# New-Onset and Flare Episodes of Adult-Onset Still's Disease Following COVID-19 Vaccination: A Systematic Review of Published Case Reports

## TL;DR

This review summarizes 13 cases where adult-onset Still's disease started or worsened after a COVID-19 vaccine, highlighting the need for more research.

## Contribution

The study systematically compiles and analyzes case reports linking AOSD episodes to COVID-19 vaccination.

## Key findings

- Symptoms appeared 4-15 days after vaccination and included fever, arthritis, and high ferritin.
- All patients improved with corticosteroids, some needing biologics.
- No causal link to vaccination was established due to lack of comparative data.

## Abstract

This systematic review provides a descriptive synthesis of published case reports documenting new-onset or flare episodes of adult-onset Still’s disease (AOSD) temporally occurring after COVID-19 vaccination. A comprehensive search of PubMed, Scopus, Web of Science, and Google Scholar identified 13 eligible case reports published between 2020 and 2024. Because all available evidence consisted solely of individual case descriptions without comparator groups, the review followed PRISMA 2020 guidelines and employed qualitative narrative synthesis rather than meta-analysis. Across the included cases, patients consistently presented with hallmark features of AOSD, including high spiking fever, arthritis or arthralgia, markedly elevated ferritin levels, and, in several instances, the characteristic salmon-colored rash. Symptom onset typically occurred within four to fifteen days following vaccination. Although these cases demonstrate recognisable clinical patterns, the absence of denominator data, lack of population-based studies, and inherent publication bias prevent estimation of incidence or risk, and no causal relationship with vaccination can be inferred. All reported patients responded favorably to corticosteroids, with some requiring biologic therapy for disease control. These findings highlight the importance of clinician awareness when evaluating persistent febrile or inflammatory symptoms in recently vaccinated individuals, while emphasising that COVID-19 vaccination remains overwhelmingly safe. Larger registries, pharmacovigilance data, and controlled studies are needed to clarify potential risk factors and guide future revaccination decisions.