Childhood Immunization Schedule
A Step 2 CK-focused walkthrough of the childhood immunization schedule, emphasizing which vaccines are due at each well-child visit, the live-versus-inactivated rules, and the true contraindications versus the classic 'false' reasons students wrongly defer vaccination.
Why the boards love this topic
The childhood immunization schedule is a Step 2 CK favorite tested less as rote recall and more as clinical decision-making: which vaccine is due at a given well-child visit, whether a live vaccine is safe in a specific patient, and — most commonly — recognizing that a worried parent's concern is not a true contraindication. The high-yield spine is the 2, 4, 6-month primary series (DTaP, IPV, Hib, PCV, rotavirus), the 12–15-month cluster where the first live injectables (MMR, varicella) and HepA appear, and the 11–12-year adolescent visit (Tdap, HPV, MenACWY). Master the live-vs-inactivated distinction and the short list of real contraindications, and most vignettes resolve to a confident 'vaccinate today.'
- Birth: HepB #1 (within 24 h for a medically stable infant ≥2000 g of an HBsAg-negative mother)
- 2, 4, 6 mo primary series: DTaP, IPV, Hib, PCV15/20, rotavirus (oral, live)
- Influenza: yearly starting at 6 months; first flu season under 9 yr = 2 doses ≥4 weeks apart
- 12–15 mo: MMR, varicella (first live injectables), Hib and PCV boosters, HepA (2 doses ≥6 mo apart)
- 15–18 mo: DTaP #4
- 4–6 yr: 2nd MMR, 2nd varicella, DTaP #5, IPV #4 (school-entry boosters)
- 11–12 yr: Tdap, HPV (2-dose if started before 15 yr; 3-dose if ≥15 yr or immunocompromised), MenACWY; MenACWY booster at 16 yr
- Live vaccines (MMR, varicella, rotavirus, intranasal LAIV): avoid in pregnancy and severe immunocompromise
Well-child visit at a glance
| Age | Vaccines due |
|---|---|
| Birth | HepB #1 |
| 2 mo | DTaP, IPV, Hib, PCV, rotavirus (± HepB #2) |
| 4 mo | DTaP, IPV, Hib, PCV, rotavirus |
| 6 mo | DTaP, IPV, PCV, ± Hib/rotavirus (brand-dependent), HepB #3; influenza yearly |
| 12–15 mo | MMR, varicella, Hib booster, PCV booster, HepA ×2 |
| 15–18 mo | DTaP #4 |
| 4–6 yr | DTaP #5, IPV #4, MMR #2, varicella #2 |
| 11–12 yr | Tdap, HPV, MenACWY |
| 16 yr | MenACWY booster (± MenB) |
True contraindications
- Anaphylaxis to a prior dose or vaccine component (any vaccine)
- Encephalopathy within 7 days of a pertussis-containing dose → hold the pertussis component
- Live vaccines: pregnancy, severe immunodeficiency (SCID, active chemotherapy, high-dose steroids, advanced/symptomatic HIV)
- Rotavirus: history of intussusception or SCID
NOT contraindications — vaccinate anyway (the distractors)
- Mild illness or low-grade fever, current antibiotics, prematurity (dose by chronological age)
- Breastfeeding, recent disease exposure, family history of reactions
- Egg allergy → still give age-appropriate influenza vaccine
- Pregnant or immunocompromised household contact → child may still receive MMR, varicella, and rotavirus (routine hand hygiene around the contact)
Vignette: A full-term 2-month-old presents for a well-child visit with 2 days of clear rhinorrhea and a temperature of 100.4°F (38°C). He is feeding well and playful. The mother asks whether shots should be postponed until he is 'completely better.'
Assessment: Mild, self-limited URI — a common but false reason to defer vaccination.
Next best step: Administer all due vaccines today — DTaP, IPV, Hib, PCV, and oral rotavirus. Mild acute illness with or without low-grade fever is not a contraindication; deferring only leaves the infant unprotected and risks missed follow-up. The identical logic applies to a child with egg allergy who needs the influenza vaccine — give it.
Vignette: A 12-month-old with perinatally acquired HIV is well-appearing on antiretroviral therapy; his most recent CD4 is 22%. His mother is 8 weeks pregnant. Should the MMR and varicella vaccines due today be given?
Assessment: HIV contraindicates live vaccines only when severely immunosuppressed. With age-specific CD4 ≥15% and no severe immunosuppression, MMR and varicella are indicated.
Next best step: Give MMR and varicella as two separate injections — the combined MMRV product is not recommended in HIV. The mother's pregnancy is not a barrier: household contacts of pregnant women should still receive these live vaccines. The other 12-month doses (Hib and PCV boosters, HepA) proceed on schedule — but rotavirus is not given at this visit, since its series must be completed by 8 months of age.
The 2-4-6 rule — the primary series repeats at 2, 4, and 6 months: 'DTaP, IPV, Hib, PCV, Rotavirus' — five antigens (one oral) at every well-baby visit of the first half-year.
Live vaccines 'wait for the first birthday' — MMR and varicella start at 12 months because maternal antibodies blunt the response earlier (an MMR dose given at 6–11 mo for travel doesn't count and must be repeated at ≥12 mo); HepA joins at 12 mo too.
Adolescent trio at 11–12 yr: Tdap, HPV, MenACWY — then the lone MenACWY booster at 16.
(Rotavirus is the one live vaccine that breaks the 'wait for 12 months' pattern — it's oral, must start by 15 weeks, and finish by 8 months.)
Special situations the boards recycle
- Catch-up: never restart a series — count valid prior doses and resume. An under-immunized child from abroad receives only the remaining doses at minimum intervals, not a fresh start.
- Prematurity: vaccinate by chronological (not corrected) age with full doses. The one exception is the HepB birth dose — for infants <2000 g born to HBsAg-negative mothers, delay dose 1 until 1 month of age or hospital discharge.
- HBsAg-positive mother: give HepB vaccine + HBIG within 12 hours of birth, regardless of birth weight.
- Rotavirus timing: if the series was not started by 15 weeks, do not initiate it.
Spotting these keeps the reflexive answer — vaccinate now — from becoming a trap in the rare cases where it isn't.
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