Is it bad, is it good, or is IgG4 just misunderstood?

Abstract

Repeated doses of mRNA vaccines for COVID-19 result in increased proportions of anti-spike antibodies of the IgG4 subclass, which are known to neutralize well and to form mixed immune complexes with IgG1 but, in a pure form, might be less effective than IgG1 or IgG3 antibodies in facilitating opsonization by phagocytes, complement fixation, and NK cell–dependent elimination of infected cells (see related Research Article by Irrgang et al.).