Field Effectiveness of Pandemic and 2009-2010 Seasonal Vaccines against 2009-2010 A(H1N1) Influenza: Estimations from Surveillance Data in France

BACKGROUND: In this study, we assess how effective pandemic and trivalent 2009-2010 seasonal vaccines were in preventing influenza-like illness (ILI) during the 2009 A(H1N1) pandemic in France. We also compare vaccine effectiveness against ILI versus laboratory-confirmed pandemic A(H1N1) influenza, and assess the possible bias caused by using non-specific endpoints and observational data. METHODOLOGY AND PRINCIPAL FINDINGS: We estimated vaccine effectiveness by using the following formula: VE  =  (PPV-PCV)/(PPV(1-PCV)) × 100%, where PPV is the proportion vaccinated in the population and PCV the proportion of vaccinated influenza cases. People were considered vaccinated three weeks after receiving a dose of vaccine. ILI and pandemic A(H1N1) laboratory-confirmed cases were obtained from two surveillance networks of general practitioners. During the epidemic, 99.7% of influenza isolates were pandemic A(H1N1). Pandemic and seasonal vaccine uptakes in the population were obtained from the National Health Insurance database and by telephonic surveys, respectively. Effectiveness estimates were adjusted by age and week. The presence of residual biases was explored by calculating vaccine effectiveness after the influenza period. The effectiveness of pandemic vaccines in preventing ILI was 52% (95% confidence interval: 30-69) during the pandemic and 33% (4-55) after. It was 86% (56-98) against confirmed influenza. The effectiveness of seasonal vaccines against ILI was 61% (56-66) during the pandemic and 19% (-10-41) after. It was 60% (41-74) against confirmed influenza. CONCLUSIONS: The effectiveness of pandemic vaccines in preventing confirmed pandemic A(H1N1) influenza on the field was high, consistently with published findings. It was significantly lower against ILI. This is unsurprising since not all ILI cases are caused by influenza. Trivalent 2009-2010 seasonal vaccines had a statistically significant effectiveness in preventing ILI and confirmed pandemic influenza, but were not better in preventing confirmed pandemic influenza than in preventing ILI. This lack of difference might be indicative of selection bias

Herding behaviour in strategic asset allocations: new approaches on quantitative and intertemporal imitation

In this article, we contribute to financial literature on institutional herding behaviour, intertemporal imitation and informational cascades by analysing the changes in the strategic asset allocations of Spanish equity pension plans investing in Eurozone equities. This article is mainly focused on methodological improvements. Firstly, the study examines the herding phenomenon by using the traditional measure developed by Lakonishok, Shleifer and Vishny (LSV) (1992). Afterwards, some original analyses such as the consideration of a restricted definition of buying and selling and the amount of the variations in the strategic allocations are carried out to overcome certain shortcomings existing in this metric. Moreover, we analyse the intertemporal imitation and the informational cascades through time-series regressions. The results show that Spanish pension managers are involved in herd behaviour, a phenomenon that is reinforced when important movements of the strategic allocations are required. Intertemporal analyses confirm the convergent behaviour of a significant number of pension plans; while the study of informational cascades allows us to discriminate between those plans that present anticipatory abilities and those that follow the strategic movements of the rest of the managers.