The new nurse asks the experienced nurse why the first dose of the MMR vaccine is normally given at 12 to 15 months of age and not earlier, except with international travel. Which explanation by the experienced nurse is correct?

A: The second dose of the MMR vaccine can be given earlier, provided that at least 4 weeks has elapsed since the first dose. However, a second dose is usually not given earlier because sufficient immunity is usually present. B: The chance of developing only measles is greater if the vaccine is given at a younger age because the vaccine may neutralize the passive antibodies. C: The MMR provides active (not passive) immunity. D: Because the MMR vaccine is a live virus, a person develops a mild form of the diseases after administration, stimulating the body to develop immunity. The passively acquired antibodies to measles can interfere with the child's immune response to the vaccine, and no immunity may result.