There are two varieties/technologies of polio vaccine in current use worldwide. The vaccine approved for use in the US is not a live virus vaccine. The non-paralyzing (= weakened) live virus vaccine is cheaper to produce is is used in more cost-sensitive areas, such as Africa. With this vaccine, the weakened virus infects the recipient, whose immune system "learns" how to recognize and fight the wild polio virus. During the time the recipient is infected there is a time period in which they are shedding the virus in their BMs. In areas where waste disposal and hygiene are rudimentary or worse, this weakened virus can spread to random unvaccinated people.
The variety of polio virus that has been detected in NY and in the London England area is of the live virus vaccine type. Because this vaccine is not used in the US, it means that it came to the US via a recently vaccinated person from a third world country or an unvaccinated US resident who got infected while visiting a third world country. Figuring out the continent of origin may be a bit difficult or impossible, since both the London and NYC areas have several international airports and are major hubs for worldwide travel.
The dangers of the weakened virus are with people in poor health and that over the course of several hosts, the weakened virus could mutate into a less benign variant.
And now I have an Over-Explainers Annoymorous meeting to lead,
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