Hypersensitivity to the Moderna COVID-19 vaccine caused by tromethamine: PEG is not always the culprit excipient

Abstract

Vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are considered the cornerstone of the solution to the current global pandemic. The first vaccines to receive authorization for emergency use in humans were the BNT162b2 Pfizer-BioNTech and the mRNA-1273 Moderna vaccines. Both contain synthetic mRNA that codes for the SARS-CoV-2 spike (S) protein, which is encased in a lipid nanoparticle envelope. Anaphylaxis and immediate hypersensitivity reactions were noted in only 1 case during phase III trials for BNT162b2, while no immediate hypersensitivity reactions were noted for the mRNA-1273 vaccine. However, a history of hypersensitivity to any component of the vaccines was an exclusion criterion. Nonetheless, cases of anaphylaxis were reported shortly after initiation of the vaccination campaign.