Only bishops Aloisio Riccio and Edward Fitzgerald dissent in the final vote; sixty other bishops who are also opposed have left Rome in order to not be associated with the vote in any way.
Although the formal definition is created in 1870, the idea existed earlier, and Catholics are supposed to believe that it's a revelation of a truth rather than a creation of the Church. Therefore, earlier papal teachings can be labeled "Infallible" if they meet certain conditions.
The dogmatic definition of papal infallibility says that a pope has "full and supreme power of jurisdiction over the whole Church" and when he
"speaks ex cathedra, that is, when, in the exercise of his office as shepherd and teacher of all Christians, in virtue of his supreme apostolic authority, he defines a doctrine concerning faith or morals to be held by the whole Church, he possesses, by the divine assistance promised to him in blessed Peter, that infallibility which the divine Redeemer willed his Church to enjoy in defining doctrine concerning faith or morals."
Thus papal infallibility doesn't mean that a pope is infallible in absolutely everything he says or does. Instead, certain conditions must exist first: he must be speaking "ex cathedra," and he must be speaking on something specific to the faith or morals of the church.
This assertion of papal infallibility will create a great deal of controversy, both inside and outside the Catholic Church. Many Catholics will abandon the church because of it, including some leaders.
Many non-Catholics will criticize the Vatican and Pope Pius IX for assuming far too much authority and power for themselves.