Guide
Catching up on vaccines at 18 months
An 18-month-old with no prior vaccines needs about 18 doses over as few as 8 visits (18 visits at one dose per visit), against 26 doses on the on-time schedule. If Hib and PCV start right away instead of waiting for their single-dose bands, add 1 dose (19 in all). No plan finishes before 4 years, because the last DTaP and polio doses wait for the 4th birthday, 30 months after the first visit.
Key takeaways
- Of the 26 on-time doses in these 8 vaccines, 18 are still needed at 18 months: DTaP 4 instead of 5, IPV 3 instead of 4, Hib 1 instead of 4 and PCV 1 instead of 4.
- From 18 months, 3 doses per visit takes 8 visits over 2 years 6 months, ending at 4 years; one dose per visit takes 18 visits over 2 years 7 months.
- Rotavirus is no longer possible: the final dose is due before 8 months and this child is 10 months past it.
- By 18 months, an on-time child would already have had 20 of these routine doses; this plan counts none of them as given.
Doses needed at 18 months, vaccine by vaccine
| Vaccine | On time | If started now | Planner minimum | Why |
|---|---|---|---|---|
| HepB (Hepatitis B) | 3 | 3 | 3 | No reduction. Gaps of 4 weeks and 8 weeks between doses. |
| DTaP (Diphtheria, Tetanus & Pertussis) | 5 | 4–5 | 4 | 4-dose delayed path (4th dose at age ≥4 replaces doses 4 & 5). |
| IPV (Polio (Inactivated)) | 4 | 3–4 | 3 | 3-dose delayed path (3rd dose at age ≥4 is the final dose). |
| Hib (Haemophilus influenzae type b) | 4 | 1 | 1 | Start 15–59 mo: a single dose completes Hib. |
| PCV (Pneumococcal Conjugate) | 4 | 2 | 1 | Start 24–59 mo (healthy): a single dose completes PCV. |
| MMR (Measles, Mumps & Rubella) | 2 | 2 | 2 | No reduction. Second dose at least 4 weeks after the first. |
| VAR (Varicella (Chickenpox)) | 2 | 2 | 2 | No reduction. Second dose at least 3 months after the first. |
| HepA (Hepatitis A) | 2 | 2 | 2 | No reduction. The two doses are at least 6 months apart. |
"If started now" is the CDC catch-up count when the first dose is given at 18 months, as in the doses-by-start-age table. "Planner minimum" is what the planner's minimum-dose plan uses, which waits for the single-dose Hib and PCV bands.
Visits and finish age
Starting at 18 months, three doses per visit needs 10 visits fewer than one at a time and ends 1 month sooner. The required gaps set the floor: the earliest plan ends 2 years 6 months after the first visit, at 4 years.
| Pace | Visits | Doses placed | Last visit at |
|---|---|---|---|
| 1 dose per visit, 1 month apart | 18 | 18 | 4 years 1 month |
| 3 doses per visit, 1 month apart | 8 | 18 | 4 years |
| Planner preset: one vaccine per visit, 2 months apart | 18 | 18 | 4 years 4 months |
Pace figures come from the same engine as the planner, with a healthy child, the planner's default vaccines and no prior doses.
Rules that apply at 18 months
- Rotavirus (RV) is not possible: its final dose must come before 8 months, which this child passed 10 months ago.
- At 18 months the planner uses 1 dose of Hib; the CDC bands are 3 doses if the first is at 7 to 11 months; 2 doses if the first is at 12 to 14 months; 1 dose if the first is at 15 to 59 months, and none from age 5.
- At 18 months the planner uses 1 dose of PCV; the CDC bands are 3 doses if the first is at 7 to 11 months; 2 doses if the first is at 12 to 23 months; 1 dose if the first is at 24 to 59 months, and none from age 5.
- At 18 months DTaP is 4 doses and polio 3: the last dose goes at age 4 or later and at least 6 months after the one before, which is 30 months after the first visit.
- At 18 months, hepatitis A needs 6 months between its two doses, the longest fixed wait in the plan.
- 18 months is 30 months short of age 4, so the planner's note applies: Give MMR and Varicella as separate shots before age 4 (lower febrile-seizure risk).
Questions parents ask at this age
How many vaccines does an 18-month-old need to catch up?
At 18 months the plan is 18 doses (HepB 3, DTaP 4, IPV 3, Hib 1, PCV 1, MMR 2, VAR 2, HepA 2) out of 26 on the on-time series, of which an on-time child has had 20 by now.
How many visits will an 18-month-old need?
From 18 months: as few as 8 with up to 3 doses per visit (finishing at 4 years), 18 with one dose per visit and 1 month between (4 years 1 month), or 18 on the planner's one-vaccine-per-visit preset with 2 months between (4 years 4 months).
Can an 18-month-old still get the rotavirus vaccine?
No. An 18-month-old is 10 months past the rotavirus final-dose limit (no dose from 8 months), and the first dose also had to be before 15 weeks, so it is left out of this plan.
Does an 18-month-old need one or two doses of PCV?
Two if the first dose is given now (PCV's 12 to 23 month band has 2 doses, spaced 4 weeks apart), one if it waits until 24 months, which is 6 months from now. Hib is already in its single-dose band (from 15 months), so it is 1 dose either way.
Build the plan for 18 months
Enter the birth date and any doses already given; the planner counts them and spaces the rest.
Open the planner in catch-up mode One vaccine per visit Up to 4 per visitSources
Primary sources only. Links open the publisher's own page.