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Australian Journal of Pharmacy : May 2008
educatIon CuRRENT DRug INfoRMATIoN aJPcPd Dr Jack Thomas, OAM, PhD, MSc, FRPharms, FPS, consultant editor, AJP debate over effectiveness of influenza vaccination in elderly I nfluenza vaccination policy in Australia attempts to reduce the mortality burden of influenza by targeting people aged at least 65 years for vaccination. However, the effectiveness of this strategy is under debate.1 Study one Placebo-controlled randomised trials show influenza vaccine is effective in younger adults. However, few trials have included elderly people, and especially those aged at least 70 years. However, in the US this is the age- group that accounts for three-quarters of all influenza-related deaths. Some studies have been reported that suggest vaccine effectiveness declines sharply after age 70 and that antibody responses to flu vaccine in elderly people are only about one- quarter to one-half as strong as those in younger adults. Recent excess mortality studies were unable to confirm a decline in influenza-related mortality since 1980, even though vaccination coverage has significantly increased. Paradoxically, whereas studies in the US attribute about 5% of all winter deaths to influenza, many cohort studies report a 50% reduction in the total risk of death in winter; a benefit ten times greater than the estimated influenza mortality burden. New studies, however, have shown substantial unadjusted selection bias in previous cohort studies. The authors propose revisiting randomised controlled trials in elderly populations. However, they add that, while awaiting improved evidence base, elderly people should still continue to be vaccinated. It concluded: ‘Influenza causes many deaths every year, and even a partly effective vaccine would be better than no vaccine at all’. The authors of an accompanying editorial2 said, in their opinion, randomised, placebo-controlled trials are the only ethical and scientific way to have a definitive answer to the question of whether current flu vaccines protect elderly people. However, trials need to be large enough to detect rare outcomes and long enough to cover more than one flu season, they said. addressing potential bias and residual confounding in the results’.3 Data was pooled from 18 cohorts of community-dwelling elderly members of one US health maintenance organisation for 10 years, and was analysed to estimate the effectiveness of the vaccine in the prevention of hospitalisation for pneumonia or influenza and death, after adjustment for important covariates. There were 713,872 person- seasons of observation. Vaccination was associated with a 27% reduction in the risk of hospitalisation for pneumonia or influenza; and a 48% reduction in the risk of death. The results were analysed to eliminate a confounder that would have caused over-estimation of vaccine effectiveness. It was found that trIalS need to be large enough to detect rare outcomeS and long enough to cover more than one flu SeaSon. Study two Background: Reliable estimates of the effectiveness of influenza vaccine among people older than 65 years are important for informed vaccination policies and programs. Short-term studies may provide misleading pictures of long-term benefits, and residual confounding may have biased past results. This study examined the effectiveness of influenza vaccine in seniors over the long term while vaccination was still associated with statistically significant—though lower reductions in the risks of both hospitalisation and death. It concluded: ‘During 10 seasons, influenza vaccination was associated with significant reductions in the risk of hospitalisation for pneumonia or influenza and in the risk of death among community-dwelling elderly persons. Vaccine delivery to this high- priority group should be improved’. CoNTINuINg PRofESSIoNAL DEVELoPMENT In an editorial4 discussing the study it stated: ‘Overall, this study provides additional support for the current strategy to vaccinate elderly adults. The methodologic issues are important to debate, and doubt about the precise magnitude of the benefit of vaccination in this age group remains. However, there is no doubt that influenza is harmful and that the vaccine is beneficial and should be used widely. At the same time, it is clear that inactivated influenza vaccine is not a perfect solution to the problem. ‘About half of the winter time hospitalisations and deaths observed in this study occurred in the vaccinated population. Some of these deaths were probably due to other viruses, such as respiratory syncytial virus, that can mimic influenza, but many probably represent vaccine failures. Influenza vaccine is less immunogenic, and probably less effective, in older persons than in young healthy adults, and the development of safe but more immunogenic and effective vaccines for the elderly is an important goal’. n 1. Simonsen L, Taylor RJ, Viboud C, Miller MA, Jackson LA. Mortality benefits of influenza vaccination in elderly people: an ongoing controversy. Lancet Infect Dis. 2007;7:658–66. 2. Jefferson T, Di Pietrantonj C. Inactivated influenza vaccines in the elderly—are you sure? The Lancet 2007; 370:1199–1200. 3. Nichol KL, Nordin JD, Nelson DB, Mullooly JP, Hak E. Effectiveness of ifluenza vaccine in thecommunity-dwelling elderly. N Engl J Med 2007;357:1373–81. 4. Treanor JD. Influenza—The goal of control. N Eng J Med 2007;357:1439–41. THE AuSTRALIAN JouRNAL of PHARMACy VoL.89 MAy 2008 89