Should we be worried about surge in poliovirus cases? Virus strains detected in European wastewaters

The number of polio cases globally has decreased by over 99% since 1988, when the World Health Organization (WHO) launched a global campaign to eradicate the paralysis-inducing disease. Despite these achievements, recent poliovirus detections in wastewater in Germany, Spain, and Poland highlight ongoing risks. While no cases of paralysis were reported in these countries, the findings serve as a wake-up call, especially as Europe has been polio-free since 2002. 

The poliovirus, which spreads via the faecal-oral route, can infect the nervous system and lead to irreversible paralysis or death.  An article by The Conversation research publication reported on the recent development in the fight against polio, recalling, that Pakistan and Afghanistan are the only endemic countries to the disease today. This  means that the disease is regularly transmitted there, yet recent outbreaks in Tajikistan and Ukraine in 2021 and Israel in 2022 are proof that polio can still spread in areas with under-immunised populations. 

Vaccination coverage plays a crucial role in determining the virus’s impact. High immunisation rates limit poliovirus to asymptomatic cases, detectable only in wastewater, whereas under-immunised populations face severe risks of outbreaks and paralysis. Current polio immunisation rates in Europe are around 95% among one-year-olds, exceeding the 80% threshold for herd immunity. However, vulnerable groups, including those with weakened immune systems, remain at risk.

Two types of polio vaccines exist: the oral polio vaccine (OPV) and the inactivated polio vaccine (IPV). The OPV, a live but weakened virus, has been instrumental in eradicating certain strains globally. However, it carries a rare risk of reverting to a dangerous form if it circulates among under-immunised populations or individuals with compromised immune systems. Conversely, the IPV cannot revert but is more expensive and logistically challenging to administer, making it less feasible in resource-poor regions.

The article notes that routine wastewater surveillance, reinvigorated during the COVID-19 pandemic, has proven invaluable for detecting disease outbreaks early. Wastewater testing in Spain, Germany, and Poland identified vaccine-derived poliovirus strains, likely shed by individuals recently vaccinated with OPV. These detections underscore the importance of maintaining high vaccination coverage to prevent the virus from regaining strength.

However, the article also warns that global challenges threaten polio eradication efforts such as armed conflicts, natural disasters, and climate change. These situations disrupt vaccination programs which leave many populations vulnerable. In 2023, 30% of countries reported vaccination rates below 80%, with some as low as 36%. The Conversation states that such gaps could lead to catastrophic consequences, reversing decades of progress.

Polio eradication has seen immense success over the past three decades due to coordinated global efforts. Yet the recent wastewater findings in Europe stress the need for sustained immunisation campaigns and robust disease surveillance. According to the article, the COVID-19 pandemic has shown that infectious diseases know no borders, reinforcing the necessity of widespread vaccination as the best defence against polio’s resurgence. Wastewater-based surveillance remains a vital tool in the fight, offering public health authorities an early warning system to protect communities from infectious diseases.

By Nazrin Sadigova