Which feature best distinguishes Oral Polio Vaccine (OPV) from Inactivated Polio Vaccine (IPV) in the context of India's Universal Immunisation Programme?

Explanation

## Distinguishing OPV from IPV ### Mucosal vs Systemic Immunity **Key Point:** The most critical discriminator between OPV and IPV is the type of immune response generated. - **OPV (Oral Polio Vaccine)** - Live attenuated vaccine administered orally - Induces **mucosal (IgA) immunity** in the gut - Also generates systemic (IgG) immunity - Provides herd immunity due to vaccine virus shedding - **IPV (Inactivated Polio Vaccine)** - Inactivated (killed) vaccine administered intramuscularly - Induces primarily **systemic (IgG) immunity** - Does NOT generate mucosal immunity - No herd immunity; requires individual vaccination ### Clinical Significance in India's UIP **High-Yield:** India transitioned from OPV-only to a mixed schedule (IPV + OPV) and then to IPV-only in 2014 as part of polio eradication strategy. The mucosal immunity from OPV was critical for breaking wild poliovirus transmission in endemic regions. ### Why Mucosal Immunity Matters **Clinical Pearl:** Mucosal IgA prevents poliovirus replication at the site of entry (intestinal epithelium), blocking both infection AND shedding of vaccine virus. This is why OPV was superior for outbreak control in high-transmission settings. ### Comparison Table | Feature | OPV | IPV | |---------|-----|-----| | **Type** | Live attenuated | Inactivated | | **Route** | Oral | Intramuscular | | **Mucosal immunity** | Yes (IgA) | No | | **Systemic immunity** | Yes (IgG) | Yes (IgG) | | **Herd immunity** | Yes (vaccine shedding) | No | | **Adverse effects** | VAPP (1 in 2.4–3 million) | None (inactivated) | | **Heat stability** | Moderate | Requires cold chain | [cite:Park 26e Ch 8]