Despite the known importance of vaccines as one of the greatest achievements in medical science, vaccine hesitancy has been increasing in the last decade and has become a major threat to global health. The growth of vaccine hesitancy worldwide became more evident with the onset of COVID-19 and raised the fear that this hesitancy would also impact companion animal vaccination. This study aimed to characterize vaccine-hesitant groups regarding companion animals and human vaccinations, as well as to explore the possible association between vaccine hesitancy in pets and their owners. An anonymous online survey containing 27 closed questions was conducted, including questions about dog health, such as vaccination, neutering, and homeopathy use, as well as questions about the COVID-19 vaccination status of the owner and motivations for vaccinating or not vaccinating their pets. Most participants (81.5 %) reported receiving three or more doses of the COVID-19 vaccine. Not vaccinating against COVID-19 or having an incomplete vaccination protocol was associated with an increase in the age range of participants (odds ratio [OR] = 1.43), not having higher education (OR = 7.70), and being in extreme income ranges (less than two minimum wages [OR = 7.57] and more than 10 [OR = 5.20]). The use of homeopathy in humans (OR = 3.24) and dogs (OR = 3.74) was associated with non-vaccination against COVID-19. Owners who were not fully vaccinated against COVID-19 were almost six times more likely to not vaccinate their dogs (OR = 5.94). Non-vaccination of dogs was also associated with non-neutering (OR = 3.56), keeping the dog in contact with other dogs (OR = 2.09), and an increase in the number of dogs in the house increased the chance of not vaccinating the animals (OR = 1.30). The present study revealed a strong association between non-vaccination against COVID-19 and non-vaccination in companion dogs, raising the hypothesis that vaccination hesitancy is a growing challenge in veterinary medicine. In addition, the characteristics of Brazilians who are reluctant to be vaccinated against COVID-19 or immunize their companion animals are described here for the first time.Copyright © 2023 Elsevier B.V. All rights reserved.