Erythema Multiforme Reactions Following Pfizer/BioNTech (Tozinameran) Vaccination: Two Case-Reports with Positive Rechallenge and Review of the Literature.

Aim: Pfizer/BioNTech (BNT162b2) is a COVID-19 vaccine with a reassuring safety profile. The main adverse reactions are mild local reactions. Cutaneous reactions are generally minor. The most common cutaneous reaction reported was a local injection-site reaction.

Case study: Here we present 2 cases of erythema multiform (EM) following BNT162b2 vaccination with positive rechallenge. The 1^st case was about a 51-year-old woman who developed 5 days after the 1st dose of the mRNA Pfizer/BioNTech (BNT162b2) a macular, erythematous, roundshaped lesions on the hands, knees and soles. She experienced a positive rechallenge one month later. In the 2^nd case, a 55-year-old man presented 6 days following the 2^nd shot of the mRNA Pfizer/ BioNTech (BNT162b2), targetoid eruption on the upper and lower members. The patient reported that he had the same skin lesions in ankles and soles few days following the 1^st shot of the same vaccine.

Conclusion: Few cases of EM following COVID-19 vaccination were reported in the literature and positive rechallenge in only one case. Rechallenge was not performed in most cases. Our two cases are particular because of the positive rechallenge in both patients. This is the gold standard to confirm that the vaccine was the culprit agent in inducing EM.