The biggest fear in allergy shots is the severe, or even fatal, reaction.  Each year 3-4 people die from a severe allergic reaction to allergy shots.  The biggest risk seems to be poorly controlled asthma.  Epinephrine given immediately is the most important intervention.  The reaction can happen up to 30 minutes after the shot, however, the vast majority happen within 15 minutes.  If an epinephrine injection is given, the patient should be ready to need another treatment.  Biphasic reactions are common and can happen hours later.  Drawing a tryptase level and instituting steroids seems appropriate.  Interestingly, large local reactions do not clearly predict systemic reactions.  However, they may still require a dose reduction.