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Polio’s Arrival in the London Sewer System Is Worrying Experts

Polio’s Arrival in the London Sewer System Is Worrying Experts

The U.K.’s most recent case of polio occurred in 1984, and the disease was declared formally eradicated there in 2004. But the country is on edge this week after the poliovirus was discovered in several sewage samples in London, giving rise to what government health officials call a “national incident.” No new cases of polio have been confirmed in the U.K. But according to an alert by the U.K. Health Security Agency, “it is likely there has been some spread between closely linked individuals in north and east London and they are shedding the type 2 poliovirus strain in their feces.” (There were originally three strains of poliovirus, but types 1 and 3 have been vaccinated out of existence.)

The virus that was detected in London wastewater is not the so-called “wild” poliovirus, which used to circulate freely around the world but has now been eradicated in all but two countries: Afghanistan and Pakistan. Rather, it is what is known as “vaccine-derived” poliovirus. There are two types of polio vaccines: the injectable version, which uses a killed virus to confer immunity, and the oral version, which uses a live but weakened virus. The oral version is easier and cheaper to administer and is thus the vaccine of choice for mass immunizations. But on occasion, the harmless, weakened virus can mutate to the infectious, paralytic form, pass through the body in feces, and threaten to infect individuals. That is what experts fear could happen in London.

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Officials have no way of knowing who the original source of the virus is, but it was likely a visitor from another country, since the U.K. switched from the oral…

Read full article on time.com