Immune-related Adverse Events in Patients With Cancer Receiving Influenza Vaccination and Immune Checkpoint Inhibitors.

To the Editor—With interest, we read the study by Chong et al [1] who reported that 20% of patients with cancer who received influenza vaccination concurrently with immune checkpoint inhibitors (ICIs) experienced immune-related adverse events (IRAEs). Their findings were comparable to the rates reported in historical studies and are relatively similar to the rate that we determined in our retrospective analysis (26%) [2]. However, this rate of 20% was not obtained by directly comparing patients from the same prospectively included cohort as we did. The use of historical controls complicates the interpretation of their data, since historical controls receiving ICIs may have received influenza vaccine as well, considering the vaccination coverage of 45–56% among patients with cancer in the United States [3, 4].

In addition, we question the duration of the period of follow-up for IRAEs after influenza vaccination (median, 1.4 years) considering the relatively low immunogenicity of antigens included in the influenza vaccine. The active immune response following influenza vaccination has already waned after a few months and hemagglutination-inhibition titers do not reliably persist year-round in older adults but regress to prevaccination levels in 360 days [5].

Nevertheless, both studies confirm that influenza vaccination during administration of ICIs is safe and that the reported high overall rate of IRAEs (12 of 23, 52%) in the study by Läubli et al [6] with fewer subjects may have been a chance finding. Therefore, seasonal influenza vaccination can still be advocated in patients with cancer receiving ICIs.