Polio Eradication

On this page

Polio: The Virus - Viral Villainy

Poliovirus structure, cell entry, and genome

  • Virus: Picornavirus family (Enterovirus C species), non-enveloped, single-stranded RNA (ssRNA). Highly infectious.
  • Serotypes (3): Based on capsid proteins (VP1, VP2, VP3).
    • WPV1 (Wild Poliovirus Type 1): Only wild type currently circulating; responsible for all recent WPV outbreaks.
    • WPV2 (Wild Poliovirus Type 2): Declared globally eradicated (September 2015).
    • WPV3 (Wild Poliovirus Type 3): Declared globally eradicated (October 2019).
  • Transmission: Primarily fecal-oral route. Oral-oral (respiratory secretions) possible, especially early in infection.
  • Incubation Period: Commonly 7-14 days (range 3-35 days).
  • Pathogenesis: Enters via mouth → replicates in oropharynx & GIT (Peyer’s patches) → viremia → invades CNS (preferentially anterior horn cells of spinal cord, motor nuclei of brainstem) → motor neuron destruction → flaccid paralysis.
  • Clinical Spectrum:
    • 90% Asymptomatic infections.

    • ~4-8% Minor, non-specific illness (abortive poliomyelitis; fever, malaise, sore throat).
    • ~1-2% Non-paralytic aseptic meningitis (stiffness of neck/back/legs).
    • <1% Paralytic poliomyelitis (hallmark: asymmetric Acute Flaccid Paralysis - AFP, no sensory loss).
  • Reservoir: Humans only (no animal reservoir).
  • Period of Communicability: Virus shed in throat secretions for ~1 week (starting 36-48 hrs after infection) and in feces for 3-6 weeks or longer (starting 72 hrs after infection). Max communicability shortly before and after clinical onset.

⭐ Wild Poliovirus type 2 (WPV2) was declared globally eradicated in September 2015, and WPV3 in October 2019. Only WPV1 continues to circulate in endemic areas or cause outbreaks through importation. This makes WPV1 the sole target for wild polio eradication efforts now focusing on the last endemic countries (Pakistan and Afghanistan).

Polio Vaccines - Shielding Strategies

  • Oral Polio Vaccine (OPV) - Sabin

    • Live attenuated (tOPV, bOPV, mOPV).
    • Oral, 2 drops.
    • Immunity: Humoral (IgG) & strong mucosal (IgA) → gut immunity, ↓ transmission.
    • Risk: VAPP (1/2.7M doses), VDPV.
    • 📌 Mnemonic: "SABIN = Stomach And Bowel Immunity Now".
  • Inactivated Polio Vaccine (IPV) - Salk

    • Killed virus.
    • Route: IM (0.5mL) or fIPV-ID (0.1mL).
    • Immunity: Humoral (IgG) only; poor gut immunity.
    • Advantage: No VAPP/VDPV. Safe for immunocompromised.
  • OPV vs IPV Comparison

    FeatureOPV (Sabin)IPV (Salk)
    TypeLive attenuatedKilled
    RouteOral (2 drops)Injection (IM/ID)
    ImmunityIgG, Strong IgA (gut)IgG only (poor gut)
    VAPP/VDPVYesNo
    CostLowHigh
    Secondary SpreadYesNo

⭐ India switched tOPV to bOPV: April 25, 2016 (Polio Endgame Strategy).

Eradication: Global & India - The Long Fight

  • Global Polio Eradication Initiative (GPEI): Launched 1988.
    • Partners: WHO, UNICEF, Rotary, CDC, BMGF, Gavi.
    • Core Strategies: Routine immunization, SIAs (NIDs, SNIDs), AFP surveillance (≥2/100,000 <15 yrs), mop-up.
    • Status: WPV2 eradicated (2015), WPV3 eradicated (2019). WPV1 endemic: Afghanistan, Pakistan. cVDPV outbreaks persist.
  • India's Eradication Journey:
    • Pulse Polio Immunization (PPI) since 1995.
    • Last WPV1 case: 13 Jan 2011 (Howrah, WB).
    • Key to success: High PPI coverage, robust surveillance, IPV introduction (2015), tOPV to bOPV switch (April 2016).

⭐ WHO certified India polio-free on 27 March 2014, along with the entire South-East Asia Region.

Global Polio Eradication Progress 2023

Polio Endgame - Securing Victory

  • Polio Endgame Strategic Plan (2019-2023): Achieve & sustain polio-free world. Objectives:

    • Interrupt all poliovirus transmission (WPV & cVDPV).
    • Strengthen immunization; complete OPV withdrawal.
    • Contain poliovirus stocks (GAPIII).
    • Transition polio assets (legacy).
  • Key Transition: OPV Switch & IPV Introduction

  • Containment: GAPIII (Global Action Plan III)

    • Minimize facility-associated poliovirus risk post-eradication.
    • Safe handling/storage of poliovirus materials.
  • Maintaining Polio-Free Status:

    • High population immunity (bOPV + IPV).
    • Vigilant AFP & environmental surveillance.
    • Rapid outbreak response (mOPV2 for cVDPV2).

    ⭐ India was certified Polio-free by WHO on 27 March 2014. Last WPV case: 13 Jan 2011.

High‑Yield Points - ⚡ Biggest Takeaways

  • India declared polio-free by WHO on March 27, 2014.
  • Last wild poliovirus case in India: January 13, 2011, West Bengal (WPV1).
  • OPV (Sabin): Live attenuated, provides mucosal & humoral immunity, carries VAPP risk.
  • IPV (Salk): Killed, provides humoral immunity only, part of Polio Endgame Strategy.
  • bOPV (P1 & P3) replaced tOPV in April 2016 after WPV2 eradication.
  • AFP surveillance target: Non-polio AFP rate ≥2 per 100,000 children <15 years.

Practice Questions: Polio Eradication

Test your understanding with these related questions

Which of the following is NOT a core component of the WHO's global STI control strategy?

1 of 5

Flashcards: Polio Eradication

1/10

Which strains of poliovirus have been eradicated worldwide?_____

TAP TO REVEAL ANSWER

Which strains of poliovirus have been eradicated worldwide?_____

Type II and III

browseSpaceflip

Enjoying this lesson?

Get full access to all lessons, practice questions, and more.

Start Your Free Trial