Flu vaccinations cut risk of pneumonia hospitalizations by almost 60%, study finds

October 10, 2013

Study results were based on laboratory-confirmed hospital cases of pneumonia with and without influenza, in 2,320 children and adults. Many previous studies lacked either laboratory confirmation or vaccine status.

Influenza vaccination can reduce the risk of influenza-associated pneumonia hospitalizations by more than half, according to data presented at the recent IDWeek Meeting in San Francisco.

Using a case test-negative study design, Carlos G. Grijalva, MD, MPH, of Vanderbilt University School of Medicine, Nashville, Tenn., and researchers found that influenza vaccination was associated with a 59% reduction in the risk of laboratory-confirmed, influenza-associated pneumonia hospitalizations.

“The vaccine effectiveness appeared to be higher among children than among adults,” said Grijalva, assistant professor of health policy, preventive medicine, division of pharmacoepidemiology, department of health policy. “Several studies have shown that influenza vaccines can prevent acute respiratory diseases associated with influenza infections, but evidence of protection against other more severe outcomes, such as hospitalizations for influenza-associated pneumonia, is limited.”

The study

The finding comes from the CDC's Etiology of Pneumonia in the Community (EPIC) study covering two flu seasons - 2010 to 2011 and 2011 to 2012 - and part of a third, 2009 to 2010, in the cities of Memphis, Nashville, Chicago, and Salt Lake City.

The influenza vaccine effectiveness study included 2,320 children and adults hospitalized with pneumonia and enrolled in the EPIC study. The analyses compared influenza vaccination between patients hospitalized with laboratory-confirmed influenza pneumonia and patients hospitalized with pneumonia who tested negative for influenza.

Vaccination information for the study was verified through review of medical records, vaccination registries, and information from other providers (e.g., pharmacies).

Among study subjects, 130 had laboratory-confirmed influenza, Grijalva said. He and colleagues used regression analyses to determine the adjusted odds ratio (aOR) for influenza vaccination more than 14 days before disease onset in cases compared with non-cases. From that, they calculated vaccine efficacy as 1-aOR.

Of the 130 cases, 22% had influenza vaccination for the current season, compared with 35% of the non-cases. That yielded a vaccine efficacy of 59%, which did not vary substantially in sensitivity analyses, although there was some variation in subgroups. In particular, vaccine effectiveness was 79% in children but only 36% in adults.

“Most previous studies on this subject focused on all-cause pneumonia as the outcome but lacked laboratory confirmation of influenza infections, and several studies lacked verification of the vaccination status,” Grijalva said. “We designed this study to determine whether influenza vaccination reduced the risk of laboratory-confirmed, influenza-associated pneumonia hospitalizations in individuals ≥6 months of age with verified influenza vaccination information.”

Currently, the Advisory Committee on Immunization Practices recommends influenza vaccination for all eligible individuals six months of age or older. “Our study provides additional support to these recommendations, indicating that influenza vaccination can provide protection against influenza-related pneumonia hospitalizations,” Grijalva said.