Factors associated to repeated influenza vaccination in the Portuguese adults with chronic conditions

Annual influenza vaccination is recommended to people with chronic conditions. This study aimed to estimate the proportion of chronically ill adults vaccinated against influenza in consecutive seasons and to identify associated factors. We used data from the first National Health Examination Survey (INSEF), a cross-sectional study conducted in 2015 on a probabilistic sample of individuals aged 25–74 years. The population was restricted to individuals who self-reported diabetes, a respiratory, cardiovascular, liver or kidney disease. Self-reported vaccination in 4 consecutive seasons was categorized in 3 levels: unvaccinated, occasionally (vaccinated 1–3 seasons) and repeatedly vaccinated (in all 4 seasons). A multinomial logistic regression was applied to estimate odds-ratio (OR) of influenza vaccination according to sociodemographic factors, chronic condition, health care use and status. In the target population, the 2014/15 influenza vaccine coverage was 33.8% (95% CI: 29.8–38.1). The higher coverage was found in individuals reporting renal disease (66.7%) and diabetes (43.8%). The coverage decreased to 32.6%, 26.0% and 20.8% for individuals with respiratory, cardiovascular and liver diseases, respectively. The probability of being repeatedly vaccinated, compared to unvaccinated, was higher in males (OR = 2.14: 95% CI: 1.31–3.52); aged 65 and 74 (OR = 4.39; 95% CI: 1.99–9.69); whom had an appointment with a general practitioner (OR = 2.77; 95% CI: 1.00–7.66) or other physician (OR = 3.95: 95% CI: 2.53–6.16); with no smoking habits (OR = 1.58; 95% I: 1.02–2.46) and reporting diabetes (OR = 2.13; 95% CI: 1.02–4.45). Finally, having a self-reported cardiovascular condition decreased the likelihood of being occasionally (OR = 0.38; 95% CI = 0.22–0.65) vaccinated against influenza. Younger individuals, females and the ones with a self-reported cardiovascular condition were identified as more likely of non-compliance to the vaccine uptake recommendation. Future vaccination strategies should focus on the previous identified population subgroups. Also, the medical recommendation of the influenza vaccine uptake should continue and be reinforced particularly in individuals with a cardiovascular condition.