key: cord-0721389-gatw9r2q
authors: Lim, Darren Wan-Teck; Ng, Dorothy Hui Lin; Low, Jenny Guek-Hong
title: Bacillus Calmette–Guérin scar flare after an mRNA SARS-CoV-2 vaccine
date: 2021-08-03
journal: CMAJ
DOI: 10.1503/cmaj.210696
sha: 80785f884536bba15e755edd0c2383f15807a98e
doc_id: 721389
cord_uid: gatw9r2q

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A 34-year-old woman presented to our outpatient clinic with swelling and erythema over the site of her childhood Bacillus Calmette-Guérin (BCG) vaccination scar, 7 days after receiving her first dose of the BNT162b2 (Pfizer-BioNTech) messenger ribonucleic acid (mRNA) vaccine against SARS-CoV-2 on the ipsilateral arm ( Figure 1A ). She reported associated myalgia and fatigue. The BNT162b2 vaccination site was not inflamed. The second dose of vaccine was completed without incident.

A 45-year-old woman presented to our outpatient clinic with erythema and swelling of her BCG scar on the contralateral arm 4 days after receiving her second dose of the BNT162b2 mRNA vaccine ( Figure 1B) . The BNT162b2 vaccination site was not inflamed, and her second dose was completed without incident.

In both cases, the swelling and erythema of the BCG scar resolved spontaneously within 7 days, without further treatment.

Sporadic cases of BCG scar inflammation were recently reported after second doses of the mRNA-1273 (Moderna) and BNT162b2 mRNA vaccines, and they followed a similar clinical course to that of our patients. 1 The mechanism of inflammation is not known. We postulate that it could result from T cell bystander stimulation by vaccine-induced immune activation. Reactivation of the BCG scar has been described with influenza vaccination, childhood Kawasaki disease and viral infections; 2,3 hence it is possible that non-mRNA-based SARS-CoV-2 vaccines could lead to similar reactions. Immune crossreactivity of the lipid nanoparticles in mRNA-based vaccines against the lipid-rich mycobacterial cell wall is plausible, although we are not aware of data to suggest that such molecu lar mimicry occurs.

This phenomenon is likely to be under-reported. However, BCG scar flares after vaccination with current mRNA vaccines against SARS-CoV-2 appear to be benign, as in the cases presented here, and should not alarm physicians, limit vaccinations, nor be a reason for vaccine hesitancy.

BCG scar local skin inflammation as a novel reaction following mRNA COVID-19 vaccines in two international healthcare workers

Erythema at the bacillus Calmette-Guerin scar after influenza vaccination

Human herpes virus type 6 can cause skin lesions at the BCG inoculation site similar to Kawasaki disease

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