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Comment by mcguire | Hacker News Reader

This whole thing is very concerning.

"According to the New York State Health Department, a person was found to be infected by a vaccine-derived poliovirus type 2 (VDPV2), aka revertant polio Sabin type 2 virus."

"Vaccine-associated paralytic polio" (https://www.cdc.gov/vaccines/vpd/polio/hcp/vaccine-derived-p...) is "a rare adverse event" following immunization with the Oral Polio Vaccine. "The United States exclusively has used IPV since 2000."

I doesn't seem likely that a "young adult" who hasn't travelled outside the US would be exposed to the OPV. Possibly, from some of the other cases mentioned in the CDC article, someone the young adult interacted with had been exposed to it, though.

The original article doesn't mention if the young adult was immunocompromised, which seems like a requirement for a secondary OPV infection.

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This does indeed seem like the unfortunate confluence of being exposed to someone shedding the vaccine-strain and community transmission. Which is exceedingly rare in the U.S., but is entirely foreseeable in low vaccination rate enclaves, which are growing more common.

The risk of spread from weakened virus is completely eliminated under a proper vaccination program. You go into a community, vaccinate everyone, and you have zero risk.

The fact the patient was unvaccinated was effectively their "immunocompromise" that allowed the virus to spread to them.

Unfortunately, vaccinating everyone is not actually zero risk. A small proportion of people who recieve the oral polio vaccine develop vaccine-associated paralytic polio which is exactly what it sounds like - full-on paralytic polio caused by receiving the vaccine. It's a rare complication, somewhere around one in a million, but back when polio had been eradicated in most of the world it was the main cause of paralytic polio. So we'd really like to fully eradicate polio and then stop using that vaccine.

This is made harder by another similar but subtly different problem - circulating vaccine-derived polioviruses. They come from the oral vaccine too, but instead of affecting vaccinated people they spread amongst the unvaccinated population and evolve to regain the virulence and high rate of paralyzation of wild polio. It's one of those viruses that was found in New York. This poses a problem for eradicating polio and stopping vaccination, because once you're no longer vaccinating people they can catch and spread the virus from the oral vaccine and it can evolve into something dangerous. The current VDPV problem traces back to an attempt to finally finish eradicating the type 2 poliovirus, which no longer exists in its wild form, by removing it from the oral vaccine and stamping out any subsequent VDPV spread. This failed badly.

Wikipedia states

> A potential, adverse effect of the OPV is its known ability to recombine to a form that causes neurological infection and paralysis.[27] This genetic reversal of the pathogen to a virulent form takes a considerable time (at least 12 months) and does not affect the person who was originally vaccinated. The vaccine-derived attenuated virus is normally excreted from vaccinated people for a limited period. Thus, in areas with poor sanitation and low vaccination coverage, the spontaneous reversal of the vaccine-derived virus to a virulent form and its spreading in the environment can lead to unvaccinated people becoming infected.

Which boils down to no, you cannot get polio from the polio vaccine but potentially some others could get polio from you for a short period a year later if they’re not vaccinated.

A couple of paragraphs up in the Wikipedia article: "Oral polio vaccine results in vaccine-associated paralytic poliomylelitis in about three per million doses". I've also seen one in two million doses quoted elsewhere, but it's somewhere around the one in a million mark. You coupld probably quibble about whether that really counts as getting polio, but it's paralysis caused by infection with poliovirus and there is "no clinical difference between the paralysis caused by wild poliovirus, OPV, or VDPV" according to the CDC's FAQ on the topic so that's not a particularly interesting semantic quibble to me.

But NOT to the person who was vaccinated

One in 200 infections leads to paralysis. So yes it is effectively zero risk compared to non-vaccination.

If you eliminate the unvaccinated population, vaccine-derived infections are a non-issue. Which is how we addressed the problem prior to 1979 - largely due to the fact that everyone saw first had what the virus did and there was no vaccine hesitancy.

But we haven't used weakened virus vaccines for polio in the last 20 years, so it's kinda moot.

> zero risk

* if you live on a spherical planet with spherical people

And cows.

https://en.wikipedia.org/wiki/Spherical_cow

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