Give an overview.
A local subacute type III hypersensitivity reaction.
Typically caused by vaccination against tetanus and/or diphtheria.
Describe the pathophyisology.
Intradermal antigen injection in a presensitized individual (previously exposed to the antigen, with preformed, antigen-specific IgG in the serum) → formation of antigen-antibody complexes in the skin → complement activation → local inflammation and possibly necrosis
List clinical features.
Cutaneous small-vessel vasculitis 
Localized swelling, erythema, hemorrhage
Occasional superficial skin necrosis a few hours after booster vaccination
The reaction typically peaks after 12–36 hours.
Injection site reaction unrelated to hypersensitivity
Shoulder injury related to vaccine administration
Increased tetanus and diphtheria antibody levels in the serum support the diagnosis.
Consider skin biopsy to rule out differential diagnoses.