Rationale: Vaccination is the most effective protection against influenza. Patients with interstitial lung diseases (ILDs) represent a high-risk group for influenza complications. Thus, yearly influenza vaccination is recommended, but evidence on its effects is sparse. Objectives: This study aimed to compare all-cause mortality and all-cause and respiratory-related hospitalization between vaccinated and unvaccinated patients with ILD. Methods: Using data from the largest German statutory health insurance fund (about 27 million insurees in 2020), we analyzed four influenza seasons from 2014-2015 to 2017-2018 and compared vaccinated with unvaccinated patients with ILD. Starting from September 1 of each year, we matched vaccinated and unvaccinated patients in a 1:1 ratio using a rolling cohort design. Mortality and hospitalization were compared with Kaplan-Meier plots, and effects were calculated during the influenza season (in season) with risk ratios. Results: Both the vaccinated and the unvaccinated cohorts included 7,503 patients in 2014-2015, 10,318 in 2015-2016, 12,723 in 2016-2017, and 13,927 in 2017-2018. Vaccination rates were low at 43.2% in season 2014-2015 and decreased over time to 39.9% in season 2017-2018. The risk ratios for all-cause mortality were 0.79 (95% confidence interval [CI], 0.65-0.97; P = 0.02) in season 2014-2015, 0.66 (95% CI, 0.54-0.80; P < 0.001) in 2015-2016, 0.89 (95% CI, 0.76-1.04; P = 0.15) in 2016-2017, and 0.95 (95% CI, 0.81-1.12; P = 0.57) in 2017-2018. The effects on all-cause hospitalization and respiratory-related hospitalization were similar in all seasons. Conclusions: Although an unequivocally beneficial impact of influenza vaccination in patients with ILD could not be demonstrated, we observed promising results regarding avoidance of all-cause mortality in half of the seasons observed. Given the low vaccination rates, further efforts are necessary to improve vaccination rates in patients with ILD.
Keywords: Germany; administrative data; statutory health insurance; survival; vaccination rate.