High-dose influenza vaccine
The high-dose trivalent influenza vaccine contains 60 mcg haemagglutinin per strain, instead of 15 mcg, and produces a dose-dependent increase in antibody response. Several studies have shown that it induces higher immune responses in older adults, with improved efficacy in clinical trials against influenza infection compared with the standard trivalent influenza vaccine. The high-dose vaccine also shows improved efficacy in clinical trials.21,22 Although high-dose influenza vaccine is recommended as a preferred vaccine for use in older people, it is not funded under the NIP in 2019.
Benefit of enhanced vaccines.
The attributable additional benefit of using an enhanced vaccine will vary from year to year depending on the predominant circulating strain (H3N2 or not) and the degree of match with the vaccine strains. However, in several real-life effectiveness studies in older people, enhanced vaccines have shown on average about 25% extra protection against disease and even higher additional protection against severe disease.20 Given the burden of disease associated with influenza in older people, this additional protection has enormous implications. During the severe 2013-14 influenza season in the US, the Centers for Disease Control and Prevention estimated that each 5% increase in vaccine effectiveness saved 86,000 hospitalisations in that year.
Safety of enhanced vaccines
In the two decades since the adjuvanted trivalent influenza vaccine was licensed, it has established a good safety record. An integrated analysis by the manufacturer of data from 20,000 vaccinees in the safety database obtained in the strict monitoring conditions of clinical trials of the vaccine revealed a higher risk of solicited local or systemic reactions, but no increase in severe adverse effects or longer-term consequences.23
Similarly, safety studies with high-dose trivalent influenza vaccine showed a small increase in local injection site reactions, most commonly pain at the site, and some increase in systemic adverse event rates. These reactions were largely mild and self-limiting. Again, no increase in the rate of serious adverse events was seen.24
Timing of influenza vaccination in older people
Recent data on influenza vaccine effectiveness over the course of the influenza season suggest that in a predominant H3N2 season, vaccine effectiveness falls about 8% per month; vaccine may no longer be effective four months after administration. This has led to debate about delaying vaccination until around May in older people in Australia to ensure they remain protected later in the influenza season.
Data show continued immunological markers for more than six months after administration of adjuvanted trivalent influenza vaccine, so timing may be less crucial with this vaccine. Nevertheless, substantial influenza activity before June is uncommon, and delaying vaccine until May appears reasonable.
Role of general practice
Vaccination is an important component of promoting healthy ageing. Current coverage rates with influenza vaccine in older people are too low, at about 75%.25 This coverage level would not be accepted in children, and in view of the clear benefit of vaccination and the amount of influenza- associated disease in older people, 75% coverage should not be accepted in this age group either. GPs are key to improving vaccination rates.26 Having a clear rationale about the high risk of influenza in older people and the benefit of vaccination with a new safe enhanced vaccine, and sharing this with all patients in target groups is important. This is particularly the case for those with chronic disease. Two case studies on influenza vaccination that illustrate this approach are shown in Box 2.
Influenza remains a major public health problem in Australia that causes significant severe disease, long-term disability and mortality in older people. The theoretical advantages of increasing the antigen content (high-dose trivalent influenza vaccine) or adding an adjuvant (adjuvanted trivalent influenza vaccine) has translated in real-world studies to improved protection for older people.
For this reason, the Australian Government Department of Health has made available and recommended the use of high-dose trivalent influenza vaccine or adjuvanted trivalent influenza vaccine in people aged 65 years and over. Adjuvanted trivalent influenza vaccine is also currently funded under the NIP for this age group. Healthcare practitioners should note recent recommendations and ensure that their older patients are offered seasonal vaccine designed specifically to protect older people. MT