Long-Term Autoimmune Polyarthritis due to COVID-19 Vaccine.

Background: Vaccinations for COVID-19 have played a pivotal role in controlling the global pandemic, with most adverse events being mild and transient. However, rare post-vaccination autoimmune responses have been reported. The understanding of long-term rheumatologic sequelae, particularly autoimmune polyarthritis following COVID-19 vaccination, remains limited. Case Presentation: We report the case of a 41-year-old previously healthy man who developed progressive polyarthritis and systemic symptoms following the Johnson & Johnson COVID-19 vaccine. The initial symptoms of joint swelling and arthralgia appeared within a week of the first vaccine dose, subsiding temporarily with medication. After receiving a booster dose, the patient experienced worsening polyarthritis affecting multiple joints including knees, elbows, wrists, shoulders, and neck, along with low-grade fever, fatigue, and functional decline. Despite outpatient anti-inflammatory therapy, symptoms persisted and worsened over the next six months, prompting hospitalization. Workup revealed elevated inflammatory markers (ESR 77 mm/hr, CRP 193.2 mg/L), synovial fluid consistent with inflammatory arthritis, and infectious serologies. Imaging showed joint effusions and calcified pulmonary granulomas. He was diagnosed with vaccine-induced reactive arthritis. Treatment with intravenous corticosteroids led to partial symptom relief, and he was discharged on oral steroids and initiated on methotrexate for long-term management. Conclusion: Clinicians should maintain a high index of suspicion for autoimmune phenomena such as reactive polyarthritis following COVID-19 vaccination, especially in patients with new-onset joint symptoms. Early recognition and referral to rheumatology may improve outcomes. Further studies are needed to clarify the pathophysiology, risk factors, and long-term prognosis of such vaccine-associated autoimmune conditions.