Combination vaccines can be used for children who have fallen behind. Combination vaccines may be used when any of the components are indicated and none are contraindicated. The minimum interval between doses is the greatest interval between any of the individual antigens. For example, the minimum interval between the first and second doses of MMR is 4 weeks and the minimum interval between the first and second doses of varicella vaccine is 12 weeks. When the two vaccines are combined in MMRV (ProQuad, Merck) the minimum interval between MMRV dose #1 and dose #2 is 12 weeks, which is the greatest of the minimum intervals of the two vaccines if given separately.