Attitudes toward Vaccination for Pandemic H1N1 and Seasonal Influenza in Patients with Hematologic Malignancies

Despite the annual development of effective influenza vaccines, influenza remains a significant cause of morbidity and mortality in Canada. In the 2009–2010 influenza season, approximately 40,000 Canadians were infected with seasonal influenza or the pandemic H1N1 influenza virus,¹ and influenza has been estimated to cause 4,000–8,000 deaths in Canada each year.² It is estimated that a severe influenza pandemic could result in a 1% reduction in annual gross domestic product in Canada.³

Patients with hematologic malignancies are known to be at increased risk of influenza and its complications, with estimated mortality rates in the range 5%–27%.^{[4], [5], [6], [7] and [8]} Evidence for the efficacy of the influenza vaccine is limited and contradictory, and many assume that immunocompromised patients will not be able to generate a protective antibody response. Nonetheless, current evidence favors vaccination.⁹ Pollyea et al¹⁰ reported that eight of 15 trials on the efficacy of vaccination in patients with hematologic malignancies concluded that vaccination was beneficial. Both the Centers for Disease Control and Prevention (CDC) and the Public Health Agency of Canada (PHAC) advised that all immunocompromised patients, including those with cancer, receive both the seasonal influenza vaccine and the pandemic H1N1 influenza vaccine in the 2009–2010 influenza season.^{[11] and [12]}

Despite these recommendations, rates of influenza vaccination remain low for the general population and cancer patients in Canada, with rates reported at 40% and 65% respectively.^{[13] and [14]} A recent study by Yee et al¹⁵ reported similarly low influenza vaccination rates of 58% in cancer patients in the United States. Vaccination has long been a controversial public health issue, and many people choose not to be vaccinated due to fears that vaccines may not be safe and effective.^{[16], [17] and [18]} Lack of physician recommendation has also been cited as a significant factor in the decision to decline vaccination.¹⁶

In this study, we sought to determine what percentage of patients being treated for hematologic malignancies in an Ontario, Canada, cancer center received the H1N1 pandemic influenza vaccine in the 2009–2010 influenza season and to explore the barriers to vaccination in this high-risk population. We also collected information on the percentage of patients who received the seasonal influenza vaccine. It was general practice for physicians at this center to recommend influenza vaccination in accordance with the PHAC recommendations.

Methods

Patients being treated for hematologic malignancies at the London Regional Cancer Program (London, Canada) were invited to complete a survey regarding influenza vaccination (Appendix). The London Regional Cancer Program is a tertiary care center providing specialized cancer care to a population base of 1.2 million in southwestern Ontario. The survey was administered to patients eligible to participate in another study assessing antibody levels pre- and postvaccination with the H1N1 pandemic vaccine. Eligible patients were 18 years or older and being treated or followed for hematological malignancies at the London Regional Cancer Program who attended an appointment between October 28 and November 19, 2009, and returned for a follow-up visit between January 5 and March 26, 2010 (n = 151). Patients were asked if they had received the pandemic H1N1 influenza vaccine and the seasonal influenza vaccine during the 2009–2010 influenza season. Those who had declined vaccination were asked to describe the reasons for their choice. The survey provided a list of six possible reasons for declining vaccination and gave patients the option of writing in their own responses.

The results of the study were analyzed using InStat 3 software (GraphPad, La Jolla, CA). The Mann-Whitney U-test was used to compare continuous variables, and Fisher's exact test was used to compare proportions. The study was approved by the University of Western Ontario's Institutional Research Ethics Board (IRB 16627E).

Results

Of the 151 patients invited to participate, 129 completed the survey, yielding a response rate of 85%. Patient characteristics are shown in Table 1. The respondents ranged in age from 19 to 86 years, 56% were male and 44% were female, and patients aged 65 years or older comprised 52% of the study population. The mean age of the patient group was 62.7 ± 14.8 years. Overall 119 patients (92%) had received chemotherapy at some time during their illness, with 96 patients (76%) actively receiving chemotherapy, defined as treatment within the past 3 months. Diagnoses included acute leukemia, chronic lymphocytic leukemia, chronic myeloid leukemia, lymphoma, multiple myeloma, myelodysplastic syndromes, and myeloproliferative neoplasms.