A 12-month-old girl is brought to the primary health centre for her scheduled immunisations. On review of her vaccination card, it is noted that she received BCG at birth, but the OPV doses at 6 weeks, 10 weeks, and 14 weeks were missed. Her parents are now requesting catch-up immunisation. According to the National Immunisation Schedule of India, what is the MOST appropriate next step regarding OPV administration?

Explanation

## Catch-Up Immunisation Strategy for Missed OPV Doses **Key Point:** According to the National Immunisation Schedule (NIS) of India, when all primary OPV doses are missed, the recommended catch-up approach is to **restart the OPV series from the beginning — 3 doses at 4-week intervals** — up to 5 years of age. ### NIS Catch-Up Protocol for Polio Vaccination The National Immunisation Schedule (India, 2023) and IAP guidelines specify: - **If all 3 primary OPV doses (6, 10, 14 weeks) are missed**, the series must be restarted from scratch: **3 doses of OPV at 4-week intervals**. - This applies to children up to 5 years of age. - IPV (fractional or full) is given as per the routine schedule (at 6 and 14 weeks, or as catch-up), but does **not** replace the need to complete the OPV series in a child who has received zero OPV doses. - The rationale is that OPV provides critical **mucosal (intestinal) immunity** essential for interrupting poliovirus transmission in endemic/high-risk regions like India. ### Why Restart the Full 3-Dose Series? **Clinical Pearl:** This child has received **zero OPV doses**. She is immunologically naïve to oral poliovirus vaccine. The NIS does not permit abbreviating the primary OPV series to 2 doses when all doses have been missed. The minimum number of OPV doses required for adequate mucosal immunity is 3 (primary series), and catch-up guidelines mandate restarting the full series. ### Why NOT the "2 OPV + IPV" Approach? **Warning:** The "2 OPV + IPV completion" strategy described in option D is **not a standard NIS-endorsed catch-up protocol** for a child who has missed all OPV doses. While IPV is part of the routine schedule, it does not substitute for the full OPV primary series in catch-up scenarios under the Indian NIS. ### Why NOT IPV Alone? IPV alone (option A) is not preferred in India's catch-up setting because it does not confer mucosal immunity, which is critical for poliovirus eradication in a country with ongoing transmission risk. ### Why NOT a Single OPV Dose (Option B)? A single OPV dose followed by IPV (option B) is insufficient to establish primary mucosal immunity when all 3 doses have been missed. ### Comparison of Catch-Up Strategies | Strategy | OPV Doses | NIS Recommended? | |---|---|---| | Restart full series (3 doses, 4-week intervals) | 3 | ✓ **Yes** | | 2 OPV + IPV completion | 2 | ✗ No (not for zero-dose child) | | IPV only | 0 | ✗ No | | Single OPV catch-up | 1 | ✗ No | **High-Yield:** For a child who has missed **all** primary OPV doses, the NIS mandates restarting the full 3-dose OPV series at 4-week intervals (up to age 5 years). [cite: National Immunisation Schedule, MoHFW India 2023; IAP Immunisation Timetable 2023; WHO Polio Catch-Up Guidelines]