Londoners in 1959 receive their shot of the polio vaccine.Photo: Keystone (Getty Images)
The HSA said in its release that it is typical to encounter one to three polioviruses a year in sewage, but those incidents have been “one-off findings” that occur when a person who was recently vaccinated for polio travels to the country. There were apparently several “closely related” viruses found in sewage in those late-winter and spring months. The polio found in the UK sewers are strains of vaccine-derived poliovirus type 2, or “VDPV2.”
“Vaccine-derived poliovirus has the potential to spread, particularly in communities where vaccine uptake is lower,” said Vanessa Saliba, a consultant epidemiologist for the UKHSA, in the HSA release.
Saliba went on Twitter to discuss the differences between the two types of polio vaccine. One, the injectable kind, has been used in the UK since 2004 and does not include a live virus; the oral kind of vaccine is used in countries where the virus is still circulating. The oral vaccine includes a weakened virus to build up immunity in a patient, but patients may excrete that virus in their stool for weeks after they receive their initial dose. Sometimes this virus can mutate into a strain that more closely resembles the polio found in the wild, which then allows it to spread and cause illness to others, particularly unvaccinated people. That is the vaccine-derived version of polio officials say was located in city sewage.
So how likely is someone who gets VDPV2 to develop debilitating symptoms? A vaccinated person should be well protected from infection and illness, but an unvaccinated person could suffer the same effects as with the wild-type poliovirus. Among unvaccinated people, poliovirus often causes flu-like illness, but in about 1% of cases, the virus attacks nerves in the spine and base of the brain, which can cause paralysis. The virus might also attack breathing muscles, sometimes fatally.
Kids in the UK are supposed to receive their polio shot at 8, 12, and 16 weeks, alongside other early vaccinations. They then receive another pre-school booster when around 3 years old, and another when they’re 14.
Polio, once a widespread and devastating disease, has been driven to near extinction around the world thanks to vaccines. In recent years, only double- or single-digits cases of wild-type polio have been recorded annually. But vaccination rates have been declining in many western nations, including the US Epidemiologists say a population needs to maintain a 95% vaccination rate to prevent reintroduction of the virus. London immunization rates are hovering under 87%, according to the Global Polio Eradication Initiative. The Telegraph reported north Londoners have been particularly bad at getting “the jab,” with approximately one in 10 unvaccinated and 30% unboosted as teens. Within Hillingdon borough in west London, only 35% of teens were boosted against polio.
In the HSA release, the chief nurse for Britain’s National Health Service said that the majority of Londoners are protected against polio, but that the agency is reaching out to parents with children under 5 who haven’t had their kids vaccinated yet.