Madison Tavistock, a healthy 2-year-old living in Cincinnati, had attended the Wee Folks Daycare Facility for a year

Madison Tavistock, a healthy 2-year-old living in Cincinnati, had attended the Wee Folks Daycare Facility for a year. Her parents joined an anti-vaccination group when she was 9 months old, 3 months before the recommended immunization schedule for the MMR vaccine, but after Madison had already been vaccinated with DTP. They strongly believe that the unsubstantiated risk of autism reported for MMR vaccination outweighs the benefits, and consequently have opted not to have their daughter immunized. The best explanation for why Madison has not contracted measles even though she has regular contact with other children in a large city is that _____. a. Madison is tolerant to measles antigens. b. The measles virus may have infected Madison but is dormant. c. The DTP vaccine provides cross-protective immunity against measles. d. The other children in the daycare center have been vaccinated and she has herd immunity. e. The attenuated measles virus in the MMR vaccine received by the other children in her daycare facility was transmitted to Madison and she developed asymptomatic natural immunity.