Learning to Trust Flu Shots: Quasi‐Experimental Evidence from the 2009 Swine Flu Pandemic
利用2009年猪流感大流行期间不同疫苗推荐的自然实验，发现过去季节性流感疫苗接种经历对后续大流行疫苗接种有显著因果影响，表明学习机制在疫苗接种决策中起重要作用。
This paper studies consumer learning in influenza vaccination decisions. We examine consumer learning in influenza vaccine demand within a reduced form instrumental variable framework that exploits differences in risk characteristics of different influenza viruses as a natural experiment to distinguish the effects of learning based on previous influenza vaccination experiences from unobserved heterogeneity. The emergence of a new virus strain (influenza A H1N1/09) during the 2009 'Swine flu' pandemic resulted in two different vaccines being recommended for distinct population subgroups with some people, who were not usually targeted by seasonal vaccination programs, being specifically recommended for the new Swine flu vaccine. We use these differences in vaccination targeting to construct instrumental variables for estimating the effect of past influenza vaccination experiences on the demand for pandemic vaccine. We find large causal effects of previous seasonal vaccination on pandemic vaccination. Causal effects of past influenza vaccination experiences on perceived vaccination safety are likely to be an important pathway linking past vaccination experiences with future vaccine uptake. Our results suggest a significant role of learning in vaccination decisions. Current efforts to expand seasonal vaccination may thus have potentially important long-term effects on future influenza vaccination levels and pandemic preparedness. Copyright © 2016 John Wiley & Sons, Ltd.