Objective To determine whether client-owned dogs in Australia, last vaccinated with Canvac (R) vaccines containing canine parvovirus-type 2 (CPV-2), canine distemper virus (CDV), canine adenovirus type 2 (CAV-2) +/- canine parainfluenza virus (CPiV) at least 18 months ago, were seropositive or responded serologically to revaccination. Methods A total of 235 dogs were recruited from 23 veterinary clinics, representing a variety of breeds, ages and time since last vaccination (TSLV: range 1.59 years, mean 2.8 years). Dogs had a blood sample taken and were revaccinated on day 0. A second blood sample was taken 714 days later. Blood samples were assessed for antibody titres to CPV-2 (by haemagglutination inhibition) and CDV, CAV type 1 (CAV-1) and CPiV (by virus neutralisation). Dogs with a day 0 titre >10 or a four-fold increase in titre following revaccination were considered to be serological responders. Results The overall percentage of dogs classified as serological responders was 98.7% for CPV-2, 96.6% for CDV, 99.6% for CAV-1 and 90.3% for CPiV. Conclusions These results suggest that the duration of serological response induced by modified-live vaccines against CPV-2, CDV, CAV-1 and CPiV, including Canvac (R) vaccines, is beyond 18 months and may extend up to 9 years. Accordingly, these vaccines may be considered for use in extended revaccination interval protocols as recommended by current canine vaccine guidelines.