[yholio]

I think 'ars' is leading you into a rhetorical trap. The objective was never eliminating the wild virus, the objective was curing polio. The OPV vaccine is a bit like fighting fire with fire: you burn down the forest (immunize susceptible hosts) in a controlled fashion, so that the forest fire cannot reach homes (paralyze children). But when your house burns down, it's irrelevant if it was the "wild" fire or a fire set by the firefighters, i.e a attenuated virus that mutated.

What 'ars' seems to be missing is that this particular "forest" is very rapidly growing back, in some countries you have in excess of 5% of the population as infants each year. Those are new hosts that were never vaccinated, and due to the extreme contagiousness of the disease a few years of lack of coverage can reignite the fire. What happened after OPV2 withdrawal was that a whole new generation inoculated with only bivalent (type 1+3) vaccine became susceptible to cvdpv2 that was still circulating in small pockets.

Essentially, the campaign failed the end-game strategy, they proved they can reduce the infection to arbitrarily low levels using trivalent OPV, but once you take OPV away, as they attempted for a single strain, the epidemic reignites. It's irrelevant if it's a wpv or cvdpv strain. The end-game was always considered a challenge by experts, but a variety of reasons, Covid, political issues etc. conspired to make it very difficult.

This whole thread leaves me very pessimistic about the prospects of eradication. If a relatively inteligent and educated internet-person that has proper sanitation cannot understand these epidemiological dynamics and claims that "OPV causes more infections than it cures", what's the chance you can explain it to rural farmers, especially after the global rise of the antivax movement after Covid?

[ars]

> "OPV causes more infections than it cures"

OPV2 (specifically 2) cures zero infections because type 2 is extinct in the wild. If causes some infections.

So explain how my sentence isn't true?

A decade ago when type 2 was in the wild, OPV2 was very valuable. Today though it's the greatest obstacle to eradication (and not because people are doing something bad, it's just unfortunate circumstance).

[yholio]

> OPV2 (specifically 2) cures zero infections because type 2 is extinct in the wild. So explain how my sentence isn't true?

OPV2 prevents cvdpv2 infections. This is a virus similar in all respects to wpv2, except its lower rate of paralysis onset. It's effectively the same disease, just like in my forest fire analogy.

Before the advent of nOPV2, OPV2 was much more effective at this than any other option. So you could not simply cease OPV2 production, post 2016 it was targeted to cvdpv2 hotspots only.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8393165/

[makomk]

The thing is that we really, really want to be able to stop giving the OPV vaccine because - aside from the fact that it requires a bunch of resources and there's always the risk of disruptions to vaccination from civil wars, other pandemics, etc - the original unmutated vaccine itself paralyzes and even kills a small fraction of the people it's given to, and at low levels of disease those cases can easily become more common than actual polio-related paralysis. That's why it's not used in the developed world anymore.