When poliovirus was detected in London in 2022, the United Kingdom of Great Britain and Northern Ireland suddenly had a real-world demonstration of why wastewater surveillance mattered. The event triggered more than an emergency response – it also helped transform wastewater surveillance in the country from a targeted scientific investigation into a routine public health tool that now plays a central role in national polio prevention efforts.
Vanessa Saliba is a consultant epidemiologist at the UK Health Security Agency (UKHSA) who oversaw the response to that detection. She explains how the wastewater surveillance system in the United Kingdom grew from a reaction to an emergency situation into a permanent nationwide system.
Caption: Vanessa Saliba. Credit: WHO.
Scaling up surveillance
For many years, just two sites in the United Kingdom had their wastewater tested for enteroviruses including poliovirus: London and Glasgow. From February 2022, concerning detections were made at the London Beckton site. In August 2022, it was formally confirmed that the United Kingdom had “circulating” vaccine-derived poliovirus type 2 (cVDPV2) based on the detection of the same isolate for more than 60 days.
Long before this confirmation, work began to identify the nexus for the detections.
“We could tell that these were related viruses, that the virus was evolving, and this was hinting that there must be some level of virus transmission in the community”, says Saliba. “But the challenge was that we were only testing this one sewage treatment works [in London] and it covers a population of close to 4 million people.”
Although no cases had been picked up at a clinical level, without action these evolving polioviruses could have paralysed unvaccinated individuals. The finding triggered a dynamic risk assessment, which established the highest-level incident response possible.
“The first thing that we wanted to do was to work out if we could sample upstream of the sewage treatment works because it was such a huge geography, which made it difficult to target the response”, says Saliba.
“We were blind”
This key step broke down surveillance from the level of a large sewage treatment works to smaller subsites, allowing teams to focus on local authority areas. That made the response more precise, but also far more complex and expensive.
“Closing streets, going down manholes to take the samples…it is a huge challenge.”
In time, this work allowed epidemiologists to home in on 8 local authority areas. Evidence provided by WHO also suggested that the virus detected in London was genetically linked to the poliovirus detected in Israel and the United States of America. This knowledge allowed UKHSA to intensify clinical surveillance in key areas and increase catch-up efforts with polio vaccine to help protect vulnerable children.
However, when the detections were first made, it was unknown if the virus was also circulating elsewhere in the country. “We were blind”, says Saliba.
With support from the London School of Hygiene and Tropical Medicine, UKHSA developed a map of the locations most likely to see importations of wild polio, or vaccine-derived polio, and which communities were least protected by vaccination. Sites linked to these locations are those still tested today, helping UKHSA to design response activities and monitor circulation.
A permanent, nationwide system
Today, UKHSA, working with the WHO Polio Global Specialized Laboratory at the Medicines and Healthcare products Regulatory Agency (MHRA), conducts routine environmental surveillance for polio in England as part of a commitment to the Global Polio Eradication Initiative. Testing is also carried out across the devolved nations. UKHSA works with water companies to collect monthly samples from 28 sites in England. London remains under more intensive surveillance, with some sites still sampled every 2 weeks. If poliovirus or a related virus is detected, testing can be increased immediately.
This system depends on close collaboration with the MHRA, which hosts the United Kingdom’s specialized polio laboratory. UKHSA and the MHRA have complementary roles: the MHRA provides laboratory expertise and sequence analysis, with additional testing capacity provided by National Health System (NHS) Lothian in Scotland, while UKHSA leads the public health response.
“Testing is one thing, but you need to know what to do when you find something and to have that relationship between the public health response and the laboratory”, says Saliba.
That collaboration is what turns laboratory data into action. Depending on the findings, UKHSA may intensify testing, alert local teams, conduct further risk assessments, or step up vaccination efforts in areas with low uptake.
The approach means that the United Kingdom is now better prepared to detect any future signals early and respond quickly. For Vanessa, the biggest lesson is that countries should not wait for an outbreak before building surveillance capacity.
“We were able to use the incident to make the case for wastewater surveillance for polio to become business as usual. There are quite a lot of outbreaks [of polio] globally so we really need to be vigilant. We do have communities who are under-vaccinated, so polio could come back. Having this surveillance system means we are more resilient and able to pick up things earlier.”
The United Kingdom’s experience shows how an outbreak can leave behind something constructive: a stronger public health system, better collaboration between laboratories and health authorities, and a model that other countries can adapt as they work to stay ahead of poliovirus.