Flu Vaccine May Cut Pneumonia Hospitalization Risk in Half

Tara Haelle

October 07, 2015

Vaccinations for influenza cut the risk for hospitalization for pneumonia approximately in half, according to a prospective case control study published online October 5 in JAMA.

"By performing systematic influenza testing for all patients with pneumonia, the study relied on an unbiased sample of laboratory-confirmed influenza-pneumonia hospitalizations," write Carlos G. Grijalva, MD, MPH, from the Department of Health Policy, Vanderbilt University School of Medicine, Nashville, Tennessee, and colleagues. Addressing shortcomings of previous research, the study also prospectively identified patients with pneumonia, restricted their analysis to influenza seasons, and included only patients with verified vaccination status, they write.

"The benefits of influenza vaccines are not restricted to prevention of fever and respiratory symptoms," Dr Grijalva told Medscape Medical News. "Influenza vaccines are also effective in preventing hospitalization for influenza pneumonia, which is a serious complication of influenza infections. It is especially important to understand these benefits now that we have influenza vaccines available and we are preparing for the upcoming influenza season."

The researchers analyzed data from the Etiology of Pneumonia in the Community study, a prospective, observational multicenter study that ran from January 2010 through June 2012 at four US sites. Dr Grijalva's team compared the influenza vaccination status of patients with pneumonia who were aged 6 months and older and who had laboratory-confirmed influenza with the status of patients with community-acquired pneumonia.

They controlled for demographics, smoking status, family composition, comorbidities, season, study site, and disease onset timing. They excluded patients with recent hospitalization, severe immunosuppression, or transfer from chronic care residential facilities. The groups were generally similar, except the patients with influenza were more likely to be black, and control patients had a higher prevalence of congenital heart disease and heart failure.

Among 2767 patients hospitalized for pneumonia, 5.9% (n = 162) had influenza, and 29% (n = 794) had received the current season's influenza vaccine. Among the 2605 control patients, 29% (n = 766) had received the vaccine compared with 17% (n = 28) of the cases. Dr Grijalva's team estimated the vaccine effectiveness at 56.7% (95% confidence interval [CI], 31.9% - 72.5%), with an adjusted odds ratio of 0.43 (95% CI, 0.28 - 0.68) for odds of cases' prior vaccination odds with odds of controls' vaccination.

"This means that about 57% of hospitalizations due to influenza-associated pneumonia could be prevented through vaccination," Dr Grijalva told Medscape Medical News. "Both children and adults benefited from influenza vaccination."

Among 68 children with influenza, 10% (n = 7) had been vaccinated compared with 29% (n = 376) of 1309 control patients (adjusted odds ratio [aOR], 0.25; 95% CI, 0.11 - 0.58). For children aged 6 months to 4 years, 8% of 40 cases had received the vaccine compared with 31% of 850 control patients (aOR, 0.16; 95% CI, 0.05 - 0.53), yielding an estimated 82% vaccine effectiveness in this age group. Among adults, 22% of cases and 30% of controls had been vaccinated (aOR, 0.59; 95% CI, 0.34 - 1.02).

"In separate assessments, the odds ratio of vaccination between cases and controls was 0.40 (95% CI, 0.19-0.87) for influenza A(H1N1)pdm09, 0.55 (95% CI, 0.28-1.09) for influenza A(H3N2), and 0.28 (95% CI, 0.09-0.83) for influenza B," the authors report.

"Findings from subgroup analyses suggest that the odds ratio of prior influenza vaccination between cases and controls was higher in patients with immunosuppressive conditions, including cancers and HIV infection, suggesting lower vaccine effectiveness," they also write.

Mark Schleiss, MD, a pediatric infectious disease physician at the University of Minnesota in Minneapolis, called the results "intuitive" but confirmed in a rigorous, multisite study. The use of multiple centers and a large number of participants make the findings "robust," he told Medscape Medical News.

"This is a reliable approach and analyzes the issue of influenza vaccine's effectiveness from a somewhat different but clinically very relevant perspective," Dr Schleiss said. "The noninfluenza pneumonia group serves as a valuable control and strengthens the findings. This confirms what we know: that influenza has a big impact on pneumonia, including secondary bacterial pneumonias."

He noted this study adds to the body of knowledge about the vaccine's benefits.

"It reminds us that the benefits of flu immunization extend far beyond just preventing the influenza viral infection, but extend, as this study shows, to pneumonia," Dr Schleiss said. "The protection is not perfect, and we need better vaccines. But even a fair-to-good vaccine is always going to be better than no vaccine at all."

The research was funded by the Influenza Division in the National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention. Dr Grijalva and several coauthors report receiving grants, support, consultancy fees, or data and safety monitoring committee work from one or more of the following companies: Pfizer, BioFire Diagnostics, Antimicrobial Therapy, American Foundation for Pharmaceutical Education, GlaxoSmithKline, Cubist Pharmaceuticals, Vertex, Visterra, bioMérieux, Roche, MedImmune, AbbVie, Novartis, Affinium Pharmaceuticals, Astute Medical, Crucell Holland, BRAHMS, Pfizer, Rapid Pathogen Screening, Venaxis and Cempra Pharmaceuticals, and CareFusion. One coauthors has a patent pending (13/632,874, Sterile Blood Culture Collection System). Dr Schleiss has disclosed no relevant financial relationships.

JAMA. Published online October 5, 2015. Full text

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