Among elderly persons who have been
revaccinated, significant antibody responses
to most serotypes studied are generally
observed [3]. However, the magnitude
of the antibody response in some
studies has been lower than after initial
vaccination, raising questions about
whether these adults may experience hyporesponsiveness
or immune tolerance
to repeated doses of these polysaccharide
antigens [7]. Furthermore, few previous
studies have assessed the duration of the
immune response following revaccination.
In one recently published study de-signed to assess the dose response to 7-
valent pneumococcal polysaccharideprotein
conjugate vaccine (PCV7) in 220
elderly persons previously vaccinated
with PPSV23, among the participants
who received PPSV23 (ie, those who were
revaccinated with PPSV23), immunoglobulin
(Ig) G antibody levels were significantly
higher 1 month after revaccination
for the serotypes tested but decreased
toward the baseline after 1 year.
Functional antibody activity levels—
which are thought to be as important, if
not even more important, in predicting
clinical protection against pneumococcal
disease—were also significantly higher 1
month after revaccination versus prevaccination
levels but were not assessed
thereafter. Longer-term assessments of
the immune response were not conducted
[8].