Resurgence of Wild-type poliovirus type-1

Resurgence of Wild-type poliovirus type-1


Wild-type poliovirus type-1 (WPV1) is showing signs of resurgence in Pakistan and Afghanistan since 2023, complicating the goal of eradication by 2026.

GS-02 (Health)

Key Highlights:

  • Increase in Cases: Afghanistan and Pakistan reported six WPV1 cases each in 2023, with Pakistan seeing five cases already in 2024, suggesting an upward trend that could surpass 2022 numbers.
  • Environmental Samples: Positive environmental samples of WPV1 are rising, with 153 samples from 39 districts in Pakistan by June 1, 2024, compared to 125 samples from 28 districts in 2023.
  • Historical Reservoirs: Key areas such as Karachi, Quetta, Peshawar-Khyber in Pakistan, and Kandahar in Afghanistan, are seeing increased positive environmental samples, indicating a significant risk to previous gains.
  • Polio Campaign Challenges: Ineffective polio vaccination campaigns, including fake finger marking without actual vaccination, are contributing to the resurgence.
  • Risk of International Spread: The risk of WPV1 spreading internationally, particularly from Pakistan to Afghanistan, is heightened due to the movement of over 0.5 million Afghan refugees from Pakistan, with an additional 0.8 million expected to be evicted.
  • Vulnerable Populations: The presence of unvaccinated and under-immunised children in southern Afghanistan increases the risk posed by returning refugees.

Overview of Polio

  • Highly Infectious Disease: Polio is a virus that invades the nervous system, potentially causing permanent paralysis (in 1 in 200 infections) or death (in 2-10% of paralyzed cases).
  • Transmission: The virus spreads person-to-person, mainly through the fecal-oral route or contaminated water/food.

Current Status of Wild Poliovirus

  • Eradicated Types: Two of the three types of wild poliovirus (WPV2 and WPV3) have been eradicated.
  • Endemic Countries: WPV1 is still endemic in Pakistan and Afghanistan.
  • Risk of International Spread: Detection of WPV1 outside these countries shows the ongoing risk until global eradication is achieved.

National Risk Assessment (Malawi)

  • Factors include high population density, low vaccination coverage (<80%), no recent catch-up campaign, accumulated susceptible populations, suboptimal AFP and environmental surveillance.
  • Impact of Tropical Storm Ana: The storm has affected response capacity, with significant impacts on Polio SIAs and surveillance.

Regional and Global Risk Assessment

  • Regional Risk (Moderate): Due to significant population movement between Mozambique and Malawi and suboptimal vaccination coverage and surveillance in neighboring countries.
  • Global Risk (Low): Given existing response capacity and moderately high global Polio coverage estimates.

WHO Recommendations

  • Strengthen Surveillance: Countries with frequent travel to polio-affected areas should enhance surveillance of AFP cases to detect and respond to new poliovirus importations.
  • Immediate Investigation: Under IHR (2005), countries must investigate and notify any poliovirus isolate within 24 hours of detection.
  • Routine Immunization: Maintain high routine immunization coverage (>90%) at national and subnational levels.
  • Vaccination Campaigns: Two high-quality large-scale campaigns (>90% coverage) should be completed within eight weeks of laboratory sequencing results.
  • Travel and Trade: No restrictions on travel/trade to Malawi. Travelers to polio-affected areas should be fully vaccinated.

International Health Regulations (2005)

  • PHEIC: Efforts to limit the spread of poliovirus remain a Public Health Emergency of International Concern.
  • Temporary Recommendations: Affected countries should declare outbreaks as national emergencies, consider vaccination of all international travelers, and ensure travelers have appropriate vaccination documentation.