Influenza Vaccination and Influenza-Associated Pneumonia

EBM Focus - Volume 10, Issue 41

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Reference - JAMA 2015 Oct 13;314(14):1488 (level 2 [mid-level] evidence)

  • Influenza vaccination reduced the risk of hospitalization due to influenza-associated pneumonia by about 50%.
  • In subgroup analyses, the vaccine was most effective in children, patients who were not immunocompromised, and patients without chronic disease.

Annual influenza vaccination is recommended for all persons ≥ 6 months of age, optimally before seasonal influenza activity begins in the community. The highest risk groups for influenza-associated complications include young children, adults over 50 years old, persons with chronic disorders, pregnant women, and immunocompromised patients, and these groups, and household contacts and caregivers, are especially encouraged to receive seasonal vaccination. In addition, healthcare personnel are also considered a high priority for vaccination (MMWR Recomm Rep 2013 Sep 20;62(RR-07):1). Previous studies have shown that influenza vaccination can reduce influenza illness and hospitalizations (BMC Med 2013 Jun 25;11:153, Cochrane Database Syst Rev 2014 Mar 13;(3):CD001269). However, the ability of influenza vaccines to specifically prevent hospitalizations for influenza-associated community-acquired pneumonia has not been well studied. In a recent nested case-control study from the Etiology of Pneumonia in the Community study, 2,767 adults and children > 6 months old hospitalized with community-acquired pneumonia during 3 influenza seasons and with verified influenza vaccine status were assessed for influenza infection. Patients with recent hospitalizations, severe immunocompromise, or incomplete vaccination status, and/or those residing in chronic care facilities were excluded.

Laboratory-confirmed influenza virus infection was found in 162 patients (5.9%), while the remaining 2,605 patients were influenza negative. Overall, 28.7% were vaccinated with the current season influenza vaccine at least 14 days before they developed pneumonia. Comparing cases of influenza-associated pneumonia to influenza-negative controls, the rate of influenza vaccination was 17% vs. 29% (p < 0.001) and the estimated vaccine effectiveness for preventing pneumonia due to influenza was 56.7% (95% CI 31.9%-72.5%). In subgroup analyses, vaccine effectiveness was higher in children, patients who were not immunocompromised, and patients without chronic disease.

Community-acquired pneumonia is a major health concern, accounting for approximately 1 million hospitalizations in the United States in 2010 alone (National Hospital Discharge Survey 2010 PDF). Respiratory viruses are the most frequently detected pathogens in patients hospitalized with community-acquired pneumonia (N Engl J Med 2015 Jul 30;373(5):415), and they can increase susceptibility to secondary bacterial infections. In this study, influenza was detected in 6% of pneumonia cases, of whom 83% had not received their yearly influenza vaccination. Overall in the United States, only about 50% of persons aged ≥ 6 months receive annual influenza vaccinations, despite clear recommendations (MMWR Morb Mortal Wkly Rep 2014 Dec 12;63(49):1151). The results of this study suggest that patients who received the influenza vaccination decreased their risk of hospitalization due to influenza-associated pneumonia by more than half, a timely reminder in places where the season for flu vaccination has already begun.

For more information, see the Influenza vaccines in adults and Influenza vaccines in children topics in DynaMed Plus. DynaMed users click here and here.