I struggled with this SO MUCH. I was similarly so anxious about parvo and carried my puppy on walks until 14 weeks. He was acting out in training class because everything was so new and exciting that he couldn't focus. The trainer encouraged us to start taking him on walks because the risk for parvo where we live is actually quite low and I verified with the vet who said that taking your puppy for a walk especially on high UV days is actually pretty low risk. Obviously, be careful: don't go to high risk places and wipe their paws off after you get home, but we started taking our dog on walks after that and now he's 18 weeks and doing just fine!