Why or how would someone have an allergic reaction to a booster shot?



For example: I received my first Moderna vaccine and did not have an immediate reaction. I did get very sick and develop and rash a week later. Yesterday, I received my second vaccine and within twelve minutes started having an allergic reaction. My entire body was on fire and my throat and tongue were swelling. They used an epipen and sent me to the hospital.

What happened between the first dose and the second dose? Why would the body react so differently? It was absolutely terrifying. No one has been able explain why I didn’t have a reaction the first time.

In: Biology

Two pieces to this one.

First, vaccine ingredients. In addition to the actual viral part of the vaccine, there are other things in there (not like crazy conspiracy theory nonsense, but like things that basically help extend the shelf life, increase effectiveness, etc.). An example is that the flu shot uses egg byproducts that people absolutely can be allergic to.

Second, allergic reactions vary in severity each time (and in my experience tend to be worse each time). You can also develope an allergy as time goes on. My guess would be you were already allergic to one of the ingredients in this drug, you got off relatively light with the first shot, and are getting a full blown allergic reaction on the second (maybe even because some amount of the first is still in your system and so you’re getting even more).

Not a doctor, but it sounds like an allergic reaction. You didn’t react to the first dose because you weren’t sensitive to it yet. Some people become allergic to certain substances over time with more exposure. Some never become sensitive, no matter the amount they are exposed to.

It’s not uncommon for your body to react more strongly to something after repeat exposures. It’s not exactly the same, but that’s also sort of what’s happening when you get repeated doses of a vaccine: your immune response to the disease gets stronger (although the allergic reaction is a different kind of reaction).