[Vaccine-associated adverse events in cats]

Owners commonly have certain concerns about vaccinations, particularly regarding potential adverse reactions. This review presents a summary of vaccine-associated adverse events (VAAEs) reported in cats. The most commonly observed VAAEs in cats include mild, non-specific signs such as a mildly reduced general condition, anorexia, and increased body temperature. These mild systemic reactions commonly indicate a good immune response. Severe VAAEs, such as type I hypersensitivity reactions (allergic or anaphylactic reaction), are very rare but potentially life-threatening. They can occur either immediately (within minutes) or several hours later and usually require treatment. The risk of VAAEs increases with the number of applied vaccines per visit. Therefore, a risk-benefit analysis should be carried out for each vaccination, and the number of vaccine components per visit should be minimized. Antibody measurements can be performed to assess the need for re-vaccinations, at least against panleukopenia in adult cats (re-vaccination only if antibodies are lacking). Also, long-term reactions after vaccinations play a role in cats. The most serious VAAE in cats is the feline injection-site sarcoma (FISS), which can develop at injection sites following vaccinations (or other injections). The definitive cause of FISS is still not fully understood. Furthermore, studies have found a potential correlation between (frequent) vaccinations and chronic kidney disease in cats, although a definite causal proof is lacking. Therefore, this principle should always be followed: vaccinate as often as necessary but not more than necessary.