I really had to double check this, and everywhere I check it's the same. Let's compare notes to the question asked "Why is Polio still around today?"
Polio is most prevalent in Egypt, Pakistan and Nigeria.
Factors include:
Misinformation by Militants saying the vaccine is anti-Islam - saying it has pig fat in it... (Translation: In first world countries, they use the computer chip excuse.)
Political Unrest
Negligent Government (Kinda falls under Misinformation by Militants)
Poor Health Infrastructure.
So, basically America at the start of the pandemic in March, 2020.
Do you have an article you'd like to post if it suggests something different?