Pulse Polio Immunization Program

Introduction

The Pulse Polio Immunization (PPI) program was launched in India in 1995 following the World Health Assembly resolution of 1988 for the Global Polio Eradication Initiative. It is a supplementary immunization activity (SIA) intended to complement routine immunization and achieve the goal of a polio-free world.

Scientific Rationale

The program is based on the concept of "Environmental Flooding" and the induction of high intestinal immunity:

• Mucosal Immunity: Oral Polio Vaccine (OPV) induces secretory IgA in the gut, which prevents the multiplication of wild poliovirus (WPV) and its subsequent shedding in feces.
• Environmental Flooding: Simultaneously administering OPV to all eligible children in a geographic area floods the environment with attenuated vaccine virus, displacing the WPV.
• Herd Immunity: High coverage levels ensure protection for the few individuals who may not have been vaccinated or did not seroconvert.

Implementation Strategy

The program targets all children between the ages of 0 to 5 years, regardless of their previous routine immunization status.

1. National and Sub-National Immunization Days

• National Immunization Days (NIDs): Two rounds conducted nationwide annually during the low-transmission season (usually January–March).
• Sub-National Immunization Days (SNIDs): Targeted rounds in high-risk states or districts (e.g., UP, Bihar, and urban clusters) based on surveillance data.

2. The Three-Phase Execution

• Booth Day (Day 1): Vaccination stations are set up at fixed locations (schools, booths, health centers).
• House-to-House Search (Days 2–5): Mobile teams visit every household to identify and vaccinate children who missed the booth day.
• Transit and Mobile Teams: Specialized teams vaccinate children at railway stations, bus stands, construction sites, and during transit in trains or buses.

3. Monitoring and Marking

• Finger Marking: The left little finger of the child is marked with indelible ink as a visible indicator of vaccination.
• House Marking:
  • 'P' (Protected): All eligible children in the house have been vaccinated.
  • 'X' (Missed): One or more eligible children in the house were absent or missed; these are revisited.

Acute Flaccid Paralysis (AFP) Surveillance

The diagnostic backbone of the program involves the "Gold Standard" AFP surveillance:

• Case Definition: Any child <15 years with acute onset of flaccid paralysis (including Guillain-Barré syndrome) or any person of any age where polio is suspected.
• Stool Sampling: Two "adequate" stool samples collected 24 hours apart within 14 days of onset of paralysis.
• Virological Analysis: Samples are sent under cold chain (+2 to +8°C) to WHO-accredited laboratories for viral isolation and "reverse transcription-polymerase chain reaction" (RT-PCR) to differentiate WPV from vaccine-derived poliovirus (VDPV).
• Environmental Surveillance: Routine testing of sewage samples from major urban centers to detect silent circulation of polioviruses.

The Polio Endgame Strategy and "The Switch"

As WPV Type 2 was declared eradicated in 2015, the risk shifted toward Circulating Vaccine-Derived Poliovirus Type 2 (cVDPV2).

• The Switch: On April 25, 2016, India executed a synchronized transition from Trivalent OPV (tOPV) to Bivalent OPV (bOPV, containing types 1 and 3).
• Inactivated Polio Vaccine (IPV): To maintain immunity against Type 2, fractional IPV (fIPV) was introduced into the National Immunization Schedule at 6 weeks, 14 weeks, and 9 months (intradermal).

Milestones and Current Status

• Last Case of WPV: Reported on January 13, 2011, in Howrah, West Bengal (WPV Type 1).
• Certification: India was certified "Polio Free" as part of the WHO South-East Asia Region on March 27, 2014.
• Current Vigilance: Maintaining high population immunity is critical to prevent the importation of WPV from remaining endemic countries (Pakistan and Afghanistan).