ALL children aged one to nine in London are to be offered urgent polio boosters amid fears that the virus is spreading in the capital, with monitoring due to be stepped up across the UK.
The rollout comes weeks after an unvaccinated 20-year-old man from New York State became the first person in almost a decade in the US to fall ill with paralysis symptoms as a result of polio infection.
Analysis by the World Health Organisation has established that samples of the virus found in sewage in London, New York and Jerusalem are genetically linked.
The UK Health Security Agency said it has identified traces of polio virus 116 times from 19 sewage samples collected in London between February 8 and July 5.
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Sewage samples from Glasgow - which is also routinely included as part of the UK's polio surveillance programme - have all been negative, but the UKHSA is preparing to extend surveillance to 10-15 additional locations in England and further sites in Scotland, Wales and Northern Ireland as part of its public health response.
In an average year, UK surveillance would tend to detect around one to three unrelated polioviruses from sewage, typically linked to individuals coming from abroad who have been vaccinated with the live oral polio vaccine which is no longer used in the UK.
Europe has been polio-free since 2003, and the last UK-acquired case of polio was in 1984.
It is thought that the current transmission may have been encouraged by a dip in childhood vaccination during the pandemic, as mapping shows that positive samples are clustered in communities such as Hackney where as few as 54 per cent of pre-school children have had the booster jag and 61% of 12-month-olds have completed the primary vaccine course.
So far, no cases of polio have been diagnosed, although most people will catch and spread the virus without experiencing any symptoms and people who are fully vaccinated have extremely high protection against the disease.
However, around 0.1-1% of infections in unvaccinated individuals will result in muscular and respiratory paralysis, which is incurable and can be life-threatening.
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The UKHSA stresses that so far, only a small number of the positive samples have been classified as vaccine-derived poliovirus (VDPV2) - as opposed to one-off "vaccine-like" cases associated with the inactivated vaccine used in the UK.
The VDPV2 samples share genetic mutations which suggest the virus is transmitting beyond a close network of a few individuals. This is more like wild-type polio, and could cause severe illness.
Scientists are keen to drive up polio vaccine coverage in London to prevent under-vaccinated children spreading the virus asymptomatically in a way that could increase the risk to unvaccinated children and adults at risk.
In the UK, children are vaccinated against polio using the six-in-one vaccine which is offered at eight, 12 and 16 weeks old, with a booster - the four-in-one vaccine - from three years and four months.
Uptake has tended to be high in Scotland, with 96.1% of 12-month-olds having completed the primary course as of March this year, and 92.4% having had the booster by five-years-old.
The WHO target is for 95% coverage.
Dr Vanessa Saliba, consultant epidemiologist at UKHSA , said: "No cases of polio have been reported and for the majority of the population, who are fully vaccinated, the risk is low.
"But we know the areas in London where the poliovirus is being transmitted have some of the lowest vaccination rates.
"This is why the virus is spreading in these communities and puts those residents not fully vaccinated at greater risk."
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Dr Kathleen O’Reilly, an expert in polio eradication at the London School of Hygiene and Tropical Medicine, said: "These investigations of sewage catchments for poliovirus have been very helpful in understanding the epidemiology of this incident, but also illustrates that circulation is wider than originally thought."
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