My wife and I are in our late 70's and took our first vaccine (Moderna) on New Years Eve and have had no ill effects from the shot. Next day or so our arm was just a little sore but that is all.
Our daughter in law had taken the Moderna Vaccine shot about a week before we took the shot and she had a delayed allergic reaction after several weeks, injection site red and irritated, pain and itching and slight swelling and the doctor told her to take Benedryl and Tylenol and not to take the second Moderna shot. She is just fine now.

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James
On the Llano Estacado