Speaker
Description
Novel variant emergence during viral outbreaks, as in the COVID-19 pandemic, undermines vaccine effectiveness. When a variant emerges, policy advisors must decide whether to recommend continuing booster vaccination with the existing vaccine or delaying until a variant-adapted vaccine is available. We present a mathematical model for evaluating these strategies by quantifying severe outcomes (deaths or Years of Life Lost; YLL), accounting for time-varying immunity. We compare two primary strategies: (1) boosting with the existing vaccine and (2) delayed boosting with a variant-adapted vaccine (after a development lag). If the updated vaccine is available within a threshold time, delaying vaccination leads to fewer deaths (or YLL). This threshold depends on characteristics including variant transmissibility, with more transmissible variants yielding shorter thresholds. We further explore mixed strategies involving vaccinating some individuals with the existing vaccine and others with the variant-adapted vaccine (when available). In a scenario motivated by the emergence of the SARS-CoV-2 Omicron variant, delaying all booster vaccination is optimal for short development times, whereas for longer development times vaccinating older individuals with the existing vaccine and younger individuals with the variant-adapted vaccine is preferable. Our modelling framework facilitates evidence-based decisions on vaccine updating and deployment during variant-driven outbreaks.
