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With concern surrounding uptake of vaccine in at-risk under-65s,

Dr Douglas Fleming looks at the arguments for extending the programme

Influenza vaccination policy is based on targeting groups at increased risk. We vaccinate about 70 per cent of the elderly and 18 per cent of the total population.

But risk is a relative concept and depends where the line is drawn. In the US people aged over 50 are now included in the target group because there is evidence that hospital admissions with respiratory illnesses during flu epidemics rise appreciably beyond this age, partly because of increased co-morbidity. Increased admissions beyond age 50 have also been reported in England1.

In some countries children have been routinely vaccinated against influenza each year partly for their own protection but partly also to limit the spread of the disease. After this practice was abandoned in Japan, death rates in older people during influenza epidemics started to rise.

In the US, vaccination is recommended for women in the second and third trimesters of pregnancy because of increased risk to the mother and adverse outcome.

Should we be vaccinating more people?

If vaccination were effective for five to 10 years there would be a strong case for universal vaccination, but influenza viruses are constantly mutating, necessitating annual vaccination.

The vaccine, item-of-service fee and publicity campaign cost around 100 million per year for current policy. This has been shown to be cost-effective by limiting hospital admissions and reducing deaths; it compares favourably with other preventive health care interventions. Improving uptake in younger people with co-morbidity needs to be our first priority.

Expansion of the vaccination target groups is kept under review by the influenza subgroup of the Joint Committee on Vaccination and Immunisation, which advises the Government on immunisation policy recommendations. Decisions are made taking into account:

- The clarity with which groups at increased risk can be defined

- The cost-effectiveness of intervention by vaccination

- The likely acceptance of vaccination in the community

G The feasibility of mass vaccination programmes.

Very high rates of vaccine uptake are needed if the community at large is to benefit from limiting transmission of the disease.

We also need to recognise the benefits of treatment (and sometimes prophylactic intervention) with neuraminidase inhibitor antivirals. But these are limited in less severe cases of influenza and lost if treatment is not started within two days of onset.

The need for early treatment is not unique to neuraminidase inhibitors: it has been shown previously for amantadine drugs used to treat influenza and for aciclovir used to treat varicella zoster infections.

There is also some evidence from clinical trials of neuraminidase inhibitor antivirals that influenza has a greater impact on people aged over 50.

New vaccines

A vaccine to protect long-term against all strains of influenza, including new potentially pandemic strains, would be a major breakthrough. But no such vaccine is on the horizon.

Nevertheless, new vaccines are continuously introduced to provide higher levels of immunity. There is a particular need to achieve this in the oldest age group since the immune response mechanism deteriorates with age.

Two particular approaches have been used. The first is to enhance existing vaccines by using vaccine adjuvants. These provoke improved response as measured by virus antibody titre levels.

The second is to use a modified live virus instead of inactivated, destroyed virus material. Theoretically, live virus might be expected to induce an appropriate local cellular response and greater immunity. Live viruses have been used intermittently over the last 50 years, but interest has been reawakened with results from clinical trials of a cold adapted live vaccine administered by inhalation through the nose2.

While many of these developments are encouraging, they inevitably come at a price.

All have to be evaluated in terms of the existing options for managing this commonly underestimated problem.

Further information

The recommendations of the Advisory Committee on Immunisation Practices in the USA: www.cdc.gov/mmwr/preview/mmwrhtml/rr5208a1.htm

References

1 Bridges C et al. Prevention and control of influenza. Recommendations of the Advisory Committee on Immunisation Practices (ACIP). MMWR Recommendations and Reports 2003;52(RR08):1-36

2 Belshe RB et al. The efficacy of live attenuated, cold-adapted, trivalent, intranasal influenza virus vaccine in children. N Engl J Med. 1998;338(20):1405-12

Douglas Fleming is director of the RCGP Birmingham research unit and a member of the Joint Committee on Vaccination and Immunisation

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