A vaccine-derived version of poliovirus has repeatedly surfaced in London sewage over the past several months, suggesting there may be a cryptic or hidden spread among some unvaccinated people, UK health officials announced Wednesday.
No polio cases have been reported so far, nor any identified cases of paralysis. But sewage sampling in one London treatment plant has repeatedly detected closely related vaccine-derived polioviruses between February and May.
This suggests “it is likely there has been some spread between closely-linked individuals in North and East London and that they are now shedding the type 2 poliovirus strain in their feces,” the UK Health Security Agency (UKHSA) said
Though the current situation raises alarm, the agency notes that it’s otherwise common to see a small number of vaccine-like polioviruses pop up in sewage from time to time, usually from people who have recently been vaccinated out of the country.
This is because many countries use oral polio vaccines that include weakened (attenuated) polioviruses, which can still replicate in the intestines and thus be present in stool. They can also spread to others via poor hygiene and sanitation.
Most people infected with poliovirus have no symptoms, but about a quarter will develop a flu-like illness that clears on its own, according to the Centers for Disease Control and Prevention. In a smaller proportion—estimated to be between 1- to 5-in-1,000—the virus attacks the central nervous system, leading to more severe symptoms, including tingling in legs and arms, meningitis, and paralysis.
The CDC estimates that about 1-in-200 people infected with poliovirus will develop paralysis. And about 2 percent to 10 percent of people with paralytic polio will die because the paralysis will affect their ability to breathe.