Clinical studies of 237 double seronegative children, 10 months to 10 years of age, demonstrated that M-R-VAX II is highly immunogenic and generally well tolerated. In these studies, a single injection of the vaccine induced measles hemagglutination-inhibition (HI) antibodies in 95 percent and rubella HI antibodies in 99 percent of susceptible persons.

The RA 27/3 rubella strain in M-R-VAX II 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.

Vaccine induced antibody levels following administration of M-R-VAX II have been shown to persist up to 11 years without substantial decline. Continued surveillance will be necessary to determine further duration of antibody persistence.

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