The incidence of vaccine-associated sarcomas in cats: a systematic review and meta-analysis.

FISS remains rare (~1 per 10,000 vaccinations), supporting continued routine feline vaccination with transparent risk communication.

This systematic review and meta-analysis evaluated the incidence of feline injection-site sarcoma (FISS) following vaccination, synthesizing data from eight eligible studies encompassing over 14 million vaccinations and 411 confirmed FISS cases. The pooled incidence estimate was 8.8 FISS cases per 100,000 vaccinations (95% CI: 0.8–100.6), approximating 1 case per 10,000 vaccinations. Extremely high between-study heterogeneity (I² = 99.61%) was identified, attributable to variation in study design, surveillance methodologies, and case reporting practices. Subgroup analyses comparing pre- and post-2000 studies revealed no statistically significant difference in incidence; however, a trend toward lower incidence in more recent studies suggests that the transition to non-adjuvanted vaccines may have contributed to a reduction in FISS occurrence. Overall certainty of evidence was rated as very low under the GRADE framework, primarily due to high risk of bias across included studies and considerable imprecision in the pooled estimate. Despite these limitations, the findings consistently support FISS as a rare adverse event. The authors conclude that the low absolute incidence reinforces the benefit-risk balance in favor of routine feline vaccination. Improved post-market surveillance systems and more rigorous epidemiologic studies are needed to generate higher-quality incidence data. Clinicians should continue recommending routine vaccination while communicating FISS risk transparently to cat owners and adhering to current best practices regarding injection site selection and rotation.

This summary was distilled by AI and may occasionally misinterpret data. Confirm critical details with the primary literature before clinical application.