1. Overview

Polio (poliomyelitis) is a highly infectious viral disease that primarily affects young children, leading to paralysis and sometimes death. Global eradication efforts have significantly reduced cases, but challenges remain.

2. Historical Context

  • Discovery: Polio virus identified in 1908 by Karl Landsteiner and Erwin Popper.
  • Pre-Vaccine Era: Epidemics in the early 20th century caused widespread fear (e.g., 1952 US outbreak: 58,000 cases).
  • Vaccines:
    • Inactivated Polio Vaccine (IPV): Developed by Jonas Salk, 1955.
    • Oral Polio Vaccine (OPV): Developed by Albert Sabin, 1961.
  • Global Initiatives:
    • Global Polio Eradication Initiative (GPEI) launched in 1988 by WHO, Rotary International, CDC, UNICEF.

3. Biology of Polio Virus

  • Type: Enterovirus, family Picornaviridae.
  • Transmission: Fecal-oral route; contaminated water/food.
  • Symptoms: Most cases asymptomatic; ~1% develop acute flaccid paralysis.

Polio Virus Structure

4. Strategies for Eradication

4.1. Mass Vaccination

  • OPV: Easy to administer, induces gut immunity, interrupts transmission.
  • IPV: Injectable, safer (no risk of vaccine-derived polio), used in high-income countries.

4.2. Surveillance

  • Acute Flaccid Paralysis (AFP) Monitoring
  • Environmental Surveillance: Testing sewage for poliovirus.

4.3. Rapid Response

  • Outbreak containment via “mop-up” campaigns.

5. Progress and Current Status

  • Wild Polio Virus Types:
    • Type 2: Declared eradicated in 2015.
    • Type 3: Declared eradicated in 2019.
    • Type 1: Endemic in Afghanistan and Pakistan (as of 2024).
  • Cases: From 350,000 (1988) to 6 (2021) wild cases worldwide.
  • Vaccine-Derived Poliovirus (VDPV): Rare, occurs when weakened virus in OPV mutates.

6. Comparison: Polio Eradication vs. Smallpox Eradication

Aspect Polio Eradication Smallpox Eradication
Vaccine Type Live (OPV), Inactivated (IPV) Live (Vaccinia virus)
Transmission Fecal-oral Respiratory droplets
Animal Reservoirs None None
Asymptomatic Cases Common Rare
Surveillance Environmental, clinical Clinical
Eradication Status Ongoing Achieved (1980)

7. Common Misconceptions

  • Misconception 1: “Polio is no longer a threat.”
    Fact: Outbreaks can occur if vaccination coverage drops.

  • Misconception 2: “OPV is unsafe.”
    Fact: OPV is highly effective; risk of VDPV is very low compared to benefits.

  • Misconception 3: “Eradication is impossible due to asymptomatic carriers.”
    Fact: Surveillance and vaccination strategies address silent transmission.

8. Challenges

  • Conflict Zones: Inaccessibility in Afghanistan, Pakistan.
  • Vaccine Hesitancy: Misinformation, religious/cultural barriers.
  • VDPV Outbreaks: Need for high immunization coverage to prevent mutations.

9. Recent Developments

  • Novel OPV2 (nOPV2): Engineered to reduce risk of vaccine-derived outbreaks.
  • COVID-19 Impact: Disrupted immunization campaigns, increased risk of resurgence.

Citation:
Global Polio Eradication Initiative. (2022). “Novel Oral Polio Vaccine type 2 (nOPV2) rollout expands to new countries.” Link

10. Surprising Facts

  1. Polio virus can survive in sewage for weeks, making environmental surveillance critical for detection.
  2. Over 2.5 billion children have been immunized since 1988 due to global eradication efforts.
  3. Genetic sequencing of poliovirus is now used to trace outbreaks in real time, allowing for targeted vaccination campaigns.

11. Diagram: Global Polio Cases Reduction

Global Polio Cases Reduction

12. References

  • Global Polio Eradication Initiative. (2022). nOPV2 rollout expands to new countries. polioeradication.org
  • World Health Organization. (2023). Polio eradication. who.int
  • CDC. (2022). Polio elimination in the United States. cdc.gov

13. Quick Revision Points

  • Polio eradication relies on vaccination, surveillance, and rapid response.
  • Only Afghanistan and Pakistan remain endemic.
  • VDPV is a rare but manageable challenge.
  • Environmental surveillance is increasingly important.
  • Lessons from smallpox guide polio eradication strategies.

End of Revision Sheet