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

AimReactivation 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.MethodsData 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.ResultsSince 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.ConclusionsThe 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.