Intrinsic and realized generation intervals in infectious-disease transmission

The generation interval is the interval between the time that an individual is infected by an infector and the time this infector was infected. Its distribution underpins estimates of the reproductive number and hence informs public health strategies. Empirical generation-interval distributions are often derived from contact-tracing data. But linking observed generation intervals to the underlying generation interval required for modeling purposes is surprisingly not straightforward, and misspecifications can lead to incorrect estimates of the reproductive number, with the potential to misguide interventions to stop or slow an epidemic. Here, we clarify the theoretical framework for three conceptually different generation-interval distributions: the ``intrinsic'' one typically used in mathematical models and the ``forward'' and ``backward'' ones typically observed from contact tracing data, looking respectively forward or backward in time. We explain how the relationship between thes...世代间隔（generation interval）指个体被传染源感染的时刻，与该传染源被感染的时刻之间的时间跨度。其分布为再生数的估算提供核心支撑，进而为公共卫生防控策略的制定提供科学依据。经验性世代间隔分布通常源自接触追踪数据。然而，将观测得到的世代间隔与建模所需的理论世代间隔进行关联，实则远非直观简便；若模型设定存在偏差，可能导致再生数估算失准，进而误导旨在遏制或减缓疫情传播的干预举措。本文厘清了三类概念迥异的世代间隔分布的理论框架：数学模型中常用的‘内在’世代间隔，以及分别通过时间前瞻与回溯的接触追踪数据所观测得到的‘前向’与‘后向’世代间隔。本文还阐释了三者之间的关联……