How can dogs still catch parvovirus even if they've been vaccinated?

Hello, Yes, the environment is the direct source of contamination because parvovirus is an incredibly hardy 'naked' virus: it can survive for over a year in soil and grass and is able to withstand both freezing temperatures and heat. If your dogs caught it, it is because the virus was present in their environment, likely in the faeces of infected dogs or brought in on the soles of shoes. Although your two dogs are now immune, your garden remains highly contagious. Please note that disinfection (using bleach, for example) is ineffective on soil and lawns; it only works on hard surfaces like driveways, provided it is left to sit for 10 minutes. As a precaution, I would advise you not to have any other dogs or puppies in your home for at least a year, to give the virus time to die out naturally. Kind regards, Laure.