It takes up to 14 days for the immune system to complete its response to a modified live virus vaccination for canine viruses. (caberfeidh.com)
This is probably due immunity acquired through canine distemper virus vaccination or exposure to the virus naturally, leading to immunity. (vetinfo.com)
Puppies need parvo virus vaccination starting at about 6 weeks of age and repeating every 3 - 4 weeks until at least 14 - 16 weeks of age. (eastcentralvet.com)