Yesterday, declaring a “national incident” after poliovirus was detected in London’s sewage, UK public health officials asked doctors to be on alert for polio cases and urged residents to check whether are up to date with their rare disease vaccinations. The source of the virus is still a mystery, but it was likely someone outside the UK who had recently received the oral polio vaccine (OPV), which uses a live, but weakened virus, and is no longer given in the UK.
Most polio infections are asymptomatic and no cases have been found in the UK so far. But with vaccination rates below 90% in some London communities, there is concern it won’t last. The emergence of the poliovirus in London is a reminder “that no country is immune from being reinfected by polio or re-emerging until the disease has been eradicated everywhere,” says Oliver Rosenbauer, spokesperson for the World Organization’s Global Polio Eradication Initiative. health care.
Polio has been eliminated in much of the world, but the virus is still endemic in Afghanistan and Pakistan, and 30 other countries in Africa, Europe and the Middle East are now designated “hotbed countries”, where the virus has recently circulated. The spread is seeded by the wild virus that persists in Afghanistan or Pakistan or the OPV virus which has regained the ability to cause disease in unvaccinated people.
In the UK, the virus was detected in samples taken between February and June by the Beckton Sewage Treatment Works, which processes the wastewater of 4 million people in North and East London. Initially it did not raise the alarm; UK wastewater monitoring programs usually detect some of these samples each year, spilled by recent arrivals who have received OPVs.
Such traces of sewage usually disappear again quite quickly. This time around, the virus continued to appear in London for several months, and several closely related versions of the virus have emerged in the latest samples. Genetic changes suggest that the virus is continuing to evolve, a sign that it could spread to a small number of people.
Joseph Swan, a polio communications officer at WHO, says wider spread is unlikely given the generally high vaccination coverage in the UK, which like most wealthy countries uses multiple doses of a vaccine against it. virus killed. And he points out that there is still no direct evidence that the virus is spreading from person to person. But officials are encouraging people to verify that they and their children have received all recommended doses of the vaccine.
London’s polio detection is the second this year in a place that doesn’t usually have the virus. On March 7, an unvaccinated 3-year-old boy in Israel who had developed paralysis was diagnosed with polio and the country has detected poliovirus in 25 sewage samples so far this year, mostly in or near Jerusalem. The virus is also a vaccine-derived strain, but it is the type 3 strain, unrelated to the type 2 virus found in London. Rapid detection in both Israel and the UK shows polio surveillance systems are working, Rosenbauer says.
In response, Israel and the Palestinian National Authority have stepped up vaccination efforts and the virus has not been detected in the sewage there since March. But COVID-19 has made the job more difficult, says Itamar Grotto, an infectious disease epidemiologist at Ben-Gurion University of the Negev. Both public health and public health personnel are frayed after the pandemic and multiple COVID-19 vaccination campaigns, he says, and vaccine hesitation has increased in some groups.
Officials in London are now taking samples in the sewer systems upstream of Beckton’s treatment plant, to see if they can narrow down the source of the virus and perhaps target vaccination campaigns more precisely.
The OPV that brought the virus to both the UK and Israel has advantages in regions where the poliovirus is spreading. Not only is it cheap and easy to administer, but even the live virus in the vaccine can still replicate in a recipient, triggering strong immune protection in the gut that can stop further transmission of the virus, helping to strengthen the community’s defenses against future. outbreaks. And while it occasionally evolves to regain its virulence, health officials are starting to roll out a more stable form of OPV which they hope will reduce the risk of these reversions.
Meanwhile, Rosenbauer says: “The main thing that countries can do … is to ensure strong disease surveillance and high vaccination coverage, to minimize the risk and consequences of reappearance.”