Influenza vaccination reduced flu-related CAP hospitalizations in children, adults

October 4, 2013

SAN FRANCISCO — Influenza vaccination reduces the risk for influenza-associated pneumonia hospitalizations and seems to be more effective in children compared with adults in preventing this outcome, according to findings presented here during ID Week 2013.

Carlos G. Grijalva, MD, MPH, assistant professor of health policy, department of health policy (preventive medicine) division of pharmacoepidemiology at Vanderbilt University in Nashville, Tenn., said influenza vaccination was associated with an overall 59% reduction in the risk for influenza-associated hospitalizations for community-acquired pneumonia (CAP). However, vaccine effectiveness was 79% in children and 36% in adults in the prevention of pneumonia associated with influenza.

“These preliminary findings indicate influenza vaccination was associated with a 59% reduction in the risk of influenza-associated pneumonia hospitalizations,” Grijalva said during his presentation.

Grijalva and colleagues assessed the effectiveness of influenza vaccines in preventing influenza-associated CAP hospitalizations from January 2010 to June 2012 using data from the prospective CDC Etiology of Pneumonia in the Community (EPIC) study.

Patients hospitalized with CAP at study sites in Chicago, Memphis, Tenn., Nashville, Tenn., and Salt Lake City were enrolled during three consecutive influenza seasons. Influenza infections were identified by reverse transcriptase-polymerase chain reaction performed on nasopharyngeal and oropharyngeal samples. The study was restricted to patients aged at least 6 months, with verified vaccination and influenza infection status, who were enrolled during influenza seasons.

Grijalva said the investigators estimated vaccine effectiveness by comparing vaccination status between influenza-positive CAP cases and influenza-negative CAP controls using logistic regression models, controlling for demographics, high-risk conditions, season, site and time from disease onset. Sensitivity analyses included restriction to complete influenza seasons, CAP patients admitted within 7 and 14 days of disease onset, and patients who were influenza-negative but positive and negative for other respiratory viruses as controls.

A total of 2,320 CAP patients (45% of total enrolled in EPIC) were eligible for the vaccine effectiveness study. Of 130 influenza-positive CAP cases, 29 (22%) were vaccinated compared with 767 (35%) of 2,190 influenza-negative controls.

The overall adjusted vaccine effectiveness was 59% (95% CI, 49-66). Stratified estimates were 79% (95 CI, 61-89) for children and 36% (95% CI, 6-56) for adults. Results from sensitivity analyses were consistent with the main findings.