MMR vaccine

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 sold by e.g. Merck as M-M-R II, GlaxoSmithKline Biologicals as Priorix, and sanofi pasteur as TRIMOVAX. 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. It also increases the likelihood of immunization against rubella in populations for which it has no meaningful use (all those other than pregnant women) given the costs, inconvenience and possible side-effects of vaccination, including arthritis and encephalitis. The incidence and therefore the complications of the three diseases above have declined significantly and this is generally attributed to widespread population vaccination.

Adverse Effects
There are a number of adverse effects listed in the product documentation for the MMR vaccine. Additional side effects and variants 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 &mdash; only about one in every 100,000 vaccinations is reported to have resulted in a severe adverse effect such as encephalitis or meningitis. Acute disseminated encephalomyelitis is a rare severe adverse effect of the vaccine.

The medical community does recognize that effects, rarely serious, may occur from each component of the MMR vaccine. However, the consensus of medical opinion is that the vaccine is very safe. In the opinion of most public health authorities, the benefit to the population outweighs these concerns.

Parents may choose to have each of the three components given separately, but the overwhelming medical opinion is that such spacing of injections does not reduce the chance of adverse effects, but increases the opportunity for infection by the two diseases not immunized against first.

Retracted report associating vaccine with autism
In the UK, the vaccine was the subject of controversy after a 1998 paper by Dr. Andrew Wakefield, which Wakefield claimed had found a possible link between MMR and the onset of autism and bowel disease in children. Numerous peer-reviewed studies have since failed to show any correlation. Since its publication, this conclusion of the study has been retracted by ten of Wakefield's twelve co-authors, and his call for parents to boycott the vaccine in favor of single injections one year apart, has been heavily criticized, both on scientific grounds and for triggering a decline in vaccination rates.

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.

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.