Allergic reaction and Immediate allergy

Allergic reaction noun - Hypersensitivity reaction to a particular allergen; symptoms can vary greatly in intensity.

Immediate allergy and allergic reaction are semantically related. In some cases you can replace phrase "Immediate allergy" with "Allergic reaction", this phrases are similar.

Immediate allergy noun - An allergic reaction that becomes apparent in a sensitized person only minutes after contact.

Allergic reaction and immediate allergy are semantically related. You can use "Allergic reaction" instead a noun phrase "Immediate allergy".