Poliovirus might be spreading in the United Kingdom (UK) after almost 40 years. The UK Health Security Agency (UKHSA) reported finding traces of a vaccine-derived version of the virus in London sewage samples. The health agency's chief warned that it was a national incident.
The last person infected with polio was in 1984, but there have been dozens of imported cases. The UK was finally declared polio-free in 2003. The report came as the nation continued its battle against the rare monkeypox infection.
London Residents Reminded to Get Children Vaccinated
The UKHSA officials found traces of poliovirus in sewage samples they collected from the Beckton Sewage Treatment Works from February to May. According to their report, it was normal to see 1 to 3 vaccine-like polioviruses every year in the UK sewage samples, but they have been one-off findings that were never detected again until now.
The recent sewage samples raised alarms because the virus has continued to evolve and is now classified as "vaccine-derived" poliovirus type 2 (VDPV2).
For now, no polio cases have been reported across the country, and the risk is considered low. However, epidemiologist Vanessa Saliba from the UKHSA said that the public should ensure that their polio vaccinations are up to date.
She said in the report that most UK residents are protected from the virus since childhood, but there are still communities with low vaccine coverage. The health agency urges parents to ensure their children have received the polio vaccine to protect themselves from the virus. There is a global vaccination program underway to eradicate the wild poliovirus.
UKHSA also believes that the virus has been spreading across closely-linked individuals in North and East London based on the findings and they could be shedding the vaccine-derived poliovirus in their feces.
How Did VDPV2 Get Into UK's Sewage?
There are two types of polio vaccines: oral vaccines and inactivated vaccines. According to ARS Technica, several high-income countries are considered polio-free and use inactivated vaccines that do not have viruses capable of replicating or spreading.
Inactiactivated vaccines are highly effective at preventing paralytic polio. However, they do not trigger high levels of immune responses in the gut, allowing wild poliovirus to replicate and spread. On the other hand, oral vaccines do not protect against paralytic polio but can produce strong local immune responses to block the virus from replicating in the gut.
Oral vaccines are cheaper than the inactivated kind, which is one of the reasons they are the predominant vaccines used in the long battle to eradicate polio in many countries. Currently, Afghanistan, Pakistan, Malawi, and Mozambique have recently reported single cases of poliovirus.
Although oral vaccines might seem ideal, the downside is that people vaccinated with them can shed the attenuated vaccine virus in their stool several weeks after getting the vaccine. It is usually the case in communities with poor sanitation, hygiene, and low vaccination rate, wherein the virus could spread from one person to another.
As it spreads to the community, the virus would pick up mutations that make it more like wild poliovirus, regain its ability to cause disease, and sometimes paralyze unvaccinated individuals. It has become VDPV at this point, like the ones detected in several African countries and Israel.
In the UK sewage case, UKHSA believes that someone got vaccinated overseas with the live oral polio vaccine and returned or traveled to the UK and shed traces of VDPV2 in their feces.
RELATED ARTICLE: Africa Once Again Battles Polio Outbreaks After Two Years of Declaring Free From Any of Its Types
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