urabe strain may induce stronger immunit
The Mumps Vaccine
A killed mumps virus vaccine was licensed in the USA in 1948 and used from 1950 through 1978. The vaccine's use was poorly accepted because it induced only short-term (less than one year) immunity, required revaccination, and had a relatively low protective efficacy against clinical mumps in susceptible individuals. Live virus mumps vaccines, containing attenuated virus strains have since been developed in the USA, Japan, USSR, and Switzerland.
Mumps virus strains used for vaccine
At least 10 strains of the mumps virus are in use throughout the world for live attenuated vaccine. The first vaccine strain to be developed, and that most often used, is the Jeryl Lynn strain which was named after the child from whom the virus was isolated. It was developed in the USA by passaging seven times in embryonated hen's eggs and ten times in chick embryo cell cultures At the initial level of attenuation, lower than that used in the final vaccine, the Jeryl Lynn strain produced parotid swelling in some vaccinees what was the indicating that the vaccine strain was not suffficiently attenuated. This parotid swelling was not seen after additional passages at the B level of attenuation. Since December 1967, a live attenuated Jeryl Lynn vaccine has been manufactured and distributed by an American company. It induces seroconversion in at least 97% of children and 93% of adults, whether used alone or in combination with measles and rubella vaccines.
In the USSR in the 1950s, the Leningrad-3 strain was developed by Smrodintsev and Klyachko in guinea pig kidney cell culture, with further passages in Japanese quail embryo cultures. Vaccines based on this strain have been used in the former Soviet Union and other countries.
Leningrad-3 mumps virus was further attenuated in Croatia by adaptation and passages on chick embryo fibroblast cell culture. The new mumps strain has been designated L-Zagreb. This strain is used in Croatia and India.
The Urabe strain of live mumps vaccine was first licensed in Japan and thereafter in Belgium, France, and Italy. It is produced either in the amnion of embryonated hen's eggs or in chick-embryo cell cultures and has been used successfully in Japan and other countries. Its immunogenic properties are similar to those of the Jeryl Lynn strain.
The other strains are used to produce vaccines on a limited local scale. Hoshino, Torii and NKM - 46 strains are said to have characteristics similar to those of the Urabe strain. Mumps vaccine strains have been attenuated on different cell-culture systems and it was originally thought that they are were equally capable of inducing high levels of immunity. Recent observations, however, suggest that some vaccines based on the Rubini strain, approved in 1985 in Switzerland, have lower efficacy than those based on the Jeryl Lynn or Urabe strains. One possible explanation for a low protective efficacy of the Rubini strain may be the high number ( > 30) of passages attained during its attenuation process. Vaccines prepared from various strains may differ in their capacity to cause adverse events; meningitis associated with MMR vaccine containing Urabe strains has led to the withdrawal of Urabe-containing vaccine from several countries.
Forms of live vaccine
Live mumps vaccine are available in monovalent vaccine and in combination with other vaccines. The most popular forms are a trivalent vaccine, (MMR), containing measles, mumps and rubella components, and a bivalent vaccine containing measles and mumps vaccines. Monovalent vaccine is used in Russia and other Newly Independent States. WHO requirements do not specify the minimum amount of vaccine virus that one human dose should contain. Rather this is determined by the National Control Authority. Most countries use at least 1000 CCID50 per dose, but many vaccines often contain higher amounts of the mumps virus. Sorbitol and hydrolized gelatin are used as stabilizers and neomycin is added as a preservative.
Vaccine potency and stability
The assays used for assessing mumps vaccine potency are subject to inter-laboratory variability. A collaborative study, involving 10 European laboratories, assessed the variability of estimates of the potency of all three components of MMR vaccines prepared from different mumps virus strain. While the assay-to assay variation within laboratories was small, overall median variation in potency between laboratories was large. Potency estimates for the mumps component of MMR vaccines showed the greatest variability.
The stability of mumps vaccine at 40 C, 230 C, 370C and 450 C is similar to that of measles vaccine. At 370 C the degradation rates are about 0.01 log10 per day for both components. Half lives are also similar: 4.7 and 5.4 days for measles and mumps components at 450 C, 12 and 13 days at 370 C and 71 and 65 days at 230 C, respectively.
