Vaccines are the most frequently administered veterinary procedure. Every dog that walks into a clinic for an annual exam, every puppy starting its series, every horse heading to a show — vaccination is routine. But "routine" does not mean "risk-free."

The FDA Center for Veterinary Medicine (CVM) publishes adverse-event report data through the openFDA platform. This article isolates the vaccine and biologic reports from 1.34 million total records and analyzes 3,225 reports where a vaccine or biologic was the sole product involved — no concurrent drugs, no combination parasiticide products. Every number below comes from a direct computation of the FDA CVM animal adverse-event reports filtered to vaccine and biologic products only (analysis run date: 2026-06-10).

Three things these numbers do not mean

Before the data, three caveats that apply to every pharmacovigilance analysis:

1. Reports are not causal proof. The FDA states explicitly that reports in this database have not been verified for causality. A report linking a rabies vaccine to anaphylaxis does not prove the vaccine caused the reaction — it means someone reported a temporal association.
2. Volume reflects usage. Core vaccines (DA2PP/DHPP) are administered far more frequently than Lyme or canine influenza vaccines. More doses given means more reports, regardless of per-dose risk.
3. Under-reporting is substantial. The FDA acknowledges that only a fraction of adverse events are ever reported. Mild injection-site swelling that resolves in 24 hours is rarely reported. The database skews toward more severe and more memorable events.

Identifying vaccine reports

The FDA CVM adverse-event database contains 1,340,077 total records. We applied a two-step filter:

1. Inclusion: The active-ingredient field contained vaccine-related terms (rabies vaccine, bordetella, distemper, parvovirus, adenovirus, leptospira, panleukopenia, calicivirus, rhinotracheitis, feline leukemia, toxoid, bacterin, and related terms).
2. Exclusion: We removed records that also named non-vaccine drugs (NSAIDs, parasiticides, antibiotics, corticosteroids, and other pharmaceuticals) to isolate vaccine-only events.

After filtering, 3,225 reports (0.24% of total records) involved vaccine or biologic products alone.

Which vaccines are reported

Core combination vaccines (canine distemper, adenovirus, parvovirus, parainfluenza) account for 44% of reports — expected given their universal administration to puppies and dogs. Rabies, another universally administered vaccine, accounts for 19%.

The "other" category (24%) includes reports where the ingredient description did not match specific vaccine categories — multi-valent livestock vaccines, autogenous bacterins, and reports with generic ingredient descriptions.

Which species are affected

Cattle dominate at 51% — driven primarily by livestock vaccine reports, including respiratory and reproductive disease vaccines where large herd sizes mean more animals are exposed and more events are observed. Dogs and cats together account for 37%, which aligns with the companion-animal vaccination volume.

The 11 human reports represent accidental needle-stick injuries or self-injection events reported through the veterinary adverse-event system.

The reactions reported

The most frequently reported reaction is death (38.1% of reports). This is striking but must be interpreted carefully. The FDA database captures the most severe and most reportable events — mild reactions are dramatically under-reported. In livestock, a dead animal after vaccination is highly visible and economically significant, motivating reporting. In companion animals, pet owners and veterinarians are more likely to report fatal outcomes than transient injection-site swelling.

Anaphylaxis appears in 5.3% of reports — a clinically important signal that warrants awareness of emergency protocols whenever vaccines are administered.

The outcomes

Outcomes can be multiple per report, so the percentages exceed 100%. The "died" outcome at 44.9% is the combined figure including both natural death and euthanasia-related outcomes. The high "outcome unknown" rate (35.3%) reflects the reality that follow-up is often incomplete — particularly for livestock where the owner or producer may not report back to the veterinarian.

The recovery rate of 24% means roughly one in four animals with a reported adverse event recovered fully. This is an important context point: most vaccine adverse events that are reported are serious, but among those where outcome is known, a substantial portion resolve.

Serious adverse events

The FDA flags reports as "serious" or "not serious." Among vaccine-only reports:

Seven in ten vaccine adverse-event reports are classified as serious. This is a much higher serious-event proportion than drug-specific analyses in the same database (for comparison, the serious-event rate for NSAID reports is lower). This does not mean vaccines are more dangerous than drugs — it means the reporting threshold is higher. Veterinarians and owners tend to report vaccine events only when they are severe enough to notice, whereas drug events (particularly for chronic medications like NSAIDs) are more systematically captured.

Year trend

The upward trend from 2011 to 2025 reflects growing awareness of the reporting system, increased vaccine administration, and possibly the effect of social media making adverse events more visible to pet owners. The relatively stable plateau from 2019 onward (200–340 reports per year) suggests the system has reached a steady-state detection level.

Dog breed patterns

Among the 626 canine vaccine reports where breed was recorded:

Small breeds appear disproportionately represented relative to their population share. Chihuahua, Dachshund, Shih Tzu, Pug, and Yorkshire Terrier together account for 103 of 626 reports (16.4%). This aligns with research from Banfield Pet Hospital showing that vaccine-associated adverse event incidence is highest in dogs under 5 kg and decreases with increasing body weight. Small dogs are not necessarily more immunologically reactive, but the same antigen dose in a smaller body may produce a stronger inflammatory response, and small-breed genetics may include risk factors.

What this means for veterinary practice

Separate vaccines by at least 2–3 weeks when possible. The Banfield data showed that administering multiple vaccines at the same visit increases adverse-event risk, particularly in small dogs. For patients under 5 kg, limiting the number of vaccines per visit is a reasonable precaution.

Be prepared for anaphylaxis. At 5.3% of reports, anaphylaxis is not rare in the context of vaccine adverse events. Emergency drugs (epinephrine, diphenhydramine, dexamethasone SP) should be immediately accessible in the vaccination area, and staff should be trained to recognize early signs.

Report adverse events. The FDA explicitly encourages reporting. Under-reporting means the data underestimates the true frequency of events. Every report strengthens the signal-detection system that protects animals and informs label updates.

Discuss risk honestly with clients. Pet owners deserve to know that vaccines — like all medical interventions — carry risk. The risk is low per-dose but not zero. Frame the conversation around the benefit-risk ratio: the diseases prevented (parvovirus, rabies, distemper) are far more dangerous than the vaccine reactions, but the owner should know what to watch for in the 24–48 hours after vaccination.

Sources

• FDA Center for Veterinary Medicine. Animal drug adverse event reports (openFDA). https://www.fda.gov/animal-veterinary/product-safety-information/adverse-event-reports-animal-drugs-and-devices
• Banfield Pet Hospital / Banfield Exchange. "Vaccine-associated adverse events in dogs are far less common today." https://www.banfieldexchange.com/News/Vaccine-associated-adverse-events
• USDA APHIS Center for Veterinary Biologics. Adverse event reporting for veterinary biologics (vaccines). https://www.aphis.usda.gov/veterinary-biologics
• Moore GE, et al. Adverse events diagnosed within three days of vaccine administration in dogs. JAVMA 2005; 227(7): 1102–1108. https://pubmed.ncbi.nlm.nih.gov/16220670/
• Tizard IR. Adverse consequences of vaccination. In: Vaccines for Veterinarians. Elsevier; 2021. https://pmc.ncbi.nlm.nih.gov/articles/PMC7348619/