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. Two types of polio vaccines are available: an injectable one that uses a dead virus to instill immunity and an oral one which uses a weakened but still active virus. Because it is simpler and more affordable to administer, the oral vaccine is preferred for mass vaccinations. The virus, which is usually harmless and weak, can sometimes become infectious. It may also pass through the body via feces and potentially infect others. Experts fear that this could occur in London.

Officials don’t know the source of this virus, but they believe it to be a foreign visitor. The injectable vaccine was switched to the U.K. in 2004 to stop the spread of such contaminated vaccines. While 86.6% of British children have been vaccinated via injection and are therefore protected, that still leaves more than 13% who are vulnerable to the newly discovered virus, and officials are urging those children (and anyone who isn’t inoculated against polio) to get vaccinated.

“Vaccine-derived poliovirus has the potential to spread, particularly in communities where vaccine uptake is lower,” said Dr. Vabessa Saliba, an epidemiologist at the U.K. Health Security Agency, in a statement.

Although the presence of the virus is concerning in London, it does not necessarily indicate a health crisis. Though vaccine-derived paralysis can sometimes cause paralysis when it circulates, this is a rare occurrence. Others experience only mild symptoms like a cold or never develop any symptoms.

Public health officials are now trying to find the source of the contaminated wastewater through the first location it was identified. Problem is, the plant processes waste from millions of people. It makes it difficult for anyone to pinpoint the exact source. However, the World Health Organization reported that samples of sewage flowing upstream from the facility are being taken to identify the areas where contamination took place.

At this time, it does not seem that the virus has spread to the rest of the country. If any infections do turn up, health officials would be able to type the strain of the virus and determine if it’s the same as the one that was isolated in the sewage sample. However, this London outbreak is yet more evidence that the long-awaited goal of global elimination of polio is within reach. The sooner it’s stamped out in the two remaining endemic countries, the sooner no child will have to be sickened by it again.

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