Patrick Mahomes says he's fully vaccinated ... telling reporters Monday he took the shots in the arm to try to help ensure his newborn baby daughter stays healthy.

"To me, it was more of a personal decision with having a baby girl and knowing that I was going to be around people," the NFL superstar said.

"I wanted to make sure I could do whatever I could to help keep her healthy."

Mahomes and his fiancee, Brittany Matthews, welcomed little Sterling Skye Mahomes back in late February ... and Patrick clearly didn't wrestle too much with the decision to get vaccinated as a new dad.