Missed a dose: do you restart the series?

What do the CDC rules say about a late dose?

The CDC's general best practice guidance says that an interruption in the schedule does not require restarting the entire series. It also says intervals longer than recommended typically do not reduce final antibody concentrations. The catch-up schedule is built the same way: see the catch-up guide for how remaining doses are counted.

What are minimum ages and minimum intervals?

A minimum age is the youngest age at which a dose counts. A minimum interval is the shortest wait after the previous dose. They are floors, not deadlines: you can give a dose later, but not sooner. For example, the CDC catch-up schedule lists MMR as 2 doses, the second at least 4 weeks after the first.

• A dose given 5 or more days earlier than the minimum age or interval is not counted as valid and is repeated.
• A dose given 4 days or fewer before the minimum is considered valid (the 4-day grace period). The CDC notes that local or state mandates might supersede it.
• A repeat dose is spaced after the invalid dose by the recommended minimum interval.

Which situations are different?

Rotavirus is the main one. The CDC says rotavirus vaccination should not be started for infants aged 15 weeks, 0 days or older, and doses must be finished by age 8 months, 0 days. A missed rotavirus dose may simply be too late to give; see rotavirus details. Some vaccines also need fewer doses when a healthy child starts later (Hib, PCV, DTaP and polio), so the number of remaining doses depends on the child's current age, not only on what was missed.

What should you do next?

1. Find your child's record with the date of every dose. If it is lost, see how to find vaccine records.
2. Note which doses are valid (right age, right interval).
3. Check the school deadline for your state on the requirements by state pages.
4. Ask your practitioner for the next dose, or build a plan in the planner and bring it to the visit.

Common questions

We missed a dose by a few months. Do we start the series over?

No. The CDC says an interruption in the schedule does not require restarting the entire series. Count the doses already given and give the next one as soon as it is practical, at or after its minimum interval. Ask your child's practitioner to confirm which dose is next.

Does waiting longer between doses weaken protection?

The CDC says intervals longer than recommended typically do not reduce final antibody concentrations. The cost of a gap is time: your child is not fully protected until the last dose is given, so the CDC advises giving doses as close to the recommended intervals as possible.

What if a dose was given too early?

A dose given 5 or more days before the minimum age or interval is not counted as valid and is repeated. A dose given up to 4 days early is considered valid. The repeat is spaced from the invalid dose by the minimum interval. For example, a first varicella dose given at 10 months is repeated no earlier than the first birthday.

Is there any vaccine where a gap means starting again?

The CDC names one exception to the no-restart rule: oral typhoid vaccine, which is not a routine childhood vaccine. The CDC page does not list any routine childhood vaccine that has to be restarted. Rotavirus is a different problem: it cannot be caught up once the child is past its age limits (see below). For anything else, ask your practitioner.

Can I use the planner if we are behind?

Yes. Enter the doses already given under "Already had some shots?" and the planner schedules only what is left, with every dose placed at or after its minimum age and interval. It is for healthy children; see who should not use this tool.