I don’t think even Bill Gates was counting on something as devastating as what is happening in Venezuela at the moment. His charity needs minimally functional countries to be able to access all children.
Secondly, Bill Gates was vaccinating only in countries where polio is endemic. His whole thing is once it's gone, it shouldn't come back.
The latest UN HDI data is from 2016 - things have gone /drastically/ downhill for Venezuela since then, especially in the last 6 months.