Risk-Driven Responses to COVID-19 Eliminate the Tradeoff between Lives and Livelihoods (preprint)

Summary Background Responses to COVID-19 pandemic are conditioned by a perceived tradeoff between saving lives and paying the economic costs of contact-reduction measures. We develop and test the hypothesis that when populations endogenously respond to risk this tradeoff disappears. Methods We develop a model of SARS-CoV-2 transmission where populations endogenously reduce contacts in response to risk of death. We estimate the model for 118 countries constituting 7.05 billion people and assess the existence of a tradeoff between saving lives and livelihoods. Results We show that with endogenous responses communities go through three phases – rapid early outbreaks, control through initial response, and a longer period of quasi-equilibrium endemic infection with effective reproduction number (Re) fluctuating around one. Analytical characterization of this phase shows little tradeoff between contact reduction levels (underpinning economic costs) and death rates. Empirically estimating the model, we find no positive correlation (r = -0.241, p = 0.009) between (log) death rates and (normalized) contact levels across nations. While contact reduction levels are broadly similar across countries (5-95 percentile: 0.521-0.867 of pre-pandemic contacts), expected death rates vary greatly, by over two orders of magnitude (5-95 percentile: 0.03-17 deaths per million per day). Interpretation Whether by choice or by the force of crippling death tolls, most societies will bring down interactions enough to contain SARS-CoV-2’s spread. What we control is the severity of death toll required to compel us to act: greater responsiveness to risk can bring down deaths with no excess economic costs. Research in Context Evidence before this study We study how endogenous changes in behaviors, in response to risk of death, moderate the tradeoff between deaths and interaction levels in communities exposed to COVID-19 pandemic. We searched for existing models of SARS-CoV-2 transmission and how they incorporate changes in policies and behaviours in response to changing risk levels. Most common are the use of time-based changes in basic reproduction number to capture those behavioural responses, or empirically specified policies that have been enacted in response to the epidemic. These methods, while effective for empirical estimation of historical trajectories, do not inform the tradeoff we are seeking to understand. A smaller subset of prior work does include endogenous responses to risk, mostly in the form of policy switches that activate when risk exceeds some threshold, with notable exceptions that include continuous responses potentially more suitable for the study at hand. To our knowledge these prior formalizations do not focus on teasing out the perceived tradeoff between interaction levels in a community and public health burden of the epidemic. Therefore, the powerful intuition that a strong tradeoff exists between saving lives and livelihoods remains unchallenged. Added value of this study By introducing an endogenous and continuous response function connecting perceived risk levels to contact levels, we examine the existence of a tradeoff between contact levels and death rates across communities. We find this extension leads to a long quasi-equilibrium phase during which effective reproduction number remains around 1. During this phase our model predicts little tradeoff between contact reductions (the driver of economic costs) and death rates. We find empirical support for this extension and its predictions using data from 118 countries constituting more than 7 billion people. While countries show limited variation in their estimated contact reduction levels, deaths vary by two orders of magnitude. Implications of all available evidence In a pandemic individuals and communities respond to risk, not only by following government mandates, but also through their personal choices protecting their own and others’ lives. Formalizing this observation into models of contagion largely eliminates the tradeoff between saving lives and livelihoods in responding to a pandemic. More responsive policies promise to save lives with no additional economic costs compared to weaker response functions.