Polio Transmission in London
This week there were alarming reports of polio virus, which can cause paralysis, circulating in London. The detection was made by sampling sewage from Becton. This is worrying because, for 20 years, the UK has enjoyed “polio elimination” status, meaning the disease does not circulate here. But, what’s actually been detected is the genetic signature of polio vaccine, rather than the wild-type disease itself. Nevertheless, this is concerning because we don’t use live polio vaccines here any more, so this must have come in from abroad; and the sustained presence of the agent over many months, which is what’s been found, suggests that it’s found a toe-hold in the community, arguing that not enough people have been vaccinated to stop polio spreading. And if the spreading, weakened vaccine strain mutates into a nastier form, which can happen, we could have a problem. Virologist Wendy Barclay…
Wendy - We've had this announcement from the UK health security agency that some poliovirus has been picked up in sewage samples. So we do this routine surveillance where we look to see what viruses are out there in the water, and it can indicate what viruses might be circulating in a community in a certain place. Whereas we normally pick up very few of these polio viruses. There've now been some reports all the way through from February, till May. There is some vaccine derived polio virus in the sewage samples that have been collected in North and East London. This has caused some alarm because there's more of it than usual and over a longer period than usual, which suggests that there could well be some level of circulation in the community there.
Chris - If it's a vaccine, why are we bothered?
Wendy - The fact that it's a vaccine is interesting in several ways. First of all, we don't use the live oral vaccine against polio virus at all in the UK. We use what's called the inactivated polio virus vaccine. So that tells us that this virus which is circulating has been introduced from somewhere outside of the UK. The fact that it's circulating again is not unheard of, but the fact that it's circulating suggests that actually there are a group of people in whom it's circulating who are not immune to polio, and that's a bad way to be. We don't want there to be groups of people in the UK who aren't immune to polio.
Chris - So we've got really two headaches here in the sense that we've got admittedly vaccine derived polio virus circulating, so it's not just a one off pickup from one person shedding it. The fact that it's been there for months shows that it must be circulating among a group of people. And this shows that there's enough people who are not immune to polio in the immediate area this is happening, that it is clearly transmitting among those people.
Wendy - Yes, that's right. And then the third thing to worry about is that although the live attenuated polio virus vaccine that we have used orally in the UK in the past and is still used in a few places in the world is a good vaccine, it is attenuated as with all viruses, it can mutate. And if it reverts to being fully virulent, what that means is that it's a vaccine derived virus, but it's no longer necessarily completely attenuated and could cause serious illness.
Chris - So what will the public health practitioners who have sounded the alarm now be doing?
Wendy - So what public health agencies will be encouraging people to do is to come forward and get a polio vaccine. They will be offered the inactivated polio virus vaccine, which is widely available in the UK, and that will protect them against any serious consequences of picking up this particular vaccine derived polio virus.