In a population-based study published in the Journal of Clinical Oncology, researchers found that the influenza vaccine protected patients with cancer against developing flu, supporting clinical practice guidelines recommending vaccination for cancer patients and survivors. However, its effectiveness appeared to vary according to cancer type, with patients with solid tumors deriving greater benefit than those with hematologic malignancies.
“Seasonal influenza vaccination is recommended for patients with cancer despite concerns of disease or treatment-associated immunosuppression, [but] the benefits … are uncertain,” Phillip S. Blanchette, MD, from the University of Western Ontario, and co-authors explained. In this observational study, Dr. Blanchette and investigators sought to strengthen the evidence regarding the importance of influenza vaccination.
The researchers first identified 26,463 adults who had been diagnosed with cancer and undergone influenza testing during the 2010-2011 to 2015-2016 influenza seasons in Ontario. Next, they linked data from an individual-level cancer registry, respiratory virus testing for influenza, and health administrative claims to determine vaccination status and outcome.
After influenza testing, patients were categorized as either influenza virus test-positive (cases) or test-negative (controls). The researchers then estimated vaccine effectiveness by comparing the ratio of the odds of vaccination among cases and controls.
Patients’ mean age was 70 years and the mean time since diagnosis was six years. The majority of patients (69%; n=18,205) had solid tumors, the most common of which were breast, lung, and prostate cancers. Approximately one-quarter of patients (23%; n=6,171) were receiving active chemotherapy during the influenza vaccination period.
A total of 4,320 patients (16%) tested positive for the influenza virus; 11,783 (45%) were vaccinated. Looking at patient characteristics between cases and controls and between vaccinated and unvaccinated people, the researchers observed that vaccinated patients were more likely to be older, have a solid tumor malignancy, not be receiving chemotherapy, and have more medical comorbidities.
After adjustment for age, sex, rurality, income, chemotherapy exposure, comorbidities, and influenza season, vaccine effectiveness against laboratory-confirmed influenza was 21%. Effectiveness against hospitalization for laboratory-confirmed influenza was similar, at 20%. However, the reductions in intensive care admissions for influenza and death within 30 days of specimen collection in inpatients were not statistically significant (TABLE).
Sex, timing between hospital admission and specimen collection, and location of specimen collection appeared to have no impact on vaccine effectiveness. However, age altered effectiveness: 33% for patients aged 18 to 65 years, compared with 15% in patients older than 65 (p=0.02).
Cancer type also led to variability in vaccine effectiveness: The benefit was only 5% in individuals with hematologic malignancies, compared with 25% in those with solid tumor malignancies (p=0.015). However, the researchers could not “determine the extent to which this difference was due to disease versus treatment-associated immunosuppression.”
Still, “no significant differences in vaccine effectiveness were observed according to active chemotherapy use, especially among patients with solid tumor malignancies,” the authors reported. “These results demonstrate vaccine effectiveness among patients with cancers and survivors, although [it was] somewhat lower than among the general population.”
Because the strongest vaccine effectiveness was observed in younger patients with solid tumor malignancies, “we need to increase the rate of seasonal vaccination among younger patients with cancer,” the authors concluded. “Nonetheless, our results also suggest a need to develop improved influenza vaccines for patients with cancer, especially among older patients and those with hematologic malignancies.”
The findings from this analysis are limited by the potential misclassification of vaccination status for patients vaccinated outside of physician offices or pharmacies. The study population also included patients with active cancer and people who had survived cancer, leading to substantial variability in vaccine effectiveness, depending on specific malignancy types and chemotherapy regimens. Data were acquired retrospectively, which may have introduced bias.
Blanchette PS, Chung H, Pritchard KI, et al. Influenza vaccine effectiveness among patients with cancer: a population-based study using health administrative and laboratory testing data from Ontario, Canada. J Clin Oncol. 2019;37:2795-804.