My vet was part of a world wide inoculation study that determined dogs do not need the parvo booster and in some cases can result in the deaths of dogs. He now tells his clients that their dogs don’t need the booster and has stopped sending out reminders. BUT he advices people like me, farmers etc to have the parvo jab every 2 years as the efficacy wears off and the disease mutates meaning you need to have a new jab every two years.