 Typically, the cells live for multiple decades, but there is variation in the longevity of these cells depending on the type of vaccine they were stimulated with and vaccine dosage.The reason for the differences in the longevity of memory B cells is currently unknown.However, it has been proposed that the differences in memory B cell longevity are due to the speed at which a pathogen infects the body and, accordingly, the number and type of cells involved in the immune response to the pathogen in the vaccine.