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Cochrane Database Syst Rev. 2003;(4):CD000422. |
Vaccines for preventing pneumococcal
infection in adults.
Dear K, Holden J, Andrews R, Tatham D.
National Centre for Epidemiology and Population Health, Australian National
University, Building 62, Canberra, ACT, Australia, 0200. keith.dear@anu.edu.au
BACKGROUND: Diseases caused by Streptococcus pneumoniae (S. pneumoniae)
continue to cause substantial morbidity and mortality throughout the world.
Polysaccharide pneumococcal vaccines have been developed for over 50 years and
may have the potential to prevent disease and death. OBJECTIVES: To assess the
effectiveness of polysaccharide pneumococcal vaccination in preventing disease
or death in adults. SEARCH STRATEGY: Trials were identified by electronic
searches of the Cochrane Central Register of Controlled Trials (CENTRAL) issue
2, 2003 (which includes the Cochrane ARI Group's specialised register); MEDLINE
(January 1966 to June 2003); and EMBASE (1974 to June 2003). We searched
existing literature. The bibliographies of all newly revealed studies were read
in order to identify further studies. The vaccine manufacturers, the lead
authors of newly identified studies not included in existing meta-analyses were
contacted. SELECTION CRITERIA: A) Prospective, randomised or quasi-randomised
studies comparing pneumococcal vaccines with placebo, control vaccines or no
intervention.B) Case-control studies (including indirect cohort studies)
assessing pneumococcal vaccine effectiveness against invasive pneumococcal
disease. Cohort studies are excluded. DATA COLLECTION AND ANALYSIS: A) Randomised
studies. Trial quality assessment was conducted by two reviewers (JH and DT).
Data extraction was done by three reviewers (JH, DT, KD). There were many
instances of unclear or incomplete data in the trial reports, and the final
dataset was arrived at after much deliberation and discussion, including
comparison with the data used in two previous reviews of this question. Due to
the age of the trials (dating back to 1954 in one case) it was not generally
possible to obtain clarification from the authors, though a partial
clarification was achieved in one case.B) Non-randomised studies. Study quality
was assessed by two reviewers (RA and KD). MAIN RESULTS: The combined results
from the randomised studies fail to show that the polysaccharide pneumococcal
vaccine is effective in preventing either pneumonia (outcome 6: odds ratio =
0.77, confidence interval 0.58, 1.02, number = 14) or death (outcome 8: odds
ratio 0.90, confidence interval 0.76, 1.07, number = 11). Despite encouraging
data from some very early trials, pooling trials published from 1977 on
suggests there is no effect (outcome 6; odds ratio = 0.96, confidence interval
0.80, 1.15, number = 12; outcome 9: odds ratio = 0.98, confidence interval
0.88, 1.09, number = 10). The available data cannot distinguish whether this
heterogeneity in results is due to improvements in trial methodology and
reporting, to differences in trial setting or to real loss of efficacy over
time. This is because the early, poorly reported trials were conducted in high-risk
healthy populations where the expected benefit is greatest.The case-control
studies show significant efficacy in preventing invasive pneumococcal disease:
OR 0.47 (CI 0.37, 0.59) corresponding to an efficacy of 53%. REVIEWER'S
CONCLUSIONS: While polysaccharide pneumococcal vaccines do not appear to reduce
the incidence of pneumonia or death in adults with or without chronic illness,
or in the elderly (55 years and above), the evidence from non-randomised
studies suggests that the vaccines are effective in the reducing the incidence
of the more specific outcome, invasive pneumococcal disease, among adults and
the immunocompetent elderly (55 years and above). Surveillance data suggest
that infection rates vary widely between and also within countries, but a
typical figure in developed countries is 0.01%, or 10 per 100,000 per year.
Efficacy of 50% then corresponds to a number-needed-to-treat (NNT) of 20,000
vaccinations per infection avoided, and perhaps 50,000 per death avoided.
Publication Types:
· Review
· Review, Academic