Pneumococcal conjugate bacterial vaccines (PCVs) can prevent invasive disease caused byStreptococcus pneumoniae in healthy infants up to 24 months of age, according to a meta-analysis published in the June issue of Pediatrics.
To a smaller extent, the Italian research team reports, these vaccinations also reduce the incidence of acute otitis media and pneumonia.
To provide an up-to-date summary of the efficacy of pneumococcal vaccines (primarily 7-valent vaccine), Dr. Italo F. Angelillo, at Second University of Naples, and associates conducted a systematic bibliographic search of the medical literature published between 2000 and 2008 through electronic databases and manual searches of bibliographies of retrieved trials and review articles.
Included were prospective, randomized controlled trials comparing PCVs with placebo or control vaccines given as a primary series of 3 or 4 doses before 12 months of age. Of 370 citations identified, 49 articles were retrieved and reviewed, and 9 were selected on the basis of fulfilling all inclusion criteria.
The pooled data included close to 148,000 healthy infants up to 24 months of age, with study sizes ranging from 856 to 39,836 infants. Six trials used the 7-valent PCV (PCV-7), two used PCV-9, and one used PCV-11. Documented outcomes included invasive disease caused by S. pneumoniae in six trials, acute otitis media in five, and pneumonia in three. All but one trial reported both intention-to-treat and per-protocol analyses.
PCV was effective in reducing invasive pneumococcal disease involving vaccine serotypes by 89% in both the intention-to-treat and in the per-protocol analyses. It ranged from 74% in the intention-to-treat analysis to 63% in the per-protocol analysis for all serotypes.
For acute otitis media, efficacy for vaccine serotypes was 55% to 57%, while efficacy for all serotypes was 29%.
The efficacy of the vaccine in preventing pneumonia diagnosed by clinical examination alone was 6% to 7%, whereas the efficacy in preventing radiograph-confirmed pneumonia was 29% to 32%.
"The results are robust and consistent," Dr. Angelillo and associates maintain. Furthermore, "funnel plots did not show any significant asymmetry in studies that explored the effectiveness of PCV in the prevention of invasive pneumococcal disease and acute otitis media caused by vaccine serotypes, thus reducing the potential for publication bias."
Although the benefits in preventing otitis media or pneumonia were less striking compared with the effects in preventing invasive pneumococcal disease, the authors note that "considering the high burden of these diseases in infants, even a low efficacy has potential for tremendous impact on the health of infants in developing and industrialized countries."
Despite the "robust results," Dr. Angelillo's team noted problems with reporting, such as failure to provide detailed descriptions of patient sources or clear cross-referencing when multiple reports included some of the same patients. Also, they found a lack of information on whether the trial participants were truly representative or just a convenience sample of consecutive patients.
"These problems could be limited if journals refused to publish articles that do not specify the dates of data collection or give the absolute number of patients who were potentially available for recruitment."
Despite these shortcomings, the Italian researchers conclude, "The findings of this meta-analysis offer a global estimate of overall response to PCV in healthy infants."
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