Mumps, or parotis epidemica is a viral infection primarily affecting the salivary glands.Although mostly a mild childhood disease, mumps virus may also affect adults, among whom complications such as meningitis and orchitis are relatively common.Encephalitis and permanent neurological sequelae are rare complications of mumps.In most parts of the world the annual incidence of mumps is in the range of 100–1000 per 100 000 population, with epidemic peaks every two to five years.Peak incidence is found among children five to nine years of age. Natural infection with mumps virus is likely to confer lifelong protection.All commercially available mumps vaccines are based on live, attenuated strains of the virus. Extensive use of these vaccines in industrialized countries has proved them to be safe and efficacious; so far about 500 million doses have been administered. Approximately 120 countries are using mumps vaccine in their national immunization services. Where sustained vaccination has been achieved the incidence of mumps has been significantly reduced. In general, adverse reactions to mumps vaccination are rare and mild.
Large-scale mumps vaccination is recommended in countries with an efficient childhood vaccination programme and sufficient resources to maintain high-level vaccination coverage. In such countries the combination of mumps vaccine with measles, or preferably, measles and rubella vaccines is recommended. National decisions to implement large-scale mumps vaccination should be based on careful cost-benefit analyses. As insufficient childhood vaccination coverage may result in an unfortunate epidemiological shift in the incidence of mumps to older age groups, childhood mumps vaccination should aim at a 80% coverage rate, or higher. In countries with lower childhood coverage rates, mumps vaccination may also be offered to assumed non-immune children 9–12 years of age. WHO recommends making mumps a notifiable disease. If a large proportion of the population remains seronegative for mumps, care should be taken to vaccinate adults considered to be at special risk. Regular serosurveillance will provide information on the susceptibility for mumps in various age groups.
Public health impact
Until recent decades mumps has been a common infectious disease in all parts of the world, with annual incidences ranging from approximately 0.1% – 1%, in certain populations even reaching 6%. In hot climates the disease is endemic throughout the year, whereas in temperate climates incidence peaks in late winter. Mumps is generally a mild, self-limiting disease, although complications such as meningitis, encephalitis or orchitis may occur. Asymptomatic pleocytosis (>5 leucocytes/mm 3 ) of the CSF is found in 50%–60% of mumps patients, whereas symptomatic meningitis is reported in up to 15% of the cases. Meningitis occurs more often in males than in females and adults are at a higher risk than children. Mumps encephalitis without signs of meningitis is reported in 0.02%–0.3% of the cases. Although the case-fatality rate of mumps encephalitis is low (1.4%), permanent sequelae such as deafness occur in about 25% of the cases. Acquired sensorineural deafness caused by mumps is one of the leading causes of deafness in childhood, affecting approximately 5 in 100 000 mumps patients.
Mumps orchitis occurs in 20%–50% of postpubertal males. Both testes are affected in approximately 20% of these cases, but mumps orchitis is rarely associated with permanently impaired fertility. However, a history of mumps orchitis seems to be a risk factor for testicular cancer.
Symptomatic oophoritis and mastitis are relatively uncommon, and apparently without long-lasting consequences for the patients. Acquisition of mumps during the first 12 weeks of pregnancy is associated with a high (25%) incidence of spontaneous abortions, although malformations following mumps virus infection during pregnancy have not been found.
Pancreatitis is reported as a complication in approximately 4% of the cases, but the relationship of mumps disease to diabetes mellitus remains speculative. In the prevaccination era mumps used to be the main cause of viral encephalitis in the United States. According to Swedish estimates, before the introduction of routine vaccination, about 1000 annual cases of mumps meningitis required approximately 20 000 days of hospitalization and resulted in 20 000 to 40 000 days of disability.
In countries where vaccines against mumps were introduced in the late 1960s, the incidence of this disease has dropped by 88% – 99%. Protection against mumps correlates with the presence of specific serum antibodies, which persist for more than 10 years following vaccination. However, with insufficient vaccination coverage resurgent outbreaks have occurred, as was the case in the United States between 1985 and 1987 when a fivefold increase in mumps incidence was recorded.
The increase was accompanied by a shift in peak incidence from children aged five to nine years to children and adolescents aged 10–19 years. The largest increase was seen in the age group 15–19 years, which accounted for more than one-third of the reported total number of cases in this period. This resurgence was a consequence of low vaccine coverage in the cohort of children born between 1967 and 1977.There was no evidence of waning immunity in vaccinated persons.
Furthermore, the states that required proof of mumps immunity for school attendance had incidence rates only one-tenth of the states without such vaccination requirements, strongly suggesting that failure to vaccinate, rather than vaccine failure, was theprime reason for the observed epidemiological shift.
