Influenza vaccination was not associated with an increased risk of developing immune-related adverse events (irAEs) in a real-world population of patients with cancer receiving pembrolizumab, according to results of a retrospective study published in JCO Oncology Practice.

Results of studies investigating the impact of influenza vaccination on the incidence of irAEs in patients with cancer treated with immune checkpoint inhibitors (ICIs) have been conflicting.

This retrospective study identified adult patients with cancer treated at the Mayo Clinic in Rochester, Minnesota, who received at least 1 dose of the programmed cell death-1 (PD-1) inhibitor pembrolizumab between September 2014 and August 2017. Corresponding demographic and clinical data were extracted from patient medical records.

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The main criterion for assigning patients to the influenza vaccinated group was receipt of the influenza vaccine within 30 days of starting pembrolizumab or during pembrolizumab therapy. All other patients were placed in the nonvaccinated group. The primary study endpoint was the incidence of irAEs in the vaccinated group compared with the nonvaccinated group.

Of the 162 patients included in the study, 70 and 92 patients were assigned to the vaccinated and nonvaccinated groups, respectively. The most common cancer diagnosis was melanoma (56.2%), followed by non-small cell lung cancer (13.6%). All patients had stage IV disease. The median patient age was older in the vaccinated group (68.6 years) compared with the nonvaccinated group (59.5 years; P =.002).

Interestingly, the frequency of any-grade irAEs was lower in the group who underwent influenza vaccination (25.7%) compared with the group not receiving the influenza vaccine (40.2%), although this difference was not statistically significant (P =.07). Similarly, those in the vaccinated group had a lower incidence of grade 3 or 4 irAEs compared with the nonvaccinated group (5.7% vs 13.0%), but this difference did not reach statistical significance (P =.2). However, the vaccinated group received a significantly higher median number of cycles of pembrolizumab compared with the nonvaccinated group (14 vs 9.5; P =.006).

Following multivariable analyses that adjusted for age, sex, cancer type, and number of cycles of pembrolizumab, influenza vaccination was found to be an independent predictor of lower irAE incidence (odds ratio [OR], 0.4; 95% CI, 0.2-0.9; P =.03).

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Limitations of these analyses identified by the study authors included the potential for bias resulting from patient self-selection, the lack of information regarding rationales for influenza nonvaccination, and the potential for differences in the reporting of symptoms across patients.

 “Our findings demonstrated no increase in irAEs associated with annual influenza vaccination in patients receiving an ICI and further support planned patient care quality initiatives to educate clinicians on influenza vaccination in the population of patients with cancer,” the study authors noted in their concluding remarks.


Failing JJ, Ho TP, Yadav S, et al. Safety of influenza vaccine in patients with cancer receiving pembrolizumab [published online February 6, 2020]. JCO Oncol Pract. doi: 10.1200/JOP.19.00495