Serum sickness (SS) and SS-like reaction (SSLR) are rare immune complex-mediated hypersensitivity illnesses characterised by key features of fever, rash, polyarthralgia or polyarthritis. They are self-limiting with an excellent prognosis, settling as the antigen is cleared. We describe a 30-year-old man who presented with fever, rash, polyarthralgia and subcutaneous soft tissue swelling in his hands and feet at day 5 after influenza vaccination. A thorough investigation for infective and autoimmune causes for the presenting symptoms was negative. Given the temporal relationship between the symptoms and influenza vaccination, clinical evidence and biological plausibility of influenza vaccination causing SSLR, a clinical diagnosis of SSLR was made. The patient was treated with anti-histamines, non-steroidal anti-inflammatories and glucocorticoids with gradual resolution of symptoms over 5 weeks.
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