The MMR vaccine contains at least 1000 median tissue culture infective doses (TCID₅₀) of the measles Moraten strain, at least 5000 TCID₅₀ of the mumps Jeryl Lynn strain, and at least 1000 TCID₅₀ of the RA27/3 strain. This combination regimen has been shown to be as effective in combating all the replication of all three viruses as they would be in their monovalent forms.(7)

Merck produces this MMR vaccine. Several other manufacturers produce MMR vaccines that include different measles and mumps strains. The RA27/3 strain is common to all.(9)

Given in one injection, this formulation is actually a combination of the vaccines for each disease. Thus, the MMR vaccine can be categorized as a combination vaccine. It is composed of three separate immunogens that have been physically connected and are administered in one inoculation. Due to the increasing number of available vaccines, many of these are now being combined in a single preparation.(11) Combination vaccines minimize the amount of economic and logistical nuisance involved in immunization both for the patient and the provider. Moreover, the efficacy of these vaccines is not reduced when combined into a regimen compared to individual administration.(26)

Ideal combination vaccines should be similar in their physical, chemical, and biologic properties. The efficacy of each vaccine should be mutually exclusive; they should not interfere with each other in generating an immune response. If too many vaccines are combined into one regimen, then there is a potential risk for antigenic competition and interference.(2) Peptides from different protein antigens may compete for sites on an MHC receptor or the MHC-peptide complex may be differentially recognized by T-cell receptors. Fortunately, antigenic competition is minimized with the strains constituting the MMR vaccine. Additionally, the individual strains of MMR are all aimed at generating an neutralizing IgG and cell-mediated response. For this reason, the strains share a common site of administration and can all be injected subcutaneously.(7)

The MMR vaccine contains attenuated doses of the measles Moraten strain, the mumps Jeryl Lynn strain, and the rubella RA27/3 strain. Since these three candidates are all live strain, they were all combined under one vaccine. Meanwhile, other combination vaccines such as the Diphtheria-tetanus toxoid pertussis vaccine (DTP) and the DTPa, Haemophilus influenzae b, and hepatitis B vaccine all consist of inactivated candidates.(2) Thus, we see that the ìlivenessî of strains must also be similar in a combination vaccine.