"Here, we report on the analysis of two independent cohorts of vaccinated health care workers, who developed an increase in anti-spike IgG4 antibodies and IgG4-switched memory B cells 5 to 7 months after the second mRNA immunization with Comirnaty."

https://www.science.org/doi/10.1126/sciimmunol.ade2798?adobe_mc=MCMID%3D49580958977069939882498092457145355506%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1675955042