More polio vaccine virus found in sewers

Analysis reveals this weakened virus is evolving, causing worry about its impacts on under-vaccinated groups
12 August 2022

Interview with 

Chris Smith, Naked Scientists


Across London, over a million children aged 1 to 9 will be offered a poliovirus vaccine in the coming months. This has been announced following the detection over a number of months now of poliovirus in sewage samples collected from a number of London boroughs. It indicates spread of the virus in the community, which in turn points to insufficient levels of immunity in the population. Chris Smith told James Tytko about the ongoing situation...

Chris - Going back over the last few months, the sampling - which is done routinely on sewage in London and also carried out in Glasgow - has picked up traces of the genetic material from polio virus, but not what we call the wild type virus -  it's actually vaccine. We've got three different types of poliovirus that we have vaccines against, and they're weakened forms of the virus. They've been grown in a dish and because a dish doesn't have an immune system, if you do this for long enough, eventually you get a virus that forgets how to outwit your immune system and it weakens. So it can show you what polio virus looks like, but it can't make you ill and that's why it's used as a vaccine. But it's not used here anymore. We stopped using live vaccines in this country about 20 years ago. The reason for this is that there is a low risk when you use those live vaccines, that as well as rendering people immune, you are putting back into the environment live poliovirus that can mutate and change and become virulent again; it could cause polio in the future. So we don't use them, but some countries still do specifically those countries where they're still circulating polio. Only a handful of those, thank goodness, nowadays. So what this tells us is that somebody has been to one of those particular risk areas and they've received the polio vaccine, or they have come into contact with it in the environment, they've brought it to the UK, and it's now settled into a community where there's insufficient levels of immunity to polio with the consequence that it is spreading in the community. And what has now spooked public health officials in London is that not only have they detected this, but they've gone on to continue to detect it until most recently in July, and they've also detected now some signs that the virus is changing genetically in a way that would revert it back to a virulent form of polio that could cause paralysis, which used to be a scourge causing thousands of cases of paralysis in younger people about 50 years ago.

James - That's worrying to hear because as far as I knew the UK had eliminated polio. How worried are you? What's the risk of this posing a big threat to public health?

Chris - Well, there are a number of things to be worried about. One of them is the broader picture, which is that if this is circulating and it's circulating in a population that ostensibly have all been vaccinated because we vaccinate our children in this country with a killed form of polio vaccine from the age of when they're born - two, three, and four months you get your first doses of polio vaccine - then a reminder for your immune system at the age of three. And then another reminder, a booster, at 14. This should endow people with comprehensive lifelong immunity against polio. The fact that it is circulating in the community shows that there is inadequate protection from people who probably haven't been adequately vaccinated. So there's probably poor vaccine uptake. And that is born out by the fact that when surveys are done in some of the London boroughs where this is being detected, only 61% of children have been vaccinated. To get the magic herd immunity that we need to stop the virus circulating like this, you need 95% uptake of the vaccine. We're well short of that. So there's a public health situation in terms of vaccination, which means we're also vulnerable probably to other diseases as well if there's lower uptake with other sorts of vaccines. There's also the fact that we have now got the circulation in our community of a form of polio which is live and it could revert into a fully virulent polio capable of triggering cases of paralysis. And that has happened. And in New York, they have detected a young man with actually the same type of polio as we've got here in recent weeks, who has developed some polio symptoms. So the risk is very real.

James - So the next steps, presumably we need to get vaccines in arms. How will that help put a cap on the situation?

Chris - What they are announcing in London in the last day is that a million children up to the age of nine from the age of one will be offered a polio booster. Now it doesn't matter if anyone has already had all of the polio vaccines they should have done, this will merely boost the immunity they've got. But what it will hopefully do is endow those people who have fallen short of adequate protection or have had no protection yet with (a) protection from severe disease. Because if you have all of your polio shots, you have a 99-100% chance that you won't become severely unwell if you do encounter polio. But what it will also do is it will stop the chain of transmission. So we will hopefully reign in this onward transmission we're seeing with the virus in the community, and that will reduce the risk of further incurrences into other populations and possibly this reversion to type where the polio becomes more like it's wild type cousin capable of causing paralysis again.

James - Let's hope we can keep it under control. Chris. Thank you very much.


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