> Class switch toward noninflammatory, spike-specific IgG4 antibodies after repeated SARS-CoV-2 mRNA vaccination https://www.science.org/doi/full/10.1126/sciimmunol.ade2798

This one was posted here at least once: https://news.ycombinator.com/item?id=34147802

One-sentence summary: IgG4 suppresses the immune response, stopping the body from fighting back, so you don't have allergic reactions to things like pollen and dust.