Background: Individuals with cardiopulmonary and other chronic conditions are at increased risk for severe complications of influenza. Few studies have examined influenza vaccine effectiveness (VE) in high-risk groups. We evaluated VE against influenza-associated hospitalization among adults with specific high-risk conditions.
Methods: Adults hospitalized with acute respiratory illness (ARI) during the 2015-16 influenza season were enrolled at eight hospitals participating in the US Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN) study. Respiratory specimens were tested for influenza by reverse transcription PCR. Measures of illness severity, underlying health status, and vaccination were obtained from medical records and enrollment interviews. Presence of high-risk conditions was determined from clinical codes assigned to prior year medical encounters. We estimated VE using a test-negative design as (1-adjusted odds ratio), comparing odds of PCR-confirmed influenza among vaccinated patients versus unvaccinated controls. Multivariate logistic regression was adjusted for age, sex, and other factors, stratifying by chronic conditions.
Results: Of 1467 adults hospitalized with ARI, 236 (16%) had PCR-confirmed influenza; 180 (78%) were A(H1N1)pdm09. In all, 1358 (93%) had ≥1 high-risk medical condition, and 1026 (70%) had ≥3 conditions. Cardiovascular (n=835), metabolic (including diabetes) (n=773) and lung conditions (n=692) were most common (Figure). Patients with ≥1 high-risk conditions were more likely to be vaccinated (70%) vs. patients not at high risk (31%, p <.001). Among all patients, VE against any influenza-associated hospitalization was 50% (95% CI: 31-63). VE was similarly high among patients with neurologic (VE=64%, 95% CI: 26-83), metabolic (VE=55%, 95% CI: 30-71), and cardiovascular (VE=53%, 95% CI: 27-69) conditions, though lower for patients with immunosuppression and malignancy (VE=20%, 95% CI: -42-54).
Conclusion: Vaccination significantly reduced risk of influenza hospitalization among adults with the most prevalent high-risk cardiovascular, metabolic, and lung conditions. Results support the benefit of vaccinating adults with existing specific chronic conditions.
E. T. Martin, None
A. S. Monto, None
D. Middleton, None
F. P. Silveira, None
R. Zimmerman, None
H. K. Talbot, Sanofi Pasteur: Investigator , Research grant . Gilead: Investigator , Research grant . MedImmune: Investigator , Research grant . Vaxinnate: Safety Board , none . Seqirus: Safety Board , none .
J. M. Ferdinands, None