Polio Resurgence

The World Health Organization (WHO) has reported a resurgence of polio globally, with cases and environmental samples of polio virus detected in several countries.

Global Spread of Polio:

• Wild poliovirus cases have decreased by over 99% since 1988, from an estimated 350 000 cases in more than 125 endemic countries to 12 reported cases in 2023.
• Of the 3 strains of wild poliovirus (type 1, type 2 and type 3), wild poliovirus type 2 was eradicated in 1999 and wild poliovirus type 3 was eradicated in 2020.
• As of 2024, endemic wild poliovirus type 1 remains in two countries: Pakistan and Afghanistan.
• However, the virus has been found in wastewater samples from countries like Finland, Germany, Poland, Spain, and the UK. While no confirmed human cases have been reported in these countries, the detection of the virus highlights the ongoing risk of polio despite high vaccination coverage.
• In addition to European countries, cases of wild poliovirus (WPV) and vaccine-derived poliovirus (cVDPV) have been detected in countries like Pakistan, Cameroon, Cote d'Ivoire, Chad, and Nigeria.
• The virus has been found in sewage samples in cities such as Barcelona (Spain), Warsaw (Poland), and several cities in Germany and the UK.
• Notably, these viruses are genetically linked to strains from countries like Nigeria.
• Ongoing Surveillance and Vaccination: WHO continues to emphasize the importance of surveillance and vaccination.
  • Despite high vaccination coverage (85-95% of children receiving polio vaccines), there are pockets of undervaccination in certain areas, leaving gaps in immunity that can allow the virus to spread.
  • These gaps must be addressed through targeted vaccination campaigns and continuous monitoring of immunity levels.

The Debate Over Polio Vaccines:

• Role of Oral Polio Vaccine (OPV): The oral polio vaccine (OPV) has been a key tool in the global effort to eradicate polio.
  • It is a live-attenuated vaccine, meaning it uses a weakened form of the virus to stimulate immunity.
  • OPV has been effective in large-scale immunization campaigns, especially in low-resource settings.
  • However, OPV has a downside: in rare cases, it can lead to vaccine-derived polio (cVDPV), where the weakened virus in the vaccine mutates and causes new polio outbreaks.
• Shift in Transmission Theory: For years, polio was thought to primarily spread through the faecal-oral route—when contaminated feces from an infected person are ingested, often through dirty water or food.
  • This led to the widespread use of OPV. However, recent research suggests that respiratory transmission—through coughing or sneezing—may play a larger role in spreading the virus than previously thought.
  • This theory challenges the long-held belief in the faecal-oral route as the dominant mode of transmission.
• Case for Injected Polio Vaccine (IPV): A recent report argues that respiratory transmission might be the main way polio spreads, particularly for wild poliovirus (WPV) and vaccine-derived poliovirus (cVDPV).
  • They suggest that injectable polio vaccine (IPV), which is non-transmissible (unlike OPV), should be used exclusively for polio eradication.
  • IPV is injected rather than taken orally, and does not carry the risk of vaccine-derived polio. The OPV-to-IPV switch should be accelerated globally to effectively eradicate polio.