ESWI – Third European Influenza Conference Vilamoura, Portugal, 14-17 September 2009

Volume 27, Issue 45, Pages 6269-6392 (23 October 2009)

This issue covers presentations made at ESWI – Third European Influenza Conference
Vilamoura, Portugal, 14-17 September 2008.

Influenza vaccination and mortality benefits: New insights, new opportunities
Pages 6300-6304
Lone Simonsen, Cecile Viboud, Robert J. Taylor, Mark A. Miller, Lisa Jackson

Influenza vaccination control strategies in most countries rely on vaccination of seniors and other high risk groups. Although placebo-controlled randomized trials show influenza vaccine is effective in younger age groups, few seniors >70 years were studied even though they suffer >90% of influenza-related deaths. Excess mortality studies could not confirm a national decline in influenza-related mortality while vaccine coverage quadrupled. Cohort studies have consistently reported that vaccination reduces all-cause winter mortality by 50%, an astonishing claim given only 5% of all winter deaths are attributable to influenza. This VE overestimation has now been attributed to profound confounding frailty selection bias. A way forward includes a new generation of unbiased studies with laboratory endpoints, and requires an agreement that the evidence base was flawed. The latter may clear the way for more immunogenic vaccines for seniors and exploration of other influenza control strategies

Challenges in evaluating influenza vaccine effectiveness and the mortality benefits controversy
Pages 6305-6311
Kristin L. Nichol

Randomized, controlled trials are the gold standard study design. However, ethical constraints and practical considerations may necessitate other types of studies for evaluating influenza vaccine effectiveness in the elderly—a high priority group for annual vaccination in many countries. Observational studies therefore comprise the bulk of the vaccine effectiveness evidence in older persons, but these types of studies can be susceptible to selection bias and residual confounding. All observational studies should utilize strategies to minimize the impact of bias and confounding. Recent studies questioning the plausibility of reported mortality benefits among vaccinated elderly persons may themselves be based on assumptions that are susceptible to important limitations and multiple biases. Future studies that incorporate prospectively collected information on functional status, life expectancy, and other types of data may provide additional insights into these concerns. At present, even after taking into account the potential for residual bias and confounding, most studies confirm the benefits of vaccination among the elderly for reducing hospitalization and death.

Internet-based monitoring of influenza-like illness in the general population: Experience of five influenza seasons in the Netherlands
Pages 6353-6357
I.H.M. Friesema, C.E. Koppeschaar, G.A. Donker, F. Dijkstra, S.P. van Noort, R. Smallenburg, W. van der Hoek, M.A.B. van der Sande

Like in most other countries, influenza surveillance in The Netherlands is based upon influenza-like illness (ILI) consultations reported by sentinel general practitioners (GP). In addition, an internet-based monitoring of ILI in the general population started in 2003/2004 (Great Influenza Survey (GIS)). We compared GIS results over 5 influenza seasons with results from the GP system. Weekly ILI incidence from GIS correlated well with ILI incidence from the GP system the same week and even better 1 week later. This suggests that GIS is useful for early detection of trends in influenza activity. However, two important vulnerable groups, children and the elderly, are clearly underrepresented in the GIS. Furthermore, virological confirmation is lacking in the GIS. So, GIS can be a useful addition to the GP system, especially when representativeness can be improved and when participation remains at the current high level.

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