A Dec. 13 article in Fortune called the polio vaccine used in the U.S. today “not only safe but also effective.”

The article also claimed that because 3 billion children have been vaccinated against polio since 1988, according to the Global Polio Eradication Initiative, that means “20 million people who would’ve otherwise been paralyzed by polio are walking today.”

How accurate is the 20 million figure?