Measles, Mumps And Rubella Vaccination (MMR)

MEASLES, MUMPS AND RUBELLA VACCINATION (MMR)

Measles, mumps and rubella (German measles) are infectious diseases with respiratory routes of transmission and infection and each is caused by distinct members of the paramyxovirus group. Each virus only has one serotype. Although the primary multiplication sites of these viruses are within the respiratory tract, the diseases are associated with viral multiplication elsewhere in the host.

a)  Measles

Measles is a severe, acute, highly contagious infection that frequently occurs in epidemic form. After multiplication within the respiratory tract, the virus is transported throughout the body, particularly to the skin where a characteristic maculopapular rash develops. Complications of the disease can occur, including measles encephalitis, which can cause permanent neurological injury and death, and subacute, sclerosing panencephalitis (SSPE), which is a rare form of progressive encephalitis associated with persistence of the measles virus that primarily affects children and young adults. It is incurable, although early treatment can slow progression or improve the remission rate.

A live, attenuated vaccine strain of measles was introduced in the USA in 1962 and to the UK in 1968. A single injection produces high-level immunity in over 95% of recipients. Moreover, as the vaccine induces immunity more rapidly than the natural infection, it may be used to control the impact of measles outbreaks. The measles virus cannot survive outside an infected host. Widespread use of the vaccine therefore has the potential, as with smallpox, of eliminating the disease worldwide. Mass immunization has markedly reduced the incidence of measles, although a 15-fold increase in the incidence was noted in the USA between 1989 and 1991 because of poor compliance with the vaccine.

b)  Mumps

Mumps virus infects the parotid glands to cause swelling and a general viraemia. Complications include pancreatitis, meningitis and orchitis, the last occasionally leading to male sterility. Infections can also cause permanent unilateral deafness. In the absence of vaccination, infection occurs in more than 90% of individuals by age 15 years. A live, attenuated mumps vaccine has been available since 1967 and has been part of the childhood vaccination programme in the UK since 1988 when it was included as part of the MMR triple vaccine.

c)  Rubella

Rubella is a mild, often subclinical infection that is common among children aged between 4 and 9 years. Infection during the first trimester of pregnancy brings with it a major risk of abortion or congenital deformity in the fetus (congenital rubella syndrome, CRS). Rubella immunization was introduced to the UK in 1970 for pre-pubertal females and non-immune women intending to start families. The vaccine utilizes a live, cold-adapted strain of the virus. The major disadvantage of the vaccine is that, as with the wild type, the fetus can be infected. While there have been no reports of CRS associated with use of the vaccine, the possible risk makes it imperative that women do not become pregnant within 1 month of vaccination. Prepubertal females were immunized to extend the period of immunity through the childbearing years. Until 1988 boys were not routinely protected against rubella. Their susceptibility to the virus was thought to maintain the natural prevalence of the disease in the community and thereby reinforce the vaccine-induced immunity in vaccinated, adult females. This proved not to be the case and in fact cases of CRS could be related to incidence of the disease in younger children within the family. Rubella vaccine is now given to both sexes at the age of about 13 months as part of the MMR programme.

d)  MMR Vaccine

MMR vaccine was introduced to the UK in 1988 for young children of both sexes, replacing the single measles vaccine. It consists of a single dose of a lyophilized preparation of live attenuated strains of the measles, mumps and rubella viruses. The MMR vaccine had previously been deployed in the USA and Scandinavia for a significant number of years without any indication of increased adverse reaction or of decreased seroconversion over separate administration of the component parts. Immunization results in seroconversion to all three viruses in > 95% of recipients. For maximum effect, MMR vaccine is recommended for children of both sexes aged 12-15 months but can also be given to non-immune adults. From October 1996 a second dose of MMR was recommended for children aged approximately 4 years in order to prevent the re-accumulation of sufficient susceptible children to sustain future epidemics.

In 1998 a research paper attempted to associate an increase in autism to the introduction of the triple vaccine. This led to a decreased public confidence in the vaccine. Detailed examination of the data and also the results of several clinical studies have indicated that there is no association between use of the triple vaccine and autism. This is backed up by over 20 years of successful deployment of the vaccine outside of the UK. Currently, much effort is being made to restore confidence in the vaccine in order to avoid the lack of compliance leading to the occurrence of measles epidemics.