CHMP5 and COVID-19: Of interest, IgG4 can be produced in repeated allergic exposure [257,258], and some anti-Spike IgE antibodies were characterized during a SARS-CoV-2 infection, especially in severe forms of COVID-19 [259]. Interestingly, this IgG4 production was detected following SARS-CoV-2 infection and after administration of anti-COVID-19 products, perfectly suggesting both the allergenic and tolerogenic side of the Spike protein and, thus, the production of this type of antibody by repeated exposure to this viral component [260-263].