We take Parvo very seriously! This is why we use concrete surfaces for the first few weeks. The quickest way to endanger a puppy with this killer virus is to let them roam on grass and soil, where the virus can live for over a year. Once beyond the "danger zone" of 8 weeks (for vaccinated puppies) they can be exposed to other areas as normal. For this (and other reasons) any reputable breeder would never rehome a puppy sooner that 8 weeks.
Our puppies are vaccinated early for Parvo and their kennel is power-washed daily. We even wear hospitable shoe coverings when tending and feeding them. Most vaccinations are done on-site to avoid early exposure in vets office.
Before 8 weeks: