The timing of vaccine administration is based on age and specific intervals between doses. For example:
BCG: At birth Hepatitis B: At birth, 1 month, and 6 months DTP: At 2, 4, 6 months, with boosters at 15-18 months and 4-6 years MMR: At 12-15 months and 4-6 years Varicella: At 12-15 months and 4-6 years