By the year 2000, approximately 120 countries or regions had included vaccination against mumps in their national immunization services, the vast majority combining mumps with measles and rubella vaccines (MMR). However, in the African Region only Egypt has included vaccination against mumps, and in the South-East Asia Region, only Singapore, Thailand and Brunei have done so. In these two regions mumps incidence remains high, with epidemic peaks every two to five years, mostly affecting children five to nine years of age.
The pathogen and disease
The mumps virus belongs to the family Paramyxoviridae. The average size of the spherical mumps virus is 200 nm. A host cell-derived lipid membrane encloses the nucleocapsid containing a single-stranded RNA genome. Embedded in the membrane are protruding glycoproteins such as hemagglutinin and neuraminidase. The viral(V) antigen is also associated with the membrane. Antibodies to the V antigen occur in late infection whereas antibodies to the nucleocapsid (the soluble (S) antigen) are detectable in early stages. Simple and reliable enzyme-linked immunosorbent assays(ELISAs) specific for antibodies to mumps virus are widely available.
Mumps virus replicates in a variety of cell cultures as well as in embryonated hens’ eggs. For primary isolation in routine diagnostic virology, monkey kidney, human embryonic kidney or HeLa cell cultures are used. The presence of mumps virus in a cell culture may be detected by the Haemagglutination Inhibition Assay(HAI) test.
Humans are the only known natural host for mumps virus. The virus is spread via direct contact or by airborne droplets from the upper respiratory tract. It requires more intimate contact for transmission than the measles or varicella viruses.The incubation time averages 16–18 days with a range of two to four weeks.
Typically, mumps begins with non-specific symptoms such as myalgia, headache, malaise and low-grade fever that within a day are followed by the characteristic unilateral or bilateral swelling of the parotid glands. Within one to three days,other salivary glands are visibly affected in approximately 10% of the cases.
After about one week, fever and glandular swelling disappear, and unless complications occur, the illness resolves completely. In approximately 30% of the cases, infection passes with non-specific symptoms only or without symptoms at all.There is no specific therapy.
Protective immune response
Only one serotype of mumps virus exists. In general, natural infection confers lifelong protection against the virus, but recurrent mumps attacks have been reported. It is not known whether boosting by circulating wild virus in the community is a prerequisite for lifelong immunity against this disease. Clinically diagnosed mumps is regarded as evidence of immunity. Serological confirmation of immunity is based on the demonstration of specific serum IgG using common immunoassays. In immune individuals IgA antibodies secreted from the nasopharyngeal mucosa exhibit neutralizing activity against mumps virus and are regarded as a first-line defence.
Studies in several different countries have demonstrated that the seroprevalence of antibodies to mumps virus often reaches approximately 90% in individuals 14–15 years of age. Hence, in such populations, persons born 20 years or more before the implementation of large-scale childhood vaccination may be regarded as naturally immune. However, the adult seroprevalence may differ considerably between countries, and in some areas the protection rate may be as low as 50%.
Low seroprevalences among the adult population may reflect real differences in transmission rates of mumps virus, a lengthy interval since the most recent outbreak, or differences in sampling or laboratory technique. Assumed susceptible persons may be vaccinated without preceding laboratory testing.
The justification for vaccine control
Although deaths due to mumps are rare, the disease can impose a substantial economic burden on society due to the fact that, in unvaccinated communities, almost every person may get infected and run a relatively high risk of complications.
Studies in industrialized countries have shown the incorporation of effective mumps vaccines into national immunization services to be highly cost-beneficial. In Austria, the benefit-cost ratio was 3.6 for routine childhood vaccination using the Jeryl Lynn mumps vaccine. In Israel, the benefit-cost ratio was 5.9 for routine immunization with MMR vaccine at 15 months of age. A South African study indicates that adding mumps (and rubella) vaccines to the measles vaccination programme may be very cost effective.
Generally, effective vaccines against mumps and high vaccination coverage may reduce the incidence of this disease to insignificant levels. For example, in Finland in 1996, mumps was eliminated following 14 years of programmatic vaccination. Accompanying surveillance revealed no persistent sequelae or deaths attributable to the vaccine. Furthermore, in spite of a few imported cases no secondary cases have been reported, indicating a sustained immunity in the community.
