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The MMR vaccine is a mixture of live attenuated viruses, administered via injection for immunization against measles, mumps and rubella. It is generally administered to children around the age of one year, with a booster dose before starting school (i.e. age 4/5). It is widely used around the world; since introduction of its earliest versions in the 1970s, over 500 million doses have been used in over 60 countries. As with all vaccinations, long-term effects and efficacy are subject to continuing study. The vaccine is a product of Merck.
Epidemiology
Before the widespread use of a vaccine against measles, its incidence was so high that patients born before 1949 are assumed to have had measles. Today the incidence of measles has fallen to less than one percent of people under the age of 30 in countries with routine childhood vaccination. Measles has a significant complication rate, which includes pneumonitis and encephalitis.
Studies, such as a Centers for Disease Control (CDC) report on the effect of vaccination against measles in Africa between 1996-2002, have shown that vaccination markedly reduces the mortality rate due to measles.*
Mumps is another viral disease of childhood that was once very common. A known but relatively rare complication of mumps is sterility in males.
Rubella, otherwise known as German measles, was also very common before the advent of widespread vaccination. The major risk of rubella is if a pregnant woman is infected, her baby may contract congenital rubella from her, which can cause significant congenital defects.
All three diseases are highly contagious.
The MMR vaccine was introduced to induce immunity less painfully than three separate injections at the same time, sooner than at three separate encounters, and more efficiently than either. The incidence and therefore the complications of the three diseases above have declined significantly and this is generally attributed to widespread population vaccination.
Side Effects
While there are known effects, rarely serious, from each component of the MMR vaccine, from a public health perspective, the benefit to the population outweighs these concerns. Most people are in favour of continued vaccination programs.
A number of effects are reported including: a rash or slight fever for a few days, one to two weeks after receiving the vaccine, occasionally accompanied by a mild swelling of the salivary glands and some aching or swelling of the joints, respectively from the measles, mumps and rubella components, which have differing incubation periods. They are usually mild and temporary, vanishing within a few days. There are rare reports of more serious adverse effects — only about one in every 100,000 vaccinations is reported to have resulted in a severe allergic reaction.
In the UK the vaccine was once the subject of controversy, due to a 1998 paper by Dr Andrew Wakefield purporting to show a link between MMR and childhood autism. Numerous studies have since failed to show any correlation, and the vaccine is considered safe by the medical establishment.
A concerned individual may choose any one of the 3 components of the MMR vaccine separately, and it has been asserted that contrary to general medical opinion spacing out these immunizations individually may decrease the chance of adverse effects. By increasing the time until immunised, spacing the components inevitably increases opportunities for infection with at least two of the diseases for the individual and their contacts.
Development, Formulation and Administration
The component viral strains of MMR vaccine were developed by propagation in animal cells. The live viruses require animal cells as a host for production of more virus.
For example, in the case of mumps and measles viruses, the virus strains were grown in embryonated hens' eggs and chick embryo cell cultures. This produced strains of virus which were adapted for the hens egg and less well-suited for human cells. These strains are therefore called attenuated strains. They are sometimes referred to as neuroattenuated because these strains are less virulent to human neurons than the wild strains.
| Disease Immunized | Component Vaccine | Virus Strain | Propagation Medium | Growth Medium |
|---|---|---|---|---|
| Measles | Attenuvax | Enders' attenuated Edmonston strain | chick embryo cell culture | Medium 199 |
| Mumps | Mumpsvax | Jeryl Lynn (B level) strain | }}||
| Rubella | Meruvax II | Wistar RA 27/3 strain of live attenuated rubella virus | WI-38 human diploid lung fibroblasts | MEM (solution containing buffered salts, fetal bovine serum, human serum albumin and neomycin, etc.) |
The virus is extracted from the human albumin growth medium via the Cohn cold ethanol fractionation method.
MMR II is supplied freeze-dried (lyophilized) and contains live viruses. Before injection it is reconstituted with the solvent provided. It is administered by a subcutaneous injection.
Footnotes
See also
"MMR vaccine"