International guidelines recommend that annual influenza vaccination be performed in patients with idiopathic pulmonary fibrosis (IPF). Viral infections are recognized to be triggers of acute exacerbation (AE). The purpose of this study was to investigate the role of annual influenza vaccination on AE occurrence.

236 patients with incident IPF were included in the multicentric longitudinal prospective cohort COhorte FIbrose (COFI), and followed for 5 years. Influenza vaccination status was requested annually. We have defined aone-year vaccination coverage from September the first to August the 30th of the following year. 638 annual observations were available with an informed vaccination status. To evaluate the association between annual influenza vaccination and AE occurrence, two mixed-effect Cox regression was used. For the second model we divided patients in 3 groups:

– patients vaccinated every year;

– patients vaccinated at least half of the years of follow-up;

– patients vaccinated less than half the years of follow-up.

Only the first AE was considered. The definition of AE was that of Akira et al.

Mean follow-up was 33.2±23.6 months. 36 AEs occurred in 33 patients. Of the 33 patients, only 27 had an informed vaccination status in the year of their AE. Nine (33%) patients who experienced an AE weren’t vaccinated. For 141 (22%) annual observations, the patient didn’t receive the vaccine. In this model, influenza vaccination was associated with a decreased occurrence of AE but this did not reach the level of significance in this small population (HR:0.58 CI95%0.23-1.46, P=0.25). In the first group patients were vaccinated every year and consisted of hundred and thirty-three individuals. The second group was composed of patients vaccinated at least half of the years of follow-up, with 35 patients. And 36 patients were vaccinated less than half the years of follow-up in the last group. In the second model, patients vaccinated less than half the years of follow-up were significantly more at risk to present AE compared to patients who were vaccinated every year (HR:2.77 CI95%1.11-6.93, P=0.03).

In our IPF cohort, only about half of the patients had influenza vaccination coverage throughout the follow-up period. Annual influenza vaccination seems to reduce the risk of AE but due to a lack of power this association was not significant. However patients vaccinated less than half the years of follow-up were significantly more at risk to present AE compared to patients who were vaccinated every year. A study with a larger number of patients is highly desirable to confirm this association.