Influenza Vaccination May Lower Risk of Influenza-Associated CAP Hospitalizations

Preliminary findings of a study presented in an oral abstract session during the October 2-6, 2013 IDWeek meeting suggested that influenza vaccination was associated with a reduced risk of influenza-associated community-acquired pneumonia (CAP) hospitalizations.

Carlos G. Grijalva, MD, MPH, lead study author, assistant professor of health policy-preventive medicine, Department of Health Policy, Division of Pharmacoepidemiology, Vanderbilt University, Nashville, TN, also revealed that influenza vaccination appears to be more effective in children than in adults for the prevention of this outcome.  

In an interview with Consultant360, Grijalva explained that, while several studies have demonstrated that influenza vaccination prevents acute respiratory infections associated with influenza, it remains unclear whether influenza vaccination reduces the risk of other, more severe outcomes, such as influenza-associated pneumonia. Most studies on this subject have focused on all-cause pneumonia as the outcome and lacked laboratory confirmation of influenza infections and verification of the participants’ vaccination status.

“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,” said Grijalva.

For their analysis, Grijalva and colleagues used data collected by the Centers for Disease Control and Prevention (CDC) EPIC (Etiology of Pneumonia in the Community) study, a prospective, multicenter study of the incidence and etiology of CAP hospitalizations in children and adults.

This study of influenza vaccine effectiveness included 2320 patients hospitalized with CAP and enrolled in the EPIC study at four study sites across the country during three consecutive influenza seasons (January 2010-June 2012).

Vaccine effectiveness was estimated by comparing the vaccination status between influenza-positive CAP cases and influenza-negative CAP controls using logistic regression models, controlling for demographics, season, site, high-risk conditions, and time from disease onset.Influenza vaccination was assessed by patient self-report and verified through record review, and influenza infection was confirmed by reverse transcriptase-polymerase chain reaction performed on nose/throat swabs.

Researchers found that 22% of the 130 patients with CAP who had laboratory-confirmed influenza had received the influenza vaccination, compared with 35% of the 2190 patients with CAP who did not have influenza.

The overall adjusted vaccine effectiveness was 59%, and stratified estimates were 79% in children and 36% in adults.

These results were consistent with the results from sensitivity analyses, which included restriction to complete influenza seasons, patients with CAP who were admitted within seven days of disease onset, and patients who were negative for influenza but positive for other respiratory viruses as controls.

When questioned about the limitations of their analysis, Grijalva acknowledged that “We were not able to verify the vaccination status for all participants in the study and, despite our efforts, it is possible that some residual confounding may remain after our statistical analyses were done.”

Grijalva pointed out that the Advisory Committee on Immunization Practices (ACIP) currently recommends influenza vaccination for all eligible subjects aged ≥6 months.

“Our study provides additional support to these recommendations indicating that influenza vaccination can provide protection against influenza-related pneumonia,” he said.

The EPIC study is funded by the CDC.

-Meredith Edwards White

Reference

Grijalva CG, Zhu Y, Williams DJ, et al. Prevention of laboratory-confirmed influenza pneumonia through vaccination: preliminary results from the CDC Etiology of Pneumonia in the Community (EPIC) study. Abstract presented at: IDWeek 2013; October 2-6, 2013; San Francisco, CA. Abstract 80. Available at: https://idsa.confex.com/idsa/2013/webprogram/Paper39870.html. Accessed October 9, 2013.