How can we quickly determine how to “catch up” children who have fallen behind on their shots?

As a general rule, infants or children who are more than 1 month or 1 dose behind schedule should be on an accelerated schedule, which means the intervals between doses should be reduced to the minimum allowable. Catch-up schedules for children ages 4 months through 18 years are included in Table 2 of each year’s recommended immunization schedule for children and adolescents published by CDC. To review Table 2, go to www.cdc.gov/vaccines/hcp/imz-schedules/child-adolescent-age.html and open the current schedule for children and adolescents.

The recommended immunization schedule published by the American Academy of Pediatrics (AAP) also includes a catch-up schedule as Table 2 of its schedule, available here: https://downloads.aap.org/AAP/PDF/AAP-Immunization-Schedule.pdf.