The interpretation of vaccine efficacy estimands is subtle, even in randomized trials designed to quantify immunological effects of vaccination. In this article, we introduce terminology to distinguish between different vaccine efficacy estimands and clarify their interpretations. This allows us to explicitly consider immunological and behavioural effects of vaccination, and establish that policy-relevant estimands can differ substantially from those commonly reported in vaccine trials. We further show that a conventional vaccine trial allows identification and estimation of different vaccine estimands under plausible conditions, if one additional post-treatment variable is measured. Specifically, we utilize a ``belief variable'' that indicates the treatment an individual believed they had received. The belief variable is similar to ``blinding assessment'' variables that are occasionally collected in placebo-controlled trials in other fields. We illustrate the relations between the different estimands, and their practical relevance, in numerical examples based on an influenza vaccine trial.

翻译：疫苗效力估计值的解释是微妙的，即使在旨在量化疫苗接种免疫效应的随机试验中也是如此。本文引入了区分不同疫苗效力估计值的术语，并阐明其解释。这使得我们能够明确考虑疫苗接种的免疫效应和行为效应，并确立具有政策相关性的估计值可能与疫苗试验中通常报告的估计值存在显著差异。我们进一步证明，在合理的条件下，如果测量一个额外的治疗后变量，传统的疫苗试验能够识别和估计不同的疫苗估计值。具体而言，我们利用一个“信念变量”，该变量指示个体认为自己接受了哪种治疗。这个信念变量类似于其他领域安慰剂对照试验中偶尔收集的“盲法评估”变量。我们基于一项流感疫苗试验的数值示例，展示了不同估计值之间的关系及其实际相关性。