ETA.... Parvo is horrible where I live. I just wanted to throw that out there
Distemper and Parvo are more prevalent in the south, but can be found anywhere. They are transmitted through contact with the feces of an infected animal. Pets that have been vaccinated against it shouldn't be a worry, just be concerned with areas that many dogs are using as a potty. It could even be in your own front yard!
Puppy classes are wonderful, I have taken every dog that has ever been in my care through classes and I'm a trainer!
I would allow pups to start my classes at 8 weeks after their first round of shots. I checked all dogs vaccination records before they could enter my training class room. No unvaccinated dogs were allowed in, ever, never ever. It would put my pups at risk. I always bleached my class floors at least once a week too, and would tell puppy owners not to let the pups walk around outside. Never had a problem. Most good training places are the same. Ask before you sign up for a class.
My Aunt's 2 rescue pups had parvo and both survived. It was so terrible! Many dogs don't make it. They had to be hospitalized and quarantined, and missed the period of socialization. She has done tons of training since but both have serious issues with other dogs, children, strangers, loud noises, ect. They are big dogs and if anything happened to my Aunt they would have no where to go. Most likely they would be euthanized.
I think a dogs physical health and mental health are equally important. My advice is research and follow your gut. Good luck lady!