Modelling the impact of Omicron and emerging variants on SARS-CoV-2 transmission and public health burden

Plain Language SummarySARS-CoV-2 has mutated over time, resulting in new variants of the virus becoming the most common variant present in a population. The mutations that might alter characteristics of the virus, such as increasing the ability to infect people (infectivity), produce more severe illness (severity), or reduce the response of the immune system, are described as variants of concern (VOCs). We used a mathematical model of SARS-CoV-2 transmission to show that the infectivity of a future variant is the primary determinant of whether it will become most common, but that this increased ability to infect people does not always lead to an increased public health burden. Increasing vaccination is projected to have the biggest public health benefit for highly infective, severe variants that the immune system responds to. However, variants that do not respond to any previously gained immunity, even if less severe, would require alternative measures for control. These findings provide quantitative guidance when preparing for emerging VOCs. BackgroundSARS-CoV-2 variants of concern, such as Omicron (B.1.1.529), continue to emerge. Assessing the impact of their potential viral properties on the probability of future transmission dominance and public health burden is fundamental in guiding ongoing COVID-19 control strategies.MethodsWith an individual-based transmission model, OpenCOVID, we simulated three viral properties; infectivity, severity, and immune-evading ability, all relative to the Delta variant, to identify thresholds for Omicron's or any emerging VOC's potential future dominance, impact on public health, and risk to health systems. We further identify for which combinations of viral properties current interventions would be sufficient to control transmission.ResultsWe show that, with first-generation SARS-CoV-2 vaccines and limited physical distancing in place, a VOC's potential future dominance is primarily driven by its infectivity, which does not always lead to an increased public health burden. However, we also show that highly immune-evading variants that become dominant, even in the case of reduced variant severity, would likely require alternative measures to avoid strain on health systems, such as strengthened physical distancing measures, novel treatments, and second-generation vaccines. Expanded vaccination, that includes a booster dose for adults and child vaccination strategies, is projected to have the biggest public health benefit for a highly infective, highly severe VOC with low immune-evading capacity.ConclusionsThese findings provide quantitative guidance to decision-makers at a critical time while Omicron's properties are being assessed and preparedness for emerging VOCs is eminent. We emphasise the importance of both genomic and population epidemiological surveillance. Le Rutte, Shattock