This case was reported in a literature article and described the occurrence of Sweet's syndrome in a 41-year-old male patient who received Influenza vaccine Quadrivalent unspecified season. On an unknown date, the patient received Influenza vaccine Quadrivalent unspecified season at an unknown dose. On an unknown date, 1 day after receiving Influenza vaccine Quadrivalent unspecified season, the patient experienced Sweet's syndrome (serious criteria GSK medically significant), painful rash, fever, arthralgia, erythropapular rash, skin plaque, epiderma spongiosis and edema. The patient was treated with triamcinolone, niacinamide and diclofenac. On an unknown date, the outcome of the Sweet's syndrome, painful rash, fever, erythropapular rash, skin plaque, epiderma spongiosis and edema were recovering/resolving and the outcome of the arthralgia was not recovered/not resolved. The reporter considered the Sweet's syndrome, painful rash, fever, arthralgia, erythropapular rash, skin plaque, epiderma spongiosis and edema to be related to Influenza vaccine Quadrivalent unspecified season. Additional information was provided. This case was reported in a literature article and described the occurrence of Sweet's syndrome in a 41-years old male patient who was vaccinated with unspecified influenza vaccine (manufacturer unknown). The patient was a man. The patient had no significant past medical history. No information on patient's family history or concurrent condition or concomitant medication was provided. On an unspecified date, the patient received unspecified influenza vaccine (administration route and site unspecified; dosages unknown; batch number not provided). Age of vaccination was not provided. On an unspecified date, 1 day after vaccination, the patient presented with a painful rash on his left neck and arm that persisted for several months. Review of systems was positive for occasional fevers and arthralgias. Physical examination revealed erythematous papules and plaques on the lateral neck and left arm. Laboratory and diagnostic Imaging Laboratory evaluation was negative. Specific studies included complete blood count (CBC), comprehensive metabolic panel, erythrocyte sedimentation rate (ESR), Anti-neutrophil cytoplasmic antibody, C-Reactive Protein, Creatine phosphokinase (CPK), C3, C4, Rheumatoid factor, Antinuclear antibody, anti-Extractable Nuclear Antigen, anti-Cyclic citrullinated peptide, anti-Double-stranded deoxyribonucleic acid, angiotensin converting enzyme, Venereal Disease Research Laboratory, and herpes simplex virus/varicella zoster virus, Chest x-ray was also negative. A punch biopsy from the neck demonstrated slight epidermal spongiosis with papillary dermal edema and a diffuse dermal neutrophilic infiltrate. No vasculitis was identified and direct immunofluorescence was negative. The patient was treated with triamcinolone cream, minocycline, and niacinamide. His cutaneous manifestations significantly improved, but his arthralgias were still present. Rheumatology subsequently started him on diclofenac. The author considered the event of Sweet's syndrome related to unspecified influenza vaccine. The authors stated "The pathogenesis of Sweet's syndrome remains unknown, but its association with underlying diseases suggests a hypersensitivity reaction. Sweet's syndrome is often divided into three general categories depending on the clinical setting: Classic, malignancy-associated, and drug-induced. The classic form is seen predominantly in middle-aged women and often preceded by an upper respiratory infection. Less common causes include gastrointestinal infection, pregnancy, and inflammatory diseases, most notably inflammatory bowel disease. Preceding vaccination has been rarely described as a cause of Sweet's syndrome. Only a few cases of influenza vaccine-induced Sweet's syndrome have been reported in the literature. The malignancy-associated form represents approximately 10-20% of vases. The most common cancers are hematologic malignancies, especially acute myelogenous leukemia. However, solid organ tumors have also been well documented. Sweet's syndrome can precede, follow, or appear concurrently with the associated malignancy. The drug-induced form of Sweet's syndrome can be due to a variety of culprits, although the strongest association exists with granulocyte-colony stimulating factor. Discontinuous of the offending drug results in rapid clearance, although medication rechallenge frequently leads to recurrence. Sweet's syndrome typically presents with painful, erythematous to violaceous papules, nodules or plaques. Pseudovesicular or pseudopustular lesions can also develop due to underlying dermal edema. Although classically involving the face, neck, upper extremities or trunk, lesions can present anywhere on the body. Fever is the most common systemic manifestation, but arthritis, arthralgia".