Mumps vaccine candidates
A killed mumps virus vaccine that was licensed in the United States in 1948 and used from 1950 to 1978, found little acceptance because it induced only short-term immunity of low protective efficacy. Since then, live, attenuated mumps virus vaccines have been developed in Japan, the Russian Federation, Switzerland and the United States. The vaccines are scheduled for either one or two doses, the first given at 12–15 months of age and the second at 9–12 years of age. They are available as monovalent, bivalent measles-mumps (MM) vaccines and trivalent measles-mumps-rubella (MMR) vaccines. WHO requirements do not specify the minimum amount of vaccine virus that one human dose should contain. Rather,this is determined by the national control authority of the country where the vaccine is produced. Most of these vaccines contain more than 1000 cell-culture infective doses of attenuated mumps virus per dose. Sorbitol and hydrolysed gelatine are used as stabilisers and neomycin is added as a preservative to the mumps vaccines.The vaccines are cold-chain-dependent, and need to be protected from light both before and after reconstitution. Reconstituted vaccine must be discarded if it is not used within eight hours.
Different attenuated strains of mumps virus are used for the development of live vaccine. After its introduction in the United States in 1967, the Jeryl Lynn strain was recommended for routine use in 1977. The vaccine was developed by passaging the virus in embryonated hens’ eggs, then in chick embryo cell cultures. By 1992, it had been administered to approximately 135 million children and adults around the world. In 1995, the number of reported mumps cases in the United States was only about 1% of the 1968 figures. Studies in industrialized countries show that a single dose of the Jeryl Lynn strain mumps vaccine leads to seroconversion rates of 80%–100%. Children given one dose of the MMR vaccine containing the Jeryl Lynn component are in 73% of the cases still seropositive after 10.5 years. Similarly, following a two-dose schedule administered five years apart, 86% are seropositive four years after the second dose. Outbreak-based studies from the United States have demonstrated that the protective efficacy of the Jeryl Lynn strain against clinical mumps ranges from 75% to 91%. However, the risk of mumps seemed to increase with the number of years following vaccination, suggesting some waning of protective immunity.
The incidence of vaccine-associated cases of aseptic meningitis ranges from 0.1–1 per 100 000 doses of the Jeryl Lynn mumps vaccine.The Leningrad-3 vaccine strain developed in the former Soviet Union is propagated in guinea-pig kidney cell culture and further passaged in Japanese quail embryo culture. Approximately 8–11 million doses are produced annually. This vaccine has achieved seroconversion rates of 89%–98% in children one to seven years of age and protective efficacy ranging from 92% to 99%. Furthermore, a trial involving 113 967 children aged 1–12 years, demonstrated 96.6% protective efficacy when used as urgent prophylaxis during a Russian mumps outbreak. The outbreak was arrested within one month, and a clear positive economic effect was demonstrated.
Passive surveillance and retrospective reviews indicate an incidence of 20–100 cases of aseptic meningitis per 100 000 doses of MM vaccine based on the Leningrad-3 strain. The Leningrad-3 strain has been further attenuated in Croatia by adaptation to chick embryo fibroblast cell culture. The new strain designated L-Zagreb is used in Croatia,India and Slovenia. Studies of L-Zagreb in Croatia revealed protective properties equivalent to those seen with the Leningrad-3 strain and also the incidence of vaccine associated aseptic meningitis remained largely the same (2–90 per 100 000 doses of MMR).
Live mumps vaccine based on the Urabe strain was first licensed in Japan and then in France, Belgium and Italy. The Urabe strain is produced either in the amnion of embryonated hens’ eggs or in chick embryo cell cultures. It has been used successfully in several countries and since 1979 more than 60 million persons have received this vaccine. Seroconversion rates in children aged 12–20 months range from 92%–100%, and in children nine months of age the corresponding range is 75%–99%.
A comparative study in the United Kingdom using either the Jeryl Lynn or the Urabe strain in combination with measles and rubella vaccines showed that four years after a single dose of MMR vaccine the seropositivity rates were 85% for the Urabe strain and 81% for the Jeryl Lynn strain. In Canada, the corresponding rates five to six years after a single dose MMR vaccine were 93% and 85% respectively.
A possible association of the Urabe strain with vaccine-induced meningitis has resulted in its withdrawal from some countries. Studies up to 1993 identified an incidence of approximately 100 cases of aseptic meningitis per 100 000 doses of MMR containing the Urabe mumps strain. However, the rates differed by manufacturer.
