As I mentioned earlier, all dogs are susceptible to infection when first exposed to the virus because dogs don't have natural immunity to the disease. (criticalcaredvm.com)
This is because the population of dogs in areas where there has been an outbreak develop immunity to the disease by exposure to the virus. (tampabayvets.net)
You need to be prepared for what's ahead and you want to provide your dog with as much immunity to these diseases as possible. (all-about-puppies.com)