Vaccine Effectiveness Against Influenza-Associated Hospitalizations in Adults with Liver Disease

Background. Influenza causes 100,000–710,000 hospitalizations annually in the U.S. Patients with liver disease are at higher risk of severe outcomes following influenza infection. This study evaluated vaccine effectiveness (VE) against influenza-associated hospitalization among adults with liver disease. Methods. Data from the U.S. Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN), a test-negative case-control study, from 2015 to 2020 was used to estimate VE among adults ≥18 years admitted for acute respiratory illness (ARI). VE was calculated as (1-adjusted odds ratio)*100%, comparing the odds of vaccine receipt between laboratory-confirmed influenza cases and test-negative controls using a multivariable logistic regression model with inverse probability of treatment weighting (IPTW). The model was adjusted for age, sex, race/ethnicity, study site, presence of immunocompromising condition, date of illness onset, days from illness onset to specimen collection, presence of liver disease, and the interaction between liver disease and vaccination. Results. In total, 1,622 (12.8%) of 12,704 adults hospitalized for ARI had ≥1 liver disease(s). Compared with those without liver disease, adults with liver disease were more likely to be admitted to the ICU (15.7% vs 12.8%, P = .001) or to die in hospital (3.0% vs 1.4%, P < .001). The IPTW-adjusted VE against influenza-associated hospitalization was 27% (95% confidence interval [CI], 22–32%) among patients without liver disease, but the VE of 11% (95% CI, -8–26) was not significant among those with liver disease. Significant effect modification of VE by the presence of liver disease was found (P < .05 for interaction term between liver disease and vaccination). Conclusion. While influenza vaccination significantly reduced the risk of influenza-associated hospitalization among adults without liver disease, the protective effect was not significant among those with liver disease. Further studies are warranted to evaluate influenza VE in patients with different types of liver disease and other methods to protect these vulnerable patients from ARI-related hospitalization. Our study underscores the public health importance of optimizing the influenza immunization strategy for patients living with liver disease.