Quantifying the waning of humoral immunity

Immunological memory is a defining feature of immunity, and a quantitative description of how it wanes would help better understand the processes underlying its maintenance and estimate the duration of protection after immunization. We analyzed the waning of antibodies to a panel of virus and vaccine antigens and found that a power-law model captured both the initial rapid decline and much slower subsequent waning. Importantly, accounting for the time post-immunization at which the waning was estimated reduced the difference between estimates for the rate of antibody waning to toxoid/protein vaccines and to live attenuated viruses. We found that protective levels of antibodies may be maintained for longer than previously estimated using exponential models fitted to data from the first decade following immunization. Our analyses indicate that the slow waning of antibodies over a time span of decades may be estimated from data from a shorter time frame of 2 to 3 years following immunization and stresses the importance of taking into account the time post-immunization at which antibody waning is estimated.