(1) Background: No information is available on how dogs with hypothyroidism (HypoT) respond to vaccination. This study measured pre- and post-vaccination anti-canine parvovirus (CPV) antibodies in dogs with HypoT treated with levothyroxine and compared the results to those of healthy dogs. (2) Methods: Six dogs with HypoT and healthy age-matched control dogs (n = 23) were vaccinated against CPV with a modified-live vaccine. Hemagglutination inhibition was used to measure antibodies on days 0, 7, and 28. The comparison of the vaccination response of dogs with HypoT and healthy dogs were performed with univariate analysis. (3) Results: Pre-vaccination antibodies (≥10) were detected in 100% of dogs with HypoT (6/6; 95% CI: 55.7-100) and in 100% of healthy dogs (23/23; 95% CI: 83.1-100.0). A ≥4-fold titer increase was observed in none of the dogs with HypoT and in 4.3% of the healthy dogs (1/23; CI95%: <0.01-22.7). Mild vaccine-associated adverse events (VAAEs) were detected in 33.3% of the dogs with HypoT (2/6; 95% CI: 9.3-70.4) and in 43.5% (10/23; 95% CI: 25.6-63.2) of the healthy dogs. (4) Conclusions: There was neither a significant difference in the dogs' pre-vaccination antibodies (p = 1.000), or vaccination response (p = 0.735), nor in the occurrence of post-vaccination VAAEs (p = 0.798). The vaccination response in dogs with levothyroxine-treated HypoT seems to be similar to that of healthy dogs.
Keywords: CPV; MLV; T4; immunosuppression; levothyroxine; protection; titer.