Seasonal influenza disease can be particularly severe in older people, but conventional trivalent and quadrivalent inactivated influenza vaccines can be ineffective in this age group when influenza A(H3N2) strains predominate. New enhanced trivalent vaccines are available and should be used in people aged 65 years and over.
- In Australia, the vast majority of cases of serious influenza disease and influenza-related deaths occur in adults aged 65 years and over; long-term sequelae that impact on activities of daily living are also common in this group.
- Standard influenza vaccines induce suboptimal antibody titres and show suboptimal levels of effectiveness in older adults. Two enhanced influenza vaccines are now available in Australia and should be used in older people; both have a good safety profile.
- During the 2019 influenza season in Australia, an adjuvanted trivalent vaccine that has been shown to provide enhanced protection in older adults is recommended and funded under the National Immunisation Program (NIP) for people aged 65 years and over.
- A high-dose version of the standard trivalent vaccine also provides enhanced protection in older people and is recommended for use in this group but is not funded under the NIP this year.
- The additional benefit of extra influenza B coverage and hence the need for a quadrivalent vaccine in older people has not been established. However, the benefit would be substantially less than the additional protection provided by enhanced vaccines.
- Influenza vaccine coverage in older people is about 75% each year; general practice staff are key partners in increasing this level of vaccination.
Illness due to influenza virus infection poses a severe burden on Australian healthcare systems. Globally, the WHO estimates that seasonal influenza causes three to five million cases of severe illness and 290,000 to 650,000 deaths annually.1 Influenza is a disease that affects both industrialised and developing countries. Although data from the developing world are limited, it is estimated that each year 99% of deaths in children under 5 years of age with influenza-related lower respiratory tract infections occur in developing countries.2 However, influenza more often results in severe disease in people with chronic underlying conditions and in older people and most influenza-associated mortality occurs in older adults.3
In 2017, the largest nonpandemic influenza season on record in Australia, more than 90% of the reported 1100 influenza- related deaths were in adults aged over 65 years.4 Much of the impact of influenza in older people is hidden and manifests as previously undetected underlying medical conditions or as a worsening of existing conditions, especially cardiovascular disease.5 For example, acute influenza can lead to decompensation in patients with congestive heart failure or diabetes mellitus and to an increased risk of myocardial infarction and stroke. As patients with these conditions are rarely tested for influenza, the burden of disease is greatly underestimated.6
Influenza can present differently in older adults, who often have a lower incidence of fever, more frequent lower respiratory symptoms such as cough, wheezing and chest pain, and atypical disease, with anorexia, mental status changes or unexplained fever as the only presenting symptoms.7,8 Patients with underlying chronic obstructive pulmonary disease (COPD) may experience worsening respiratory status. Heart failure may be an unrecognised complication. Pneumonia is a relatively common complication, especially in people with chronic cardiopulmonary disease.
Of great importance are recent data that show influenza causing hospitalisation negatively affects functional status in older people and leads to a decline in capacity for activities of daily living after the infection.9 As populations age, the occurrence of permanent disabilities due to influenza-related illness is increasing, causing major suffering and mandating the search for effective prevention programs.
There are two major influenza virus types that cause human illness, influenza A and B viruses, each with their own characteristics and effect on different community groups. Most severe human illness is due to influenza A viruses, further subdivided into A(H1N1) and A(H3N2) subtypes according to the two surface proteins haemagglutinin (H) and neuraminidase (N). Influenza A has its greatest impact on older adults and young infants, whereas influenza B is more likely to occur in the under 20 years age group.10