23-valent pneumococcal polysaccharide vaccine (PPV23) for the prevention of invasive pneumococcal diseases (IPDs) in the elderly: is it really effective?

INTRODUCTION: Incidence of invasive pneumococcal diseases (IPDs) in Italy is constantly increasing and that is particularly true among the elderly. 23-valent polysaccharide pneumococcal vaccine (PPV23) is recommended to this age group and offered in all Italian regions. However, efficacy of PPV23 on preventing IPDs is debated. We therefore performed a review of the most recent available meta-analyses in order to assess the efficacy of PPVs.
METHODS: The literature search was conducted using PubMed and Scopus search engines. We used the following keywords: "pneumococcal", "polysaccharide", "vaccine", "efficacy", "elderly", "meta analysis". Only meta-analyses published in the last 7 years were selected. We examined the results of the selected meta-analyses and assessed their quality according to the PRISMA recommendations.
RESULTS: The search returned 16 results in PubMed and 12 in Scopus: among them we selected 3 meta-analyses. According to our quality assessment, all meta-analyses showed generally positive results and almost all items of the PRISMA checklist were respected. However, the research protocol and the registration number were absent in all the 3 revisions and the flow-chart was not shown in Moberley's and Melegaro's works. In the study by Huss et al. the relative risk of developing IPDs among vaccinated subjects was 0.90 (95%CI: 0.46-1.77, I2 4.9%), indicating a very slight benefit after vaccination. This contrasts with the results of the Cochrane Review by Moberley et al., in which the PPVs showed a protective efficacy in reducing the risk of IPDs of 74% (OR 0.26, 95% CI: 0.15-0.46) with no statistical heterogeneity (I2 0%). Melegaro et al. found a reduction not statistically significant of the incidence of IPD of 65% (OR 0.35; 95% CI 0.08-1.49) among healthy elderly, while the global estimate of vaccine efficacy among high risk elderly was minimal (OR 0.80; 95% CI 0.22-2.88).
CONCLUSIONS: Most of the studies suggest that the PPVs confer low protection against IPDs. Anyhow, their methodological heterogeneity does not allow definitive conclusions. While waiting to see the results of new trials about the efficacy of PPVs, in particular of PPV23, and the extension of the use of conjugate vaccine among the population over 65, stakeholders should be aware of the results of the meta-analyses discussed in this paper during the implementation of the vaccination programs for the elderly in Public Health.