The Rubini strain was first licensed in Switzerland in 1985. It was developed by passage in a human diploid cell line, serial passaging in embryonated hens’ eggs and then adapted to the MRC-5 human diploid cell line. Recent observations with the vaccine based on the Rubini strain suggest that this vaccine has lower efficacy than those based on the Jeryl Lynn or Urabe strains. A three-year study in Switzerland showed that the Rubini strain conferred only 6.3% protection whereas the Urabe and Jeryl Lynn based vaccines achieved 73.1% and 61.6% efficacy respectively.In another study the corresponding figures were 12.4%, 75.8% and 64.7%.
An explanation for these poor results may be the high number of passages (>30) resulting in an overly attenuated vaccine strain. Furthermore, the manufacturer of the Rubini strain vaccine now recommends a second dose at four to six years of age.Data on the protective efficacy of this schedule are currently not available.Attenuated mumps virus strains that are used on a limited scale only include the Hoshino, Torii and NKM-46 strains. They are reported to possess immunogenic properties similar to the Urabe strain.
Adverse reactions
In general, adverse reactions to mumps vaccination are rare and mild. However, moderate fever may occur rarely and aseptic meningitis has been reported in 0.1–100 per 100 000 vaccinees, depending on the vaccine strain used. Vaccine-associated meningitis resolves spontaneously in less than one week without any sequelae.
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Contraindications
There are few contraindications to mumps vaccination. As with all live attenuated vaccines, mumps vaccine should not be administered to individuals with advanced immune deficiency or immunosuppression. Pregnant women should not receive mumps vaccine, and pregnancy should be avoided for three months after vaccination (fetal damage has, however, not been documented). Allergy to vaccine components such as neomycin and gelatine is contraindicative.
WHO position on mumps vaccines
Although the currently available mumps vaccines are of variable quality in terms of adverse reactions and protective efficacy, there is ample evidence that the best of these vaccines are highly efficacious and safe. Where included in successful national immunization services, these vaccines have led to dramatic reductions in the incidence of mumps. Furthermore, primary mumps vaccination is easily adapted to the national vaccination programmes, and does not interfere significantly with simultaneously administered vaccines, for example the recommended combination with rubella and measles-containing vaccines. On the other hand, live vaccines’ dependency on cold-chain conditions is a disadvantage for their use, particularly in low-income countries with hot climates.
In view of the moderate morbidity and the low mortality of this disease, its socioeconomic impact is essential when deciding on the priority of mumps vaccination in national immunization services. Assessment of that impact requires careful evaluation of disease burden and costs associated with purchase of the vaccine and vaccination, including the economic impact of possible adverse effects.
Countries considering inclusion of mumps vaccination into their national immunization service should be able to offer the vaccine to all children aged 12–15 months. The addition of mumps vaccine to the measles vaccination programme, using the MM or MMR combined vaccines is logistically sound and will increase the benefit-cost ratio. The MMR combination is strongly encouraged where it is affordable.
Serological studies show that vaccine response rates are excellent from the age of 12 months and, for the Urabe vaccine strain, high titres are achieved from the age of 9 months. When aiming at mumps control MMR vaccination at 9–15 months of age and coverage rates of 80% or more would be appropriate. Coverage rates below 70%–80% may result in an epidemiological shift. This because reduced, but not interrupted, circulation of mumps virus in the community is likely to leave a large proportion of adults without immunity from natural infection. Therefore, if only a relatively low coverage can be achieved, the introduction of a second vaccine dose at the age of 9–12 years should be considered. If a large proportion of the population remains seronegative for mumps, the vaccine may be provided to adults at special risk, such as health workers, teachers and military personnel.
High-quality mumps vaccines generally confer substantial protection and will reduce the costs associated with patient care and lost working days due to mumps. WHO therefore recommends the use of such vaccines in all countries with well-functioning childhood vaccination programmes, provided that sustained high-level coverage is afforded and that reduction of mumps is a public health priority.
Mumps vaccination should be followed by registration of immunization coverage. In order to reduce underestimation by passive surveillance, mumps should be made a notifiable disease.
Public health strategies
Mumps, a generalized infection caused by a virus of the Paramyxovirus family, primarily affects the salivary glands, causing parotitis. Although mostly responsible for a mild childhood disease, this virus may also affect adults, among whom complications such as orchitis are relatively common. Meningitis, encephalitis and permanent neurological sequelae are rare complications of mumps at any age.
