Studies show pneumococcal vaccines' protection varies

Pneumonia chest x-ray
Pneumonia chest x-ray

scott feldstein / Flickr cc

Three new reports, including a population study in Africa and two meta-analyses, suggest that pneumococcal vaccines provide moderate protection against invasive pneumococcal pneumonia in children and adults but only limited protection against all-cause pneumonia.

Gambian children benefited

In the population study, reported in The Lancet Infectious Diseases, a large team of authors examined the effects of the introduction of pneumococcal conjugate vaccines (PCVs) in the tiny West African country of Gambia. The seven-valent vaccine (PCV7) was introduced there in August 2009, followed by PCV13 in May 2011. Most of the authors are with Gambia's Medical Research Council.

The investigators identified invasive pneumococcal disease (IPD) cases in the Upper River Region from 2008 to 2014, and compared IPD incidence during a baseline period of May 12, 2008, to May 11, 2010, and a 2-year period (2013 and 2014) after the introduction of PCV13.

They counted 320 IPD cases among 14,650 patients, of which 243 cases (75%) were in children under 5 years old. After PCV13 arrived, they determined, IPD decreased by 55% (95% confidence interval [CI], 30%-71%) in children 2 to 23 months old, mainly because of an 82% drop in serotypes covered by the vaccine. In children 2 through 4 years old, IPD incidence declined 56% (95% CI, 25%-75%), with a 68% reduction in PCV13 serotypes.

"Low-income and middle-income countries that introduce PCV13 can expect substantial reductions in invasive pneumococcal disease," the authors concluded.

Little effectiveness against CAP

In one of the two meta-analyses, published in Vaccine, three researchers from Montreal's McGill University sifted studies of the effectiveness of the 23-valent polysaccharide pneumococcal vaccine (PPV23) in preventing IPD and community-acquired pneumonia (CAP) in adults 50 years and older.

They found that the vaccine was 50% effective (95% CI, 21%-69%) against IPD in cohort studies and 54% (95% CI, 32%-69%) in case-control studies. But the vaccine showed little effectiveness against CAP: 4% in trials, 17% in cohort studies, and 7% in case-control studies, none of which percentages were statistically significant.

The authors said these findings were consistent with those of other systematic reviews. "The results suggest that the current practice of vaccinating the adults 65 years of age and older with PPV23 would have similar benefits to PCV13 in preventing potential cases of all-serotype IPD and all-cause CAP," they wrote.

'Weak protection' against all-cause pneumonia

In the other meta-analysis, also published in Vaccine, researchers in Beijing examined randomized trials that tested the efficacy of PPV23 for preventing all-cause CAP in adults. They included seven trials involving a total of 150,010 participants.

"High-quality evidence" revealed, they said, that the vaccine reduced the risk of CAP in adults by 13% (relative risk [RR], 0.87; 95% CI, 0.76-0.98; P = .11). The protection level looked slightly higher in the target population, consisting of adults 65 and older and younger adults at high risk for pneumonia: RR, 0.72; 95% CI, 0.69 -0.94; P = .58).

The researchers also noted signs of protection against pneumococcal pneumonia (RR, 0.54; 95% CI, 0.18-1.65; P = .01) and death from pneumonia (RR, 0.67; 95% CI, 0.43-1.04; P = .67), but these numbers didn't achieve significance, they said, possibly because of the small number of trials included.

"PPV-23 provided weak protection against all-cause pneumonia in an immunocompetent population, especially among the target population," the team concluded. "The additional benefit of PPV-23 in preventing CAP further supports its application in the target population."

See also:

Feb 17 Lancet Infect Dis study

Feb 17 Vaccine abstract of study by Canadian team

Feb 17 Vaccine abstract of study by Chinese team

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