A study has examined the duration of protection given by vaccination and re-vaccination using the 23-valent polysaccharide pneumococcal vaccine (PPV) in people aged 50 and above.

In the first report, the authors note that there is some controversy over the degree of protection given by the 23-valent PPV in older people. They therefore examined response to primary vaccination and re-vaccination up to five years. Participants were adults aged 50 and over who were generally healthy and whose medical condition was stable. They were divided into four groups by age (50-64, and 65+), and by previous vaccination status. They then received the standard PPV or matching placebo in one arm, and one month later were crossed over and given the alternate preparation in the other arm. Blood was taken for assessment of IgG antibody to pneumococcal polysaccharide levels before the first injection, before the second injection, four weeks after the second injection, and then at yearly intervals. Outcome measure was IgG level to eight of the vaccine serotypes.

There were 1,008 people initially enrolled, of whom 964 completed the first 2 months observation. Baseline IgG levels were higher in the re-vaccination groups, with no significant difference by age. After both primary vaccination and re-vaccination, there were significant IgG rises in both age groups. The rise after re-vaccination was delayed, with slight falls at 30 and 60 days, however levels at subsequent time points were similar. For most serotypes, IgG levels subsequently remained above baseline for the five year assessment period.

The authors conclude that both primary vaccination and re-vaccination with the PPV induce antibody responses in people aged over 50 that persist for at least five years observation.

Results from the older subset are described specifically in an accompanying paper. These indicate that the response to both primary vaccination and re-vaccination were similar in participants aged 65 and over to those in younger people. The authors therefore conclude that re-vaccination with PPV in this age group gives comparable results to primary vaccination.