Low polio vaccination coverage among teenagers risks the re-emergence of virulent polio infection in the UK, experts have warned.
Fewer than half of 13 to 14-year-olds received their teenage booster against polio in some parts of England last year, data shows, after public health officials declared a national incident over evidence the virus is spreading in the community.
The form of virus that was detected through routine surveillance of wastewater in north and east London – vaccine-derived poliovirus – poses a low risk to health but there is a concern that a significant drop in vaccination uptake during the pandemic could offer the virus a foothold, allowing it to keep circulating.
Official data shows that just 35% of 13 and 14-year-olds received polio boosters in Hillingdon, west London, which has the worst coverage in the country. In Brent, 38% of this age group are fully vaccinated and four other London authorities – Westminster, Hammersmith and Fulham, Camden and Ealing – had coverage of lower than 50%.
Although the vast majority of these teenagers will have received primary doses of the vaccine as babies and young children, and will be protected against serious illness, low coverage makes infection more likely.
Prof Paul Hunter, of the University of East Anglia, said: “Teenagers are not necessarily that well-protected against infection, particularly if they’ve not had the booster. We’re not expecting it to give rise to paralytic cases over the coming days, but the longer it circulates the more opportunity there is for it to turn into a fully virulent polio virus again, which would be a disaster. Those places with low uptake need to urgently address it.”
Across England for 2020-21, coverage in just 15 out of 146 local authorities (11%) was above 90%. The UK does not have a formal target for teenage booster uptake, but the World Health Organization sets an overall population target of 95% for full vaccination.
The polio alert by the UK Health Security Agency on Wednesday followed tests on wastewater from the Beckton sewage treatment works in Newham, which covers a population of 4 million in north and east London.
The agency typically picks up a handful of unrelated positive results for poliovirus each year, linked to people given the oral polio vaccine in other countries. The oral vaccine contains live virus – unlike the inactivated vaccine given in the UK – and people can shed this in their faeces for several weeks and also infect others.
The London samples raised the alarm because they were related to one another and contained mutations that suggested the virus was evolving as it spreads from person to person. If it continues to spread, vaccine-associated virus can mutate to become fully virulent, to the point where it can cause paralysis in unvaccinated people.
“It’s not a thing that happens from this week to next week,” said Prof Beate Kampmann, director of the Vaccine Centre at the London School of Hygiene & Tropical Medicine. “It’s multiple passages through a lot of people. If you have a lot of virus circulating, the chances of it mutating is higher.”
She said that relatively low rates of uptake left the UK “vulnerable” to such a scenario.
Health officials are now working to establish how much the virus has spread – it may be confined to a single household or an extended family – and a more precise geographical location.
Health minister Lord Kamall, questioned on the issue in the House of Lords, said public health experts hope to “go along the pipe” to trace the source.
“It is mixed up with a lot of other stuff. And what we’ve got to try and work out now is how we go along the pipe, as it were, and investigate individual pipes, to see whether we can locate the source. And in theory, it might be possible to find individual households or streets.”
He confirmed that public health experts believe the samples originated from someone vaccinated abroad. “It probably came from someone who had the oral polio vaccine overseas, came to the UK and excreted it into the system,” he said.
The government and NHS are encouraging parents to ensure their children are up to date on their jabs, and urging people of any age who have not received the polio vaccine to come forward.