Safety of Inactivated Influenza Vaccine in Cancer Patients Receiving Immune Checkpoint Inhibitors (ICI).

Background. Cancer patients are at a higher risk for developing influenza (flu)- related complications. It is unclear if the flu vaccine exacerbates immune events in patients treated with immune checkpoint inhibitors (ICIs). Methods. We conducted an institutional review board-IRB-approved retrospective review of advanced cancer patients on ICIs who received the flu vaccine during three 3 consecutive seasons: 2014-2015, 2015-2016, and 2016-2017. The primary outcome assessed was any "new onset" immune-related adverse event (IRAE). A subset analysis of vaccinated patients newly treated with anti-programmed cell death protein 1 (PD-1) agents (nivolumab or pembrolizumab) was conducted to assess overall IRAE rates for comparison with published clinical trials. Results. During the three 3 seasons, 370 patients met criteria for ICI and vaccination within similar to twoapproximately 2 months (65 days). The most common underlying cancers were lung (46%) and melanoma (19%); 61% of patients received an anti-PD-1 agent only. In the entire cohort, 20% experienced an IRAE (any grade); incidence of grade 3 or 4 toxicity was 8%. No grade 5 events occurred. In the subset of 170 patients newly treated with anti-PD-1 agents, the overall IRAE rate was 18% and, grade 3/4 events occurred in 7.6%. Influenza was diagnosed in 2 patients. Conclusions. No increase in incidence or severity of IRAEs was detected in patients on ICIs who received the inactivated influenza vaccine within similar to approximately 2 months of ICI. For newly treated patients on anti-PDI-1 agents, IRAE rates were comparable to those from published clinical trials and did not vary with order of administration. Routine seasonal flu vaccination is encouraged in patients on ICIs.