Which vaccines require a minimum age of 12 months before administration?

The answer identifying MMR (Measles, Mumps, Rubella), Varicella (Chickenpox), and Hepatitis A as requiring a minimum age of 12 months for administration is correct because these vaccines are specifically designed to be given during the early childhood vaccination schedule, which begins at this age.

Vaccines like MMR and Varicella are live attenuated vaccines, and the immune system of an infant younger than 12 months may not respond adequately to these types of vaccines, reducing their efficacy. Therefore, the recommendation is to wait until the child is at least one year old, which allows for a stronger immune response to these vaccinations, thus ensuring better protection against these diseases. Hepatitis A is also recommended starting at 12 months of age for similar reasons regarding immune development.

Other vaccines listed in the incorrect choices may have different minimum age requirements or are given at earlier stages, reflecting different considerations based on the nature of the vaccines, the age of the child, and the immune response needed to effectively fight off potential infections.