In the 1980s polio was prevalent in countries around the world. The map shows how this changed in just 1 generation https://ourworldindata.org/grapher/the-number-of-reported-polio-cases?tab=map&country=NGA …pic.twitter.com/3CmfNVakGh
It just so happens that the 3 countries that are still in the green are the countries that don't use the polio vaccines 
-
-
That exactly how effective vaccine programs work. Pay attention in school next time.
Thanks. Twitter will use this to make your timeline better. UndoUndo
-
Loading seems to be taking a while.
Twitter may be over capacity or experiencing a momentary hiccup. Try again or visit Twitter Status for more information.