Effect of influenza vaccination in solid organ transplant recipients: A nationwide population-based cohort study.

Vaccination can prevent influenza in solid organ transplant (SOT) recipients. Using a modified season-specific approach over nine consecutive influenza seasons, we investigated influenza vaccination coverage and effectiveness in a population-based nationwide cohort study that included all SOT recipients aged ≥18 years who were living in Denmark from December 1, 2007 to April 1, 2016. The primary outcome was the season-specific risk of all-cause pneumonia admission. Secondary outcomes were season-specific influenza-related admission, intensive care unit (ICU) admission, and all-cause mortality. Crude and adjusted hazard ratios (aHRs) with 95% confidence intervals (CIs) were estimated using Cox proportional hazards regression models. In total, 11 381 person-years of follow-up data were collected from 5745 SOT recipients, 48% of whom were vaccinated. Influenza vaccination was associated with a reduced risk of all-cause pneumonia admission (aHR, 0.83; 95% CI, 0.69-0.99; p = .035) and all-cause mortality (aHR, 0.60; 95% CI, 0.47-0.76; p = .001), but not influenza-related admission (aHR, 0.75; 95% CI, 0.46-1.22; p = .24) or ICU admission (aHR, 0.84; 95% CI, 0.67-1.06; p = .14) during the same season. Despite these benefits, uptake of influenza vaccination among SOT recipients was low. Therefore, annual influenza vaccination needs to be prioritized.