Background Influenza may trigger complications, particularly in at-risk groups, potentially leading to hospitalization or death. However, due to lack of routine testing, influenza cases are infrequently coded with influenza-specific diagnosis. Statistical models using influenza activity as an explanatory variable can be used to estimate annual hospitalizations and deaths associated with influenza. Our study aimed to estimate the clinical and economic burden of severe influenza in Spain, considering such models. Methods The study comprised ten epidemic seasons (2008/2009–2017/2018) and used two approaches: (i) a direct method of estimating the seasonal influenza hospitalization, based on the number of National Health Service hospitalizations with influenza-specific International Classification of Diseases (ICD) codes (ICD-9: 487–488; ICD-10: J09-J11), as primary or secondary diagnosis; (ii) an indirect method of estimating excess hospitalizations and deaths using broader groups of ICD codes in time-series models, computed for six age groups and four groups of diagnoses: pneumonia or influenza (ICD-9: 480–488, 517.1; ICD-10: J09–J18), respiratory (ICD-9: 460–519; ICD-10: J00–J99), respiratory or cardiovascular (C&R, ICD-9: 390–459, 460–519; ICD-10: I00–I99, J00–J99), and all-cause. Means, excluding the H1N1pdm09 pandemic (2009/2010), are reported in this study. Results The mean number of hospitalizations with a diagnosis of influenza per season was 13,063, corresponding to 28.1 cases per 100,000 people. The mean direct annual cost of these hospitalizations was €45.7 million, of which 65.7% was generated by patients with comorbidities. Mean annual influenza-associated C&R hospitalizations were estimated at 34,894 (min: 16,546; max: 52,861), corresponding to 75.0 cases per 100,000 (95% confidence interval [CI]: 63.3–86.3) for all ages and 335.3 (95% CI: 293.2–377.5) in patients aged ≥ 65 years. We estimate 3.8 influenza-associated excess C&R hospitalizations for each hospitalization coded with an influenza-specific diagnosis in patients aged ≥ 65 years. The mean direct annual cost of the estimated excess C&R hospitalizations was €142.9 million for all ages and €115.9 million for patients aged ≥ 65 years. Mean annual influenza-associated all-cause mortality per 100,000 people was estimated at 27.7 for all ages. Conclusions Results suggest a relevant under-detected burden of influenza mostly in the elderly population, but not neglectable in younger people.

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Background Influenza is an acutely debilitating respiratory infection, contributing significantly to outpatient visits and hospitalizations. Spain lacks comprehensive and updated data on the burden of influenza, particularly in the outpatient setting. Our study aimed to fill this gap by estimating the clinical and economic burden of physician-diagnosed influenza cases in adults from four Spanish regions, stratified by age groups and presence of comorbidities. Methods A retrospective cost-of-illness study was conducted using data from an electronic medical records database from the National Healthcare Service (NHS) of four Spanish regions for individuals aged ≥ 18 years diagnosed for influenza during the 2017/2018 epidemic season. Health resource utilization and related cost data were collected, including primary care visits, referrals to other specialists, visits to the emergency department, hospitalizations, and prescribed medicines. Results The study reported a total of 28,381 patients aged ≥ 18 years diagnosed with influenza, corresponding to 1,804 cases per 100,000 population. Most patients were aged < 65 years: 60.5% (n = 17,166) aged 18–49 and 26.3% (n = 7,451) 50–64 years. A total of 39.2% (n = 11,132) of patients presented a comorbidity. Cardiovascular diseases were the most common comorbidity reported along with influenza. The mean healthcare cost per case was estimated at €235.1 in population aged 18–49 years, increasing by 1.7 and 4.9 times in those aged 50–64 (€402.0) and ≥ 65 (€1,149.0), respectively. The mean healthcare cost per case was 3.2 times higher in patients with comorbidities. The total healthcare cost of medically attended influenza cases was mainly driven by primary care (45.1%) and hospitalization (42.0%). Patients aged 18–64 years old accounted for 61.9% of the costs of medically attended influenza. Irrespective of age, patients with comorbidities accounted for 67.1% of costs. Conclusions Season 2017/2018 was associated with a considerable burden of influenza in Spain, which increased with age and presence of comorbidities. Individuals with comorbidities accounted for most of the costs of influenza. Results suggest that population aged 18–64 years old is generating the highest share of costs to the NHS when all healthcare costs are considered. Preventive strategies targeting subjects with comorbidities, regardless of age, should be warranted.

Adults aged 65 years or older suffer the most severe health effects of seasonal flu. Although the influenza vaccine is effective in preventing influenza virus infection and its complications, it is not as effective in the elderly due to age-associated immunosenescence phenomenon. Since 2009, a high-dose trivalent influenza vaccine has been approved in the United States for the immunization of people ≥ 65 years with an antigen concentration four times higher than the standard vaccine. Multiple clinical trials carried out over different seasons, and using different methodologies, have shown that the high-dose trivalent influenza vaccine is not only more effective, but it also has a similar safety profile and is more immunogenic than the standard dose vaccine in the prevention of flu and its complications in the elderly. This document reviews the current scientific evidence on the safety and immunogenicity of high-dose influenza vaccine in people aged 65 years and over, and includes information from randomized clinical trials, observational studies with data from real clinical practice, and systematic reviews, and meta-analysis.

Asbtract Background Electronic vaccine registries are not yet widely established. There is a need to real-time monitor influenza vaccine coverage, which may raise awareness to risk groups and professionals, and eventually allow to adopt tailored measures during the vaccination campaign. To evaluate the utility of the “Gripómetro”, a demographic study designed to monitor national and regional influenza vaccine coverage on a weekly basis in Spain. Methods Quantitative study based on surveys of the Spanish population between 18–80 years and a sample of primary care doctors and nurses randomly selected. Pre-proportional fixation has been established by Autonomous Communities and age group to guarantee the representativeness of all the autonomies. Results Interviews were conducted in 3400 households of general population and 807 respondents among health care professionals. We found that the results of influenza vaccination coverage in the population ≥ 65 years obtained by the Gripómetro for 2018–2019 season were mostly comparable with the official data presented by the Ministry of Health after the end of the vaccination campaign. Conclusions The Gripómetro is a robust research method that provides real-time data and trends for influenza vaccine coverage along with other useful information related to vaccination such as intention to vaccinate, motivation and barriers to vaccination.