Reasons for non-vaccination against influenza among older adults with hypertension in Brazil: a cross-sectional study

ABSTRACT The aim of this study was to estimate the prevalence of non-vaccination against influenza among Brazilian older adults with systemic arterial hypertension and determine the main reasons for non-adherence. A cross-sectional study was conducted using data from older adults (≥ 60 years of age) with hypertension who participated in the 2013 National Health Survey and reported not having been vaccinated against flu over the previous 12 months (n = 1,295). The analyses were performed using the Stata 14.0 software. The data were weighted because of the sampling design. An estimated 3,026,080 older adults with hypertension had not received a flu vaccine over the 12 months prior to the survey (22.6%). No significant associations were found with sex, age group or schooling. The prevalence of unvaccinated older adults was lower in the southern and southeastern regions of Brazil than in the northern and northeastern regions, even after adjusting for age. The prevalence was higher among individuals without private health insurance. The main reasons for non-vaccination were fear of a reaction, rarely having the flu and not believing in the protection of the vaccine. The present findings underscore the need for healthcare professionals to explain to the population the benefits of the vaccine for preventing severe influenza (protective effect and possible reactions) and for secondary prevention of cardiovascular events. Increasing the prevalence of vaccination in older adults with hypertension and other cardiovascular diseases is of fundamental importance within the realm of public health as a strategy for reducing occurrences of complications and deaths associated with influenza.


INTRODUCTION
Systemic arterial hypertension is a major risk factor for other cardiovascular diseases 1 and is highly prevalent in both adults and elderly people. 2,3 Data from the Brazilian National Health Survey revealed rates of 44.4%, 52.7% and 55.0% among Brazilian elderly people aged 60-64, 65-74 and ≥ 75 years, respectively, 4 and the prevalence increased with age (71.7% of individuals aged ≥ 70 years had high blood pressure or reported taking antihypertensive medication). 3 Individuals with cardiovascular disease are at greater risk of complications from influenza. 5,6 Besides the risk factors described in the literature (hypertension, obesity, physical inactivity, smoking, etc.), influenza contributes to cardiovascular morbidity and mortality. 6 The American Heart Association and American College of Cardiology indicate the flu vaccine for individuals with atherosclerotic disease. 7 The United Kingdom National Clinical Guideline Centre 8 and the Brazilian Cardiology Society 9 indicate the vaccine for individuals with heart failure.
Studies have shown that in individuals with cardiovascular disease, the flu vaccine reduces occurrences of cardiovascular events and mortality. 6,10 Among individuals with hypertension, vaccination prior to the flu season has been significantly associated with reduction of the risk of death due to acute myocardial infarction, stroke and all causes. 10 In Brazil, the flu vaccine is offered through the public healthcare system to groups that are at risk (elderly people and individuals with chronic respiratory, heart, neurological, liver, kidney and metabolic diseases), as a strategy for prevention of the disease, its severe forms and complications. 11 Higher rates of vaccination among individuals with hypertension have been observed since these campaigns began. 12,13 Since hypertension is a chronic disease that requires follow-up and treatment, most older adults in Brazil are dependent on the public healthcare system 14 and primary care is the main source of antihypertensive medications. 15 Thus, it can be hypothesized that this group is more attentive to information on vaccination campaigns and other offers from public healthcare services. However, after two decades of vaccine campaigns, approximately 20% of elderly people with hypertension are not receiving the vaccine, and this percentage has remained stable over the years. 12,16

OBJECTIVE
The aim of the present study was to estimate the prevalence of non-vaccination against influenza among older Brazilians with hypertension and determine the main reasons for non-adherence.

METHODS
A cross-sectional study was conducted using public domain data on elderly people (≥ 60 years) who participated in the 2013 National Health Survey, 17 reported having hypertension (n = 5,524) and reported having not been vaccinated against influenza over the previous 12 months (n = 1,295). We estimated the absolute number and proportion of non-vaccinated elderly people with hypertension and the respective 95% confidence intervals, according to sociodemographic characteristics, and determined the reasons for non-vaccination.
All estimates were made using the Stata 14.0 software and took the sampling design into consideration. The National Health Survey had received approval from the National Ethics Committee of the Health Ministry (certificate number: 328.159; June 26, 2013).
The prevalence of non-vaccination among elderly people with hypertension was lower than the rates found for elderly people in general and for those who reported not having hypertension (27.4% and 31.9%, respectively).

DISCUSSION
In the present study, the prevalence of vaccination against influenza among elderly people with hypertension was lower than what was expected for the general population of elderly people, given that the goal in 2013 was to vaccinate at least 80% of all individuals ≥ 60 years of age. 11 Considering the greater contact of this group with healthcare services, 12,15 the absolute number of unvaccinated individuals was high.
Previous studies also found that there were no associations between the vaccination rate and sex, 12,16,18,19 age group 18 or schooling. 18,19 Sato et al. 19 found that the chance of having been vaccinated was greater among elderly people registered with the Family Health Program. The reasons for non-vaccination given by these elderly people with hypertension were similar to those found for the older population in general. 18,19 Fear of side effects falsely attributed to the vaccine, not considering it important and having insufficient information regarding the benefits were the main reasons given. 12,21 Counseling by healthcare professionals has been positively associated with vaccination and should be used as a strategy for improving knowledge among elderly people regarding both the disease and the vaccine.

CONCLUSION
The main reasons for non-vaccination (fear of a reaction, belief that influenza is a rare event, belief that the vaccine does not offer protection and fear of needles) accounted for more than 60% of the reasons given by these elderly people. These findings underscore the need for