Why are allergy shots given in both arms

Patient: Why are allergy shots given in both arms for some adults?I’ve been researching it and it explains the process very well except for why it’s injected in both arms rather than two shots in one.

Doctor: HelloThank you posting your query on “Ask the Doctor”Good QuestionThere are 2 vials (such as “LEFT” and “RIGHT”) “RIGHT”), there should be 2 injections each time. The vials with the lowest (smallest) numbers should be used first. Numbered vials are always given in sequence.Actually the logic is allergy shots may develop severe anaphylactic (adverse) reaction. If full dose is given it could be life threatening.Hence small unit is used first and patient is observed for 30 minutes for any adverse reaction and if no reaction is seen other shot is given.Hope this was helpful