Burden of Influenza
Seasonal influenza is a major burden on public health worldwide causing up to one million deaths each year. Annually it is estimated that it attacks 5-10% of adults and 20-30% of children globally and causes significant levels of illness, hospitalization and death.
Seasonal influenza is a major economic burden. It can result in increased healthcare costs and workplace absences and reduced productivity. The World Health Organization cites studies from developed countries that suggest the total annual cost of influenza is between U$1 million to U$6 million per 100,000 population. Another report investigating the cost of flu in 2003 calculated U$10.4 billion annually in direct medical costs and U$16.3 billion in indirect costs associated with lost earnings and loss of life. From a societal perspective, the total economic burden of the flu in the United States is $87.1 billion. During influenza season it is estimated that influenza-like-illness is responsible for 45% of workdays lost and for 49% of low productivity days among working adults aged 50–64 years.
Vaccination is the most effective measure at preventing influenza and its severe outcomes. Recent studies show vaccine can reduce the risk of influenza by about 60% among the overall population during seasons when most characterized circulating influenza viruses are like the viruses included in the vaccine.6 When there is a good match between the vaccine antigens and the circulating viruses influenza vaccines offer approximately 70-90% protection against clinical disease in healthy adults.
Vaccination can reduce the economic burden caused by the disease. Studies have shown universal vaccination can produced substantial cost savings from individual and societal perspectives.
Seasonal influenza risk groups
A growing number of countries and international bodies recognize particular groups at higher risk from influenza.2,8 These include: the elderly (over 65), children, pregnant women, those with chronic disease and underlying health conditions and healthcare professionals.
The Elderly (over 65)
Burden – Studies indicate that nearly all influenza vaccination recommendations target older adults who are generally over 65 but can range from as low as 50. The elderly are known to suffer more frequently from serious morbidity and mortality due to influenza and it is suggested that low- and middle-income countries may have a higher mortality than in higher income countries. In addition, people aged ≥85 years were 16 times more likely to die from an influenza-related illness compared with persons aged 65 to 69 years.
Benefits –Influenza vaccination is known to reduce severe illness and complications. Influenza vaccination of the elderly not living in care may reduce the number of hospitalisations by 25-39% and overall mortality by 39-57% during influenza seasons3 Among nursing home residents, influenza vaccination can reduce hospitalizations (all causes) by about 50%, the risk of pneumonia by about 60% and the risk of death (all causes) by 68%.2,8 It should be noted however that vaccine effectiveness decreases with age.10 Annual influenza vaccination is recommended to ensure an optimal match between the vaccine and prevailing influenza strains, and because, unlike the long-lasting, strain-specific immunity following natural infection, influenza vaccines induce protection of relatively short duration, particularly in the elderly.
Economic benefits – Cost savings from vaccinating the elderly come from reducing hopsitalisations and death. Systematic reviews of cost–effectiveness analyses among elderly populations found influenza vaccination to be cost-effective or cost-saving.
Burden - Compared to non-elderly adults, children have higher rates of visits to doctors, hospitalisations and deaths due to influenza. It can lead to high rates of school absenteeism and lost days of work among parents and others in contact with children. There is a substantial burden associated with influenza in children less than 5 years of age. A recent study estimated that 90 million cases of influenza occurred among children lea than 5 years and 28,000-115,500 associated deaths. The burden greater in developing countries has been estimated to be as much as 15 times higher when compared to developed countries.
Benefits - Influenza vaccination helps reduce visits to doctors, hospitalisations and death to children. It also helps reduce the burden to the wider community. Studies have indicated that children are a source in the transmission of influenza in communities, households and sustain annual epidemics.
Economic Benefits - Economic evaluations of vaccinating children have generally found this strategy to be either cost-saving (i.e. costing less to perform than not to perform when taking into account all the costs of influenza and its complications) or cost-beneficial, especially when applied to a wider perspective (i.e. including productivity losses).
Burden – Pregnant women are at particular risk of severe complications and death from influenza and the risk is exacerbated by co-morbidities such as asthma, diabetes mellitus, and obesity, and late trimester pregnancy. The infection may also lead to complications such as stillbirth, neonatal death, pre-term delivery, and decreased birth weight.
Benefits – Maternal immunization against influenza not only protects the women but also prevents negative effects on fetal development due to maternal influenza infections and reduces rates of illness in infants for at least the first 6 months of life. Inactivated vaccines have been shown to be safe and effective in pregnant women and their offspring when given at any trimester.
Economic Benefits – It has been found that universal vaccination with inactivated trivalent influenza vaccine is cost-saving relative to providing supportive care alone in the pregnant population. In addition, in Canada, targeted vaccination of pregnant women with co-morbidities has been found to be cost-saving.
Those with chronic disease
Burden – This group includes those with cardiovascular, respiratory (asthma, chronic bronchitis and emphysema and other pulmonary diseases) pulmonary and metabolic diseases (such as diabetes mellitus), renal dysfunction, immune-suppressing conditions, chronic liver disease (especially with cirrhosis), neurodevelopmental disorders (cerebral palsy, musculodystrophy, cognitive disorders), morbid obesity and haematological diseases (sickle cell anemia, thalassemia major). This group are at higher risk from serious influenza, hospitalisation and death. Elevated risk is driven by age and severity of the condition amongst other factors.
Benefits - Vaccination reduces death, severe illness, complications and hospitalisations although immunocompromise groups do not respond as robustly to vaccines as healthy individuals.
Economic benefits - Studies looking at the economics of influenza vaccination of those with chronic disease indicate it is cost effective. Examples of these wide ranging studies include adult hemodialysis patients, asthma sufferers, and those with cardiovascular disease.
Burden – Health care workers are additional risk of being exposed to influenza compared to the general population. They risk passing on influenza to patients who are at increased risk of severe disease and may respond less well to vaccine. Transmission of influenza from HCW to patients was given as a principle source of infection for patients in a review of nosocomial influenza infection. Last, staff absences due to influenza can impact and disrupt health services.8 Vaccination rates of HCW remain low in many countries. A review on health care workers attitudes to influenza vaccination found lack of knowledge and lack of convenient access to the vaccine as the main reasons for lack of vaccine uptake.
Benefits – Vaccination not only protects health care workers and it also protects vulnerable patients. It also may reduce work absenteeism and consequent disruption to health services.
Economic benefits - Vaccination of health care workers has economic benefits. A Thai study found the cost of investigating an influenza outbreak in their intensive care ward was over 10-times that of vaccinating all of the staff.24 Another study found the economic benefits outweighed the costs by a factor of 4.5.
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Lee BY. et al. Cost-effectiveness of adjuvanted versus nonadjuvanted influenza vaccine in adult hemodialysis patients. Am J Kidney Dis. 2011 May;57(5):724-32.
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