A first dose of this vaccine should be given at 12-13 months of age and a second dose before starting school at 3 years and 4 months to 5 years of age.

• A. Diphtheria
• B. MMR
• C. Rotavirus
• D. Vitamin D

Answer: (B)

Two-dose MMR timing is designed to maximize protection against measles, mumps and rubella. The first dose is given at about 12–13 months because by then maternal antibodies wane enough for the vaccine to provoke a reliable immune response, establishing initial immunity. A second dose is scheduled before starting school, around 3 years 4 months to 5 years, to boost immunity and catch any individuals who did not respond fully to the first dose, ensuring immunity in the broad population. Together, this two-dose schedule raises overall effectiveness to well over 95%.

Rotavirus vaccines are given in infancy (typically 2, 4, and sometimes 6 months) and must be completed by around 6 months, so they wouldn’t be administered at 12–13 months. Diphtheria-containing vaccines start in infancy and include boosters later, not matching the described pre-school timing. Vitamin D isn’t a vaccine at all, but a supplement.