Usually, one to three samples of poliovirus are detected in sewage in the UK a year, but the number detected in recent months is concerning

The UK Health Security Agency has reported the detection of several samples of poliovirus in a sewage treatment centre in northeast London over the course of a few months.

The number of samples already raises some alarms; usually, one to three samples would be reported in a year but these viruses are genetically related suggesting that they were spread among a local but extended group.

The London Beckton Sewage Treatment Works, where the sample was collected between February and June 2022, covers a population of 4 million people. The poliovirus in question appears to be a vaccine-derived poliovirus (VDPV2), which is extremely rare.

This is the consequence of low immunization rates in communities receiving the oral polio vaccine.

This vaccine has weakened viruses so that the immune system can learn to fight them, but if the population is not vaccinated and the virus is allowed to spread via water or food contaminated with infected faeces, the weakened virus can mutate into a stronger version.

The UK hasn’t used the oral polio vaccine since 2004, so it is believed that the case was imported from someone who was given the vaccine in one of several countries, such as Pakistan, Afghanistan, or Nigeria, that are using OPV to control outbreaks.

The agency is inviting doctors and medical institutes to check that patients have received their vaccines and that they are immune. Polio can induce muscle weakness, paralysis, and death. Wild polio has been almost completely eradicated from the world, saving thousands of lives.

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