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If you understand the limitations of the two types of vaccines, this story is just something that should be expected to happen. Someone traveled from a country

If you understand the limitations of the two types of vaccines, this story is just something that should be expected to happen. Someone traveled from a country where the weakened live version is given to the UK. This live version mutated in that individual to become transmissible (this mutation happens in around one in a million individuals). The UK vaccinates with the non-live version. This non-live version cannot mutate, but it is non-sterilizing- the vaccinated can still become infected in their gut- the vaccine prevents it from getting into their bloodstream and become poliomyelitis. We now we see this outcome in the sewage samples.

lamontcg 4y ago
TWiV was discussing this concept awhile back and mentioned the fact that if someone looked for poliovirus in NYC sewer samples that it would certainly turn up. There's a sort of ethical problem here because if you find it you immediately make a big splash and headlines over something entirely expected and not terribly worrisome. They were leaning towards that you just shouldn't look for it -- it doesn't really add anything to science because virologists who study polio knew it'd be there and everyone else would freak out. Well, now we're there more or less.
makomk 4y ago
It's not even really that the live version mutated to become transmissible, exactly - the live oral polio vaccine is reasonably transmissible through the usual fecal-oral route full stop. The problem is that as it spreads through a community the vaccine virus - and especially the type 2 poliovirus - tends to mutate in ways that undo the attenuation which allows it to safely be used as a vaccine and cause it to spread, paralyze and kill in the same way that wild-type polio virus does. Viruses with these kind of mutations have been circulating in the developing world for some time and there seems to be concern they may now be in the UK. (In fact this is the only kind of type 2 poliovirus in circulation these days - the wild version of it was eradicated a few years ago. There were a bunch of celebratory announcements of this that made it to HN which were probably rather premature. The WHO and their partners had a fancy endgame plan for this involving pulling the type 2 component of the vaccine, at which point it would go extinct for real and we'd no longer have to deal with it. This plan failed spectacularly.)
- gregwebs 4y ago
  Thank you for the correction! That point is made very clear here: https://polioeradication.org/polio-today/polio-prevention/the-vaccines/opv/ https://polioeradication.org/polio-today/polio-prevention/th... It is listed as both a pro (initially free vaccination for anyone that it gets transmitted to) and a con (once it mutates to become neurovirulent. Now that I have some understanding of the limitations of the vaccines the idea that polio will actually be eradicated seems implausible unless we switch everyone over to the live form. I don't pretend to fully understand the subject, but the articles about cases of polio popping up seem to fit my mental model better than the one that expects to eradicate it.

lamontcg 4y ago

TWiV was discussing this concept awhile back and mentioned the fact that if someone looked for poliovirus in NYC sewer samples that it would certainly turn up. There's a sort of ethical problem here because if you find it you immediately make a big splash and headlines over something entirely expected and not terribly worrisome. They were leaning towards that you just shouldn't look for it -- it doesn't really add anything to science because virologists who study polio knew it'd be there and everyone else would freak out. Well, now we're there more or less.

makomk 4y ago

It's not even really that the live version mutated to become transmissible, exactly - the live oral polio vaccine is reasonably transmissible through the usual fecal-oral route full stop. The problem is that as it spreads through a community the vaccine virus - and especially the type 2 poliovirus - tends to mutate in ways that undo the attenuation which allows it to safely be used as a vaccine and cause it to spread, paralyze and kill in the same way that wild-type polio virus does. Viruses with these kind of mutations have been circulating in the developing world for some time and there seems to be concern they may now be in the UK. (In fact this is the only kind of type 2 poliovirus in circulation these days - the wild version of it was eradicated a few years ago. There were a bunch of celebratory announcements of this that made it to HN which were probably rather premature. The WHO and their partners had a fancy endgame plan for this involving pulling the type 2 component of the vaccine, at which point it would go extinct for real and we'd no longer have to deal with it. This plan failed spectacularly.)

gregwebs 4y ago
Thank you for the correction! That point is made very clear here: https://polioeradication.org/polio-today/polio-prevention/the-vaccines/opv/ https://polioeradication.org/polio-today/polio-prevention/th... It is listed as both a pro (initially free vaccination for anyone that it gets transmitted to) and a con (once it mutates to become neurovirulent. Now that I have some understanding of the limitations of the vaccines the idea that polio will actually be eradicated seems implausible unless we switch everyone over to the live form. I don't pretend to fully understand the subject, but the articles about cases of polio popping up seem to fit my mental model better than the one that expects to eradicate it.