Search

BackgroundComirnaty, Pfizer-BioNTech’s polyethylene-glycol (PEG)-containing Covid-19 vaccine, can cause hypersensitivity reactions (HSRs) in a small fraction of immunized people which can, very rarely, culminate in life-threatening anaphylaxis. A role of anti-PEG antibodies (Abs) has been proposed, but causality has not yet been proven in an animal model. This study aimed to provide such evidence using anti-PEG hyperimmune pigs (i.e., pigs displaying very high levels of anti-PEG Abs). We also sought to find evidence for the role of complement (C) activation and thromboxane A2 (TXA2) release in blood as contributing effects to anaphylaxis.MethodsPigs (n=6) were immunized with 0.1 mg/kg PEGylated liposome (Doxebo) i.v. the rise of anti-PEG IgG and IgM was measured in serial blood samples with ELISA. After 2-3 weeks, during the height of seroconversion, the animals were injected i.v. with 1/3 human vaccine dose (HVD) of Comirnaty, and the hemodynamic (PAP, SAP), cardiopulmonary (HR, EtCO2,), hematological parameters (WBC, granulocyte, lymphocyte, and platelet counts) and blood immune mediators (anti-PEG IgM and IgG Abs, C3a and TXA2) were measured as endpoints of HSRs.ResultsA week after immunization of 6 pigs with Doxebo, the level of anti-PEG IgM and IgG rose 5-10-thousands-fold in all animals, and they all developed anaphylactic shock to i.v. injection of 1/3 HVD of Comirnaty. The reaction, starting within 1 min, led to the abrupt decline of SAP along with maximal pulmonary hypertension, decreased pulse pressure amplitude, tachycardia, granulo- and thrombocytopenia, and paralleling rises of plasma C3a and TXB2 levels. These vaccine effects were not observed in non-immunized pigs.ConclusionsConsistent with previous studies with PEGylated nano-liposomes, these data show a causal role of anti-PEG Abs in the anaphylaxis to Comirnaty. The reaction involves C activation, and, hence, it represents C activation-related pseudo-allergy (CARPA). The setup provides the first large-animal model for mRNA-vaccine-induced anaphylaxis in humans.