Adult-onset Still's Disease after BNT162b2 mRNA COVID-19 Vaccine.

The coronavirus disease 2019 (COVID-19) pandemic is being overcome by widespread inoculation with various COVID-19 vaccines, but concerns about the safety of the vaccines are a major hurdle to widespread vaccination. We report the first case of adult-onset Still's disease (AOSD) developing in a 36-year-old, previously healthy woman after the first dose of BNT162b2 mRNA COVID-19 vaccine (Pfizer). She visited our hospital due to high spiking fever and sore throat that developed 10 days after vaccination. Based on thorough investigations and changes in symptoms and signs after admission, she was diagnosed with AOSD and treated with high dose steroids and tocilizumab. This report suggests the possibility that AOSD could be triggered by COVID-19 vaccines through activation of the innate immune system.