With increased age, people become more prone to all infections and produce fewer responses for vaccines. This is due to the lowered levels of function of immune systems against the infections.
With increased age, thymus atrophy and/or hyposecretion of hormones from thymus gland result in reduced activity of T cells against infections. Less number of T cells respond to infections.
The reduced T cell production also makes the B cells less responsive. Reduced responses of B cells towards infection results in slower immune response as antibody levels do not rise quickly.
