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Reaction to COVID-19 vaccine at prior BCG site. My fiancee received the Bacille Calmette-Guérin (BCG) vaccine as an infant in Mexico, which protects against tuberculosis and leaves a scar as shown. 1/4
The day after receiving the Moderna vaccine she developed a circular redness and itching at the BCG scar (representative photo shown) which self resolved in a couple of hours. Of note it was in the same arm as the vaccine but not at the injection site. 2/4
Interestingly 6 days later the localized circular redness and itching RETURNED at the site of the BCG scar. There were NO concerning features such as difficulty breathing. I gave her Benadryl and the symptoms resolved. I found one similar case online. 3/4 https://www.aaaai.org/ask-the-expert/delayreac
In sum, if you have a BCG scar then redness & itching at the site of the BCG scar is a possible rare HARMLESS side effect from the Moderna vaccine. We're thankful to be vaccinated. Get your vaccine as soon as possible. 
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Of note, some people are having this same delayed hypersensitivity reaction in the arm that received the COVID vaccine, who do NOT have the BCG vaccine. It's harmless and improves with antihistamines. It's possible the BCG scar has no relevance.
