NHS Evidence Health Information Resources formerly National Library for Health

The flu vaccination does not reduce hospital admissions among the elderly, reported four newspapers (24 October 2007). Some newspaper headlines overstate the results of a reliable study which found flu vaccination had no effect on whether over-65s with respiratory illness needed to be hospitalised.

Four newspapers (1-4) reported a failure of the flu vaccination to reduce hospital admissions among the elderly. One newspaper (1) stated that the flu vaccination is failing to save the lives of older people.
The reports were based on a study (5) which looked at whether elderly people with acute respiratory illness were admitted to hospital or successfully treated in the community, and compared the proportion of people in each group that had been given the flu vaccine before they became ill. The authors of the study reported that there was no significant difference between these two proportions. The study did not include those vaccinated elderly people who remained well or look at the effectiveness of the flu vaccine in preventing infection or death from flu.
Although all newspapers reported details of the study fairly accurately, in some cases the headlines (4) and leading paragraphs (1) suggesting that the annual flu vaccination for the elderly is ineffective are not based on the results or conclusions of this study. The study authors themselves caution against interpreting their results to mean that the influenza vaccine is not beneficial, only that it should not be relied upon to relieve the pressure for hospital beds in winter.

Evaluation of the evidence base for the effect of the flu vaccine on hospital admission for acute respiratory illness

Where does the evidence come from?

The evidence is from a study conducted by researchers from the Health Protection Agency and several British hospitals and universities as part of a wider investigation of the risk factors for winter respiratory hospital admissions. The main source of funding was a grant from the British Lung Foundation.

What were the authors' objectives?

The aim of the study was to examine the effect of routine influenza vaccine on acute respiratory hospitalisations of elderly patients with acute respiratory illness in the winter.

What was the nature of the evidence?

This was a case-control study taking participants from a cohort of older people registered with 79 general practices in central England. A total of 3970 people aged 65-89 years who had consulted their GP or other emergency medical service for an acute episode of respiratory infection or exacerbation of existing disease between October 2003 and March 2004 were identified for the study. Cases were defined as patients admitted to hospital with acute respiratory disease. Among the cohort there were 500 cases however sufficient information for full analysis were only obtained from 157 of these. Controls were defined as patients presenting with acute respiratory disease who were managed in the community. Controls were matched to cases for age, sex and consultation date, and of the 3470 identified, 639 were included in the full analysis.

How did participants differ on their levels of exposure to the factor of interest?

The researchers were interested in whether participants had received the recommended influenza vaccine for 2003-2004 at least 3 weeks prior to their entry to the study. Among the 500 cases, 61.8% had received the vaccine, compared with 66.5% of the 3470 controls (values for the cases and controls included in the full analysis were 74.5% and 74.2%, respectively).

What were the findings?

There was no significant effect of influenza vaccine on hospital admission among patients presenting with respiratory illness. This held true when age, sex, chronic obstructive pulmonary disease and other chronic medical conditions, previous hospital admissions, smoking status, functional score, ethnicity and rurality of patients were taken into account in the analysis.

What were the authors' conclusions?

The authors concluded that the flu vaccination did not prevent hospitalisation among elderly patients with acute respiratory disease.

How reliable are the conclusions?

This appears to be a well-conducted study with a reliable conclusion. The study participants were drawn from a representative UK population and cases and controls were matched appropriately. Although only 20% of eligible participants were included in the full analysis, some results from the full cohort were presented, and the potential effects of this shortfall were investigated. Differences between participants in factors such as age, gender, underlying medical conditions, smoking status, and ethnicity were accounted for in the analysis, and conclusions were drawn only from analyses with adequate statistical power. The implications of the study were discussed. In particular the authors cautioned against interpreting their results to mean that the influenza vaccine is not beneficial, only that it should not be relied upon to relieve the pressure for hospital beds in winter.

Systematic reviews

Information staff at CRD searched for systematic reviews relevant to this topic. Systematic reviews are valuable sources of evidence as they locate, appraise and synthesize all available evidence on a particular topic.

There was one related systematic review identified on the Cochrane Database of Systematic Reviews (CDSR) (6) and three on the Database of Abstracts of Reviews of Effects (DARE) (7-9).

References and resources

1. Flu jab 'failing to save the elderly'. The Times, 24 October 2007, p29.

2. Question mark over flu jabs. Daily Mail, 24 October 2007, p1,4.

3. Flu jabs 'fail to cut illnesses'. Daily Telegraph, 24 October 2007, p1.

4. No point giving flu jabs to over-65s, say doctors. Daily Express, 24 October 2007, p32.

5. Jordan RE, Hawker JI, Ayres JG, Tunnicliffe W, Adab P, Olowokure B, et al. A case-control study of elderly patients with acute respiratory illness: effect of influenza vaccination on admission to hospital in winter 2003-2004. Vaccine 2007;doi:10.1016/j.vaccine.2007.09.005.

6. Rivetti D, Jefferson T, Thomas R, Rudin M, Rivetti A, Di Pietrantonj C, Demicheli V. Vaccines for preventing influenza in the elderly. Cochrane Database of Systematic Reviews 2006, Issue 3. Art. No.: CD004876. DOI: 10.1002/14651858.CD004876.pub2.

7.Gross PA, Hermogenes AW, Sacks HS, Lau J, Levandowski RA. The efficacy of influenza vaccine in elderly persons: a meta-analysis and review of the literature. Annals of Internal Medicine 1995;123(7):518-27. [DARE Abstract]

8. Puig-Barbera J, Marquez-Calderon S. Efectividad de la vacunacion antigripal en los ancianos: una revision critica de la bibliografia [Influenza vaccine effectiveness in the elderly: a critical literature review]. Medicina Clinica 1995;105(17):645-8. [DARE Abstract]

9. Villari P, Manzoli L, Boccia A. Methodological quality of studies and patient age as major sources of variation in efficacy estimates of influenza vaccination in healthy adults: a meta-analysis. Vaccine 2004;22(25-26):3475-86. [DARE Abstract]