Vaccine-derived polio is on the rise. A new vaccine aims to stop the spread

https://www.npr.org/sections/goatsandsoda/2022/04/26/ [login to see] /vaccine-derived-polio-is-on-the-rise-a-new-vaccine-aims-to-stop-the-spread
Is polio making a comeback?

The world has spent billions of dollars over the last 15 years in an effort to wipe out the virus through vaccination efforts – with encouraging results.

Rates plunged from an estimated 350,000 cases in 1988 to just several dozen by 2016.

But in recent years, polio incidence has started to inch back up. The reason has to do with the type of vaccine used in many parts of the world, primarily in low- and middle-income countries. While the United States and other Western countries inject an inactivated virus that poses no risk of spread and are now polio-free, other countries rely on an oral vaccine. It's cheap, it's easy to administer and two or more doses confer lifelong immunity. But it's made with living, weakened virus. And that poses a problem.

Those who've been immunized with live virus can shed it in their stool, which can then spread through sewage in places with poor sanitation. If the virus stays weak, it can even expose the unvaccinated to polio and give them immunity. But if it mutates and regains virulence, someone who isn't vaccinated can become sick with vaccine-derived polio after contact with the contaminated wastewater.