Necessary conditions for the future consideration of vaccine certificates.

Vaccine certificates were deployed during the COVID-19 pandemic to enable the partial restoration of social and economic activities whilst protecting the public's health. Despite widespread adoption, their use was (and remains) controversial, especially because of concerns regarding their impact on liberty. Getting clarity on the conditions under which vaccine certificates should and should not be considered is critical as the world prepares for future infectious disease threats, including those that may differ substantially from the COVID-19 pandemic. To this end, we offer a framework which argues that as three key factors increase - the pathogenicity of the infectious disease, the prevalence of the infectious disease, and the protective effects of its associated vaccine - so, too, does the pro tanto justification for considering the use of vaccine certificates, while lower levels diminish the justification. This is because higher 'scores' for each of these dimensions will provide stronger justification for trade-offs with liberty that are likely to occur as a result of vaccine certificate use. While not a comprehensive framework for evaluating the use of vaccine certificates, these three conditions comprise a framework that can aid decision-makers in determining whether vaccine certificates are worthy of further consideration in the face of a future threat.