# Catch-up Immunisation > Catch-up immunisation for NEET-PG Paediatrics: never restart rule, minimum intervals, preterm and unknown-record rules and IAP guidance notes. - Canonical URL: https://prepelephant.com/topics/neet-pg/paediatrics/catch-up-immunisation - Exam / course: NEET-PG · Subject: Paediatrics - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Catch-up Immunisation", PrepElephant, https://prepelephant.com/topics/neet-pg/paediatrics/catch-up-immunisation ## Direct answer An interrupted vaccine series is never restarted: however long the gap, doses already given count and the schedule simply resumes — the most tested principle of catch-up immunisation under IAP guidance. Catch-up is governed by minimum ages (a dose given too early does not count) and minimum intervals: DTP needs four weeks between the first three doses and six months before the booster (at twelve months or older); hepatitis B needs four-week gaps with the final dose at 24 weeks or later; MMR needs four weeks between doses; and live vaccines given on different days need four weeks apart. Preterm babies are vaccinated at chronological age, a child with unknown records is assumed unimmunised, and serology is rarely needed. ## What you must remember - **Never restart:** every valid dose counts forever; excessive intervals add nothing but delay — resume the series as if the gap never happened. - **Minimum interval grid:** DTP doses 1-2 and 2-3 at least 4 weeks apart, dose 3-4 at least 6 months with dose 4 at 12 months or later; hepatitis B with four-week gaps and the last dose beyond 24 weeks of age; MMR two doses at least 4 weeks apart. - **Age ceilings:** rotavirus should not be initiated beyond about 15 weeks or completed beyond 8 months; other vaccines have no upper limits for catch-up. - **Too early does not count:** any dose given before the minimum age or interval is repeated after the required interval. - **Preterm rule:** immunise at chronological age from birth; babies under 2 kg of hepatitis-B-surface-antigen-negative mothers have the birth dose counted from one month or discharge, while those of positive mothers receive vaccine plus immunoglobulin within 12 hours. - **Live vaccine spacing:** two live vaccines on the same day or at least 4 weeks apart; BCG beyond the neonatal period follows national guidance. - **Unknown records:** an undocumented child is treated as unimmunised and given an age-appropriate series — assume nothing, restart everything, without serology for routine antigens. ## Working through an unimmunised two-year-old A two-year-old relocating from a rural district arrives with no immunisation card and a mother who recalls "some injections". The steps: assume no valid doses, and construct an age-appropriate catch-up. Day one gives BCG (after tuberculin consideration per current guidance), the first DTwP/DTaP, the first polio dose, the first hepatitis B, the first Hib, pneumococcal conjugate, and the first MMR; rotavirus is beyond its age ceiling and omitted. Four weeks later, the second doses of DTP, polio, hepatitis B, Hib and pneumococcus fall due; the second MMR can follow four weeks after the first. The DTP booster logic completes the grid — the fourth dose at least six months after the third and at 12 months or older, with further boosters per the IAP schedule, and typhoid conjugate and hepatitis A offered from one year of age. Compare the child with two documented DTP doses and a two-year gap: nothing restarts; the third dose is simply given now, and the schedule proceeds with its minimum intervals — the contrast between the two children is the entire teaching point. ## Where students slip The restart reflex is the scripted error: decades of "course must be completed" teaching makes candidates restart interrupted series, whereas both IAP and international guidance count every valid dose regardless of delay. The second slip is the minimum-versus-recommended confusion — the recommended interval is what the schedule shows, the minimum interval is what catch-up uses, and only doses violating the minimum are repeated. The third is the live-vaccine spacing rule and the rotavirus ceiling, both of which convert into single-best-answer traps. The Indian viva layering expects programme fluency: the IAP catch-up tables and the practical instruction that an undocumented child is restarted age-appropriately — the examiner wants the doctor who can rebuild a schedule at the clinic table, not recite one. ## Frequently asked questions ### Should an interrupted vaccine series be restarted? No — all previously administered valid doses count regardless of the interval elapsed, and the series resumes where it stopped. ### What are the minimum intervals for DTP and hepatitis B catch-up? At least four weeks between DTP doses 1-2 and 2-3 with six months before the booster (given at 12 months or older); hepatitis B doses at least four weeks apart with the final dose at 24 weeks of age or later. ### When are two live vaccines given? Either on the same day or separated by at least four weeks; shorter gaps risk interference from the first virus blocking the second. ### How is a preterm baby immunised? At chronological age from birth, using full doses, with the hepatitis B birth dose in infants under 2 kg deferred to one month or discharge when the mother is hepatitis-B-surface-antigen negative. ### What is done for a child with no immunisation records? Treat as unimmunised and begin an age-appropriate catch-up series without routine serology, applying minimum ages and intervals rather than restarting later doses.