Exponential decline, ceiling effect, downregulation, and T-cell response in immunoglobulin G antibody levels after messenger RNA vaccine boosters: a case report

Ceiling effect or downregulation of peak immunoglobulin G levels was clearly observed after messenger RNA booster vaccination. After peaking, the IgG level declined exponentially, and the rate of decay decreased with each subsequent booster. Although this was a single-case study, this data may provide a generalized mathematical decay model for humoral immunity in healthy older adults. Moreover, our study provides insights into the immunogenicity after booster vaccination with messenger RNA vaccines.