“Methods: We conducted a 6-month longitudinal prospective study involving vaccinated health care workers who were tested monthly for the presence of anti-spike IgG and neutralizing antibodies. Linear mixed models were used to assess the dynamics of antibody levels and to determine predictors of antibody levels at 6 months.
Results: The study included 4868 participants, with 3808 being included in the linear mixed-model analyses. The level of IgG antibodies decreased at a consistent rate, whereas the neutralizing antibody level decreased rapidly for the first 3 months with a relatively slow decrease thereafter…
Conclusions: Six months after receipt of the second dose of the BNT162b2 [Pfizer] vaccine, humoral [immune] response was substantially decreased, especially among men, among persons 65 years of age or older, and among persons with immunosuppression.”