Quantifying the impact of a broadly protective sarbecovirus vaccine in a future SARS-X pandemic

COVID-19 has underscored the need for more timely access to vaccines during future pandemics. This has motivated development of broad-spectrum vaccines providing protection against viral families, which could be stockpiled ahead of an outbreak and deployed rapidly following detection. We use mathematical modelling to evaluate the utility of a broadly protective sarbecovirus vaccine (BPSV) during a hypothetical SARS-X outbreak, including ring-vaccination, spatial targeting and mass vaccination of high-risk populations. Our results show BPSV ring- or spatially-targeted vaccination strategies are unlikely to contain a SARS-CoV-2-like virus but could contain or slow the spread of a SARS-CoV-1-like virus. Vaccination of high-risk populations with the BPSV ahead of a virus-specific vaccine (VSV) becoming available could substantially reduce mortality. For a 250-day VSV development timeline, BPSV availability reduced infection-related deaths in our model by 54% on average, though exact impact depended on the non-pharmaceutical intervention (NPI) scenario considered. We further show that BPSV availability enables shorter and less stringent NPIs to be imposed whilst limiting disease burden to that observed in the VSV-only scenario, though results are sensitive to vaccine properties (e.g. efficacy), health system capabilities (e.g. vaccination rollout speed) and the assumed timeline to VSV availability. Our modelling suggests that availability of a BPSV for those aged 60+ years could have averted 40-65% of COVID-19 deaths during the pandemics first year, with exact impact depending on the size of the maintained stockpile. Our work highlights significant potential impact of a BPSV, but that achieving this depends on investment into health systems enabling rapid and equitable access during future SARS-X pandemics.