Influenza immunisation: is it cost effective for the older patient?

Influenza is a highly contagious acute respiratory disease that typically presents with a sudden onset of fever accompanied by a headache, sore throat, malaise and dry cough. In young healthy adults, the illness is usually self-limiting with the fever lasting between one and five days¹. However, in older people and those with chronic disease, influenza can be a serious illness and the resulting morbidity and mortality is often underestimated.

For example, during the last influenza epidemic to affect England and Wales (1989-90), it was estimated that 24,877 excess deaths occurred; 82 per cent of these were in individuals aged 75 years or older while only three per cent were in people aged less than 65 years². Institutional care, chronic obstructive pulmonary disease, asthma and neurological disease were all identified as independent risk factors for certified influenza death during this period³.

Influenza immunisation, using inactivated trivalent preparations containing antigens from two influenza A strains and one B strain is the cornerstone of current influenza prevention policy. Some studies have shown that immunisation can reduce mortality from influenza and pneumonia in both institutionalised and non-institutionalised older people, and may halve the incidence of influenza infection^3-8. Because of ethical concerns about the use of a placebo in frail older people, many of these studies were non-randomised and likely to have been affected by selection bias.

Influenza vaccine and healthcare resources

The uptake of influenza vaccine is affected by many factors including age, gender, health and socio-economic status, concern about adverse effects and prior utilisation of healthcare resources. A recent systematic review concluded that vaccination was most effective in people aged 65 years or older living in long-term care facilities, but it had only a modest effect on those living in the community⁹.

A cost benefit analysis usually translates health gains into pure monetary terms. Costs are weighted against the benefits and the outcome may be expressed by the benefit-to-cost ratio, where a value of greater than one indicates net cost savings. When the ratio is less than one, further quantification of health gains are needed using either a cost effectiveness or cost utility analysis.

A cost effectiveness analysis expresses net costs (costs minus benefits) in terms of health gains such as the number of infections avoided. A cost utility analysis takes into consideration the patient’s quality of life as well as number of life years gained from the intervention, and the quality adjusted life year (QALY) is used as an outcome measure. However, the practical problems of to be either ineffective or capable of causing significant side effects. Consequently, vaccine uptake in older people was typically poor, although this is now changing.

Intense efforts by doctors and policy makers to raise the profile of influenza – and recent media reports about the threat of a future pandemic from avian (H5N1) influenza – will no doubt help to increase the annual uptake of influenza vaccine still further. It is likely that in the future, age recommendations for influenza vaccination will fall and different groups will be targeted (e.g., children and healthy working adults) as further pharmacoeconomic data becomes available.

Greater vaccine uptake will then help to ensure that increased capacity and large-scale production of vaccine is possible in a pandemic situation when demand will be high. Future work should focus on initiatives to improve vaccine uptake in healthcare workers, which has remained low in many countries¹⁸. Vaccinating healthcare workers can reduce staff sickness during times of ‘winter pressure’ as well as reduce the transmission of influenza to frail older patients, which may help to reduce mortality¹⁹.

Key points:

• Influenza vaccination is a highly cost effective strategy in helping to reduce the economic consequences of influenza-associated morbidity and mortality in people aged over 65 years.
• Vaccination is most cost effective and even cost saving in the highest risk groups.
• Increasing vaccine uptake in the targeted groups will help to prepare for the next influenza pandemic.
• To reduce transmission of influenza to frail older patients initiatives need to be in place to encourage vaccine uptake amongst healthcare workers.

Dr Steve Allsup, Consultant physician at St Helens and Knowsley NHS Trust

References

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