In most parts of the world the annual incidence of mumps is in the range 100–1000 per 100 000 population, and epidemics occur at intervals of two to five years. The incidence of the disease peaks among children aged five to nine years.Natural infection with mumps virus is thought to confer lifelong protection. Theoretically, the disease could be eradicated, but public health efforts to control it are given low priority. Many countries have chosen to limit its effects by immunizing populations of children. This is particularly important in reducing the disease acquired in adulthood, when the complications may be comparatively severe.
WHO perspective
The currently available mumps vaccines vary in their protective efficacy and the adverse reactions they induce but there is ample evidence that most of them are highly effective and safe. Primary mumps immunization can easily be incorporated into successful national immunization services, where these vaccines have led to dramatic reductions in the incidence of the disease.
All the commercially available mumps vaccines are based on live attenuated strains of the virus. So far, approximately 500 million doses of mumps vaccine have been administered, mainly in the industrialized world. In 2002, 118 countries or territories reported using mumps vaccine in their national immunization services, mainly in combination with measles and rubella vaccines.
The introduction of mumps vaccine should be considered only in countries that have established, or are in the process of establishing, adequate programmes for the elimination of measles and the control of congenital rubella syndrome. This is because WHO accords the latter objectives a higher priority than mumps control. In such countries the combination of mumps vaccine with measles and rubella vaccines is recommended. National decisions to implement large-scale mumps immunization should be based on careful cost-benefit analyses, including the comparative analysis of mumps control versus the control of other vaccine-preventable diseases in the countries concerned.
Mumps vaccines are available as monovalent, bivalent measles–mumps (MM) and trivalent measles–mumps–rubella (MMR) vaccines. WHO does not specify the minimum amount of vaccine virus that one human dose should contain. This is determined by the national regulatory authority of the country where the vaccine is produced. The vaccine requires an effective cold chain for transportation and must be protected from light both before and after reconstitution. Reconstituted vaccine that remains unused for six hours must be discarded. Countries considering the inclusion of mumps vaccine in their national immunization services should set targets for elimination or control and should design their immunization strategies accordingly.
Special issues
Mumps control: The control of mumps can be achieved through high routine coverage with an effective mumps-containing vaccine administered at 12–18 months of age. Children immunized with most mumps vaccines at the age of 12 months or older have excellent serological response rates. Programmes should aim at infant coverage of more than 90%. Low immunization coverage may reduce the number of cases in infants but fails to interrupt circulation of the mumps virus in the community.
Furthermore, there is an associated epidemiological shift, involving a paradoxical increase in the number of cases in adults who are without immunity from natural infection. The addition of mumps vaccine to the measles vaccination service by using the MMR combined vaccine is logistically sound. The use of the MMR combination is strongly encouraged where it is epidemiologically indicated and affordable.
Mumps elimination: Strategies for achieving mumps elimination should include:
Achieving high (more than 90%) coverage with a first dose of mumps-containing
vaccine at the age of 12–18 months;
Ensuring a second opportunity for immunization;
Conducting catch-up immunization of susceptible cohorts.
A second opportunity is not required in countries where coverage with the first dose is sufficiently high (i.e. more than 90%). If a second opportunity is needed it can be given by administering a second routine dose or by conducting periodic catch-up campaigns. If an initial catch-up campaign is implemented, the target age group should be that in which susceptibility to mumps is highest. In most unvaccinated populations a majority of children acquire mumps infections before reaching the age of 10 years.
Reactogenicity and immunogenicity:
In general, adverse reactions to mumps vaccine are rare and mild. The most common adverse reactions are parotitis and low-grade fever. However, moderate fever sometimes occurs and aseptic meningitis has been reported at widely different frequencies. Countries intending to use mumps vaccine during mass campaigns should give special attention to planning. The mumps vaccine strain should be carefully selected, health workers should be trained on expected rates of adverse events following immunization, guidelines should be provided on the monitoring, investigation and management of such events, and community advocacy and health education should be carried out.
Because meningitis may occur as an adverse event during mass campaigns, particular care must be exercised in selecting a suitable vaccine strain that has low meningitis reaction rates. Most licensed mumps vaccine strains are highly efficacious. High seroconversion rates after immunization have been reported. In contrast, the Rubini strain exhibits low seroconversion and effectiveness rates and is not recommended by WHO for use in national immunization services.