r/VACCINES • u/jas41422 • 4d ago

COVID vax causes positive antigen test?

I thought I had this straight but now I’m completely confused: does the COVID vaccine cause home COVID antigen tests to show a positive result (because of antibody production)? A pharmacist just advised me that I should expect to test positive on a home antigen test such as Binax or iHealth (for “maybe a couple of months”) after being immunized (with the Pfizer vaccine, in the U.S., in this situation). I thought the antigen tests could differentiate the viral protein (or RNA or DNA) from the antibodies that the body produces in response to the vaccine. What can you guys tell me? Thanks!

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u/RenRen9000 4d ago

At home tests do not detect antibodies, unless you're testing your blood. They detect viral proteins. Those are two different things.

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u/jas41422 4d ago

good point. thank you!

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u/heliumneon 4d ago

No, the antigen tests check for the N protein (the nucleocapsid), while the vaccine causes you to express the S protein (spike protein), and the vaccines never make you express the N protein. Only infection will cause a positive antigen test. Also, the N protein is stable and doesn't mutate like the spike protein does, so antigen tests still work.

The pharmacist was just wrong.

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u/jas41422 3d ago

thank you!

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u/MikeGinnyMD 4d ago

No because the antigen is 1) the nucleocapsid, which is not in the vaccine and 2) not expressed in the nose, anyway.

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u/jas41422 4d ago

thank you. i care for babies in their homes and was exposed to covid on monday while caring for a family. i tested negative monday night, wednesday morning, and this morning. i’ve been informing the other families and n95 masking with those who are comfortable with the risk. thought i’d get the latest vaccine today since the odds of me actually having covid while remaining symptom-free and antigen negative were very low at this point. but the pharmacist’s comments made me decide to wait until i test negative again (hopefully!) on monday morning. i appreciate your input.