In SARS, a type of “priming” of the immune system was observed during animal studies of SARS spike protein-based vaccines leading to increased morbidity and mortality in vaccinated animals who were subsequently exposed to wild SARS virus. The problem, highlighted in two studies, became obvious following post-vaccination challenge with the SARS virus . found that recombinant SARS spike-protein-based vaccines not only failed to provide protection from SARS-CoV infection, but also that the mice experienced increased immunopathology with eosinophilic infiltrates in their lungs. Similarly , found that ferrets previously vaccinated against SARS-CoV also developed a strong inflammatory response in liver tissue (hepatitis). Both studies suspected a “cellular immune response”.
structural characterization of the fusion core in syncytin envelope protein of human endogenous retrovirus family W. Rui Gong et al. Biochem Biophys Res Commun. 2005.
The vaccine being taken forward, BNT162b2, encodes an optimized version of the whole spike protein, which should lead to “more consistent responses across diverse populations and in older adults,”