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Vaccine-associated adverse events in dogs are far less common today

a dog at the vet

Dogs rarely experience adverse events after receiving vaccinations. Banfield Pet Hospital and Purdue University’s College of Veterinary Medicine first analyzed the incidence and possible risk factors of vaccine-associated adverse events (VAAEs) in dogs from 2002 to 2003 to inform veterinary risk assessment and client communication regarding vaccination. We recently completed a similar analysis of canine VAAE incidence and risk factors from 2016 to 2020 to find out what has changed in 15+ years. We shared the results at the 2022 American College of Veterinary Internal Medicine Forum in Austin, TX. Overall, 18.4 VAAEs occurred for every 10,000 dogs vaccinated in 2016 to 2020, less than half the incidence of 38.2 VAAEs per 10,000 dogs vaccinated in 2002 to 2003. Smaller dogs and those receiving multiple vaccines in the same visit were more likely to experience a VAAE. The large drop in overall incidence of VAAEs over time suggests that newer vaccines are safer than ever, and the variation in incidence among breeds suggests that genetic factors may influence risk the most.

What this means for veterinary teams
Our analysis can help veterinary teams provide quality care to pets in two ways. First, the up-to-date statistics on the low incidence of VAAEs can empower veterinary professionals to alleviate client concerns about adverse events that might otherwise lead them to decline or delay vaccinations, leaving their dogs vulnerable to preventable infectious diseases. Second, understanding the risk factors for VAAEs in dogs allows teams to tailor their care to minimize each pet’s risk.

Incidence of VAAEs in dogs
Our previous analysis of canine VAAE incidence and possible risk factors considered 1,226,159 dogs vaccinated at 360 Banfield Pet Hospitals during 2002 and 2003[1]. We searched their electronic medical records for possible VAAEs (nonspecific vaccine reaction, allergic reaction, urticaria, or anaphylaxis) diagnosed within 3 days after vaccine administration. The overall incidence of VAAEs was 38.2 per 10,000 dogs vaccinated.

Our recent analysis was similar but included about four times as many dogs (almost 5 million) vaccinated at more than 1,000 Banfield hospitals from 2016 to 2000. VAAE incidence was less than half that in the previous study: only 18.4 per 10,000 dogs. Our vaccine suppliers have been committed to product safety and continuous improvement in their manufacturing processes. We believe that the drastic reduction in VAAEs might suggest that new vaccines have better safety profiles.

Risk factors for VAAEs in dogs
Breed and size
Though low overall, the incidence of VAAEs differed somewhat in dogs of different breeds and sizes. VAAE incidence was higher than the overall rate of 18.4 per 10,000 in 10 breeds, and the highest rates were seen in dogs that are relatively small in size. Five reported breeds among the highest VAAE incidence were miniature Dachshund, Boston terrier, miniature Pinscher, French bulldog, and Italian Greyhound. On the other hand, many of the breeds with comparatively low VAAE incidence are relatively large in size, including German shepherd, Labrador retriever, golden retriever, and Rottweilers. Similarly, VAAE incidence was highest in dogs weighing less than 5 kg and the risk of an adverse event generally decreased with increasing dog weight. The lowest rates were seen in dogs weighing greater than 40 kg. These data suggest that patient-related factors significantly influence risk of VAAEs and that genomic analysis might be useful in identifying specific genetic risk factors. As the next phase of our research, we are partnering with our ecosystem colleagues at Wisdom Panel, to investigate the population of ‘reactive’ and ‘non-reactive’ pets to see if genetic mutations or markers may be found that might predict an individual animal’s risk of reaction.

Number of vaccines
Another risk factor for VAAEs was the number of vaccines administered during a single visit, particularly for small dogs. VAAE incidence was greater than the overall rate of 18.4 per 10,000 when 2–5 vaccines were administered at the same appointment. These findings suggest that limiting the number of vaccines administered during an office visit might help to minimize risk of VAAEs, particularly for small dogs.

Both our initial and recent analyses showed that small-breed dogs receiving multiple vaccines in a single visit are at greatest risk of experiencing a VAAE within 3 days of the vaccination. Unlike the risk factors for VAAEs in dogs, however, incidence has not remained similar over the past 15 years. Dogs today are about half as likely to experience a VAAE, likely reflecting safety improvements in vaccine formulations. Additional analysis is planned to further define the ‘at risk’ population. We encourage owners to discuss scheduling of vaccines with their veterinary team, especially for small dogs (who show a higher risk of adverse events) and young dogs (who may need multiple booster vaccinations as they develop and build their immunity).

[1] Moore, G. E., Guptill, L. F., Ward, M. P., Glickman, N. W., Faunt, K. K., Lewis, H. B., & Glickman, L. T. (2005). Adverse events diagnosed within three days of vaccine administration in dogs. J Am Vet Med Assoc 227(7), 1102-1108.