Rubella is a common childhood disease, caused by rubella virus (togavirus), that may be associated with serious complications and/or death. For example, rubella during pregnancy may cause congenital rubella syndrome in the infants of infected mothers.
The impact of measles, mumps, and rubella vaccination on the natural history of each disease in the United States can be quantified by comparing the maximum number of rubella cases reported in a given year prior to vaccine use to the number of cases of each disease reported in 1995. For rubella, 57,686 cases reported in 1969 compared to 200 cases reported in 1995 resulted in a 99.65% decrease.
Extensive clinical trials of rubella virus vaccines, prepared using RA 27/3 strain rubella virus, have been carried out in more than 28,000 human subjects (approximately 11,000 with MERUVAX II) in the U.S.A. and more than 20 additional countries. A single injection of the vaccine has been shown to induce rubella hemagglutination-inhibition (HI) antibodies in 97% or more of susceptible persons. However, a small percentage (1-5%) of vaccinees may fail to seroconvert after the primary dose (see also INDICATIONS AND USAGE, Recommended Vaccination Schedule).
Efficacy of rubella vaccine was established in a series of double-blind controlled field trials which demonstrated a high degree of protective efficacy. These studies also established that seroconversion in response to rubella vaccination paralleled protection from this disease.
Following vaccination, antibodies associated with protection can be measured by neutralization assays, HI, or ELISA (enzyme linked immunosorbent assay) tests. Neutralizing and ELISA antibodies to rubella virus are still detectable in most individuals 11-13 years after primary vaccination. See INDICATIONS AND USAGE, Non-Pregnant Adolescents and Adult Females, for Rubella Susceptibility Testing.
The RA 27/3 rubella strain elicits higher immediate post-vaccination HI, complement-fixing and neutralizing antibody levels than other strains of rubella vaccine and has been shown to induce a broader profile of circulating antibodies including anti-theta and anti-iota precipitating antibodies. The RA 27/3 rubella strain immunologically simulates natural infection more closely than other rubella vaccine viruses. The increased levels and broader profile of antibodies produced by RA 27/3 strain rubella virus vaccine appear to correlate with greater resistance to subclinical reinfection with the wild virus, and provide greater confidence for lasting immunity.