On May 13, 1981, Pope John Paul II survived an assassination attempt in St. Peter’s Square. May 13 is the anniversary of the first apparition of Mary to three peasant children in Fatima, Portugal, in 1917. The Pope later attributed his survival to Our Lady of Fatima. The experience increased his already very strong devotion to Mary.
Even the enthusiastic endorsement of a pope, however, does not make Fatima (or any Marian apparition) a required part of the Catholic faith. All Marian apparitions fit under the category of “private revelation,” which is distinct from “public revelation” (culminating in the teaching of Christ and the apostles). As the Catechism explains,
“Throughout the ages, there have been so-called “private revelations,” some of which have been recognized by the authority of the Church. They do not belong, however, to the deposit of faith. It is not their role to improve or complete Christ’s definitive Revelation, but to help live more fully by it in a certain period of history.” (CCC 67)
In other words, you are not bound to believe that Mary saved Pope John Paul II, nor are you bound to believe that she appeared to the children in Fatima (or anywhere else, for that matter). You are free to believe in all of the Marian apparitions, or none of them, or some of them, according to whichever conclusions you draw from your own study and prayer.