A case series of bacillus Calmette-Guérin scar reactivation after administration of both mRNA and viral vector COVID-19 vaccines.

Aim: Reactivation of the scar resulting from intradermal injection of bacillus Calmette-Guérin (BCG) is a common specific reaction in Kawasaki's disease. It has also sporadically been associated with viral infections, multisystem inflammatory syndrome in children, influenza vaccination and mRNA COVID-19 vaccination. In this case series, characteristics of BCG scar reactivation after different COVID-19 vaccinations are presented and possible mechanisms are discussed.

Methods: Data were collected from the spontaneous reporting system of the Netherlands Pharmacovigilance Centre Lareb. Descriptives were made for the case reports in which a BCG scar reactivation was detected.

Results: Since the start of the COVID-19 vaccination campaign in January 2021, the Netherlands Pharmacovigilance Centre Lareb has received 22 case reports of BCG reactivation after vaccination with a COVID-19 vaccine. In 20 case reports, it concerned mRNA COVID-19 vaccines Moderna (14) and Pfizer (6). In two case reports, the viral vector COVID-19 vaccine AstraZeneca was administered. Erythema and pain were the most frequently reported symptoms and the size of the inflammation was between 1.5 and 5 cm. BCG scar reactivation occurred with a median time to onset of 2 days after the second or booster COVID-19 vaccination, whereas the median time to onset was 7 days after the first COVID-19 vaccination. None of the BCG scar reactivations were treated.

Conclusions: The exact mechanism of the occurrence of BCG scar reactivation remains unknown, but involvement of heat shock protein 65 is suggested. BCG scar reactivation is a nonserious, self-limiting reaction that can occur after vaccination with both mRNA and viral vector COVID-19 vaccines.