system
Given the following post, respond as if you're commenting on Reddit:
human
How does the immune response that causes hay fever differ from the immune response that is utilised by COVID vaccines? (And why don't antihistamines affect the latter?)

I always have a rough time aroung grass pollen season, and recently got the Moderna vaccine. I've been assured that taking my usual antihistamies won't have any effect on the vaccine working, and I believe that, but I'd love to know why.

Since allergies are an immune response, and antihistamines suppress them, what is different about other kinds of immune response that means antihistamines don't disrupt them?
gpt
The answer is in the word. Anti-histamine inhibits histamine (inflammatory protein) from being released by specific immune cells, mainly granulocytes (basophils, eosinophils, neutrophils). Vaccine immune response is focused more on lymphocyte specialization, sensitizing B-lymphocytes to antigens which then become plasma cells that produce antibodies to previously encountered antigens. Of course this is a very simplified explanation of immunology.