Safety and antibody response, including antibody persistence for 5 years, after primary vaccination or revaccination with pneumococcal polysaccharide vaccine in middle-aged and older adults.

Background: This study assessed antibody levels for 5 years after primary vaccination or revaccination with 23-valent pneumococcal polysaccharide vaccine (PN23).

Methods: Subjects were enrolled into 4 study groups by age (50-64 or > or = 65 years) and prior vaccination status (no prior vaccination or 1 vaccination 3-5 years previously). Blood was obtained on day 0 (before primary vaccination or revaccination), day 30, day 60, and annually during years 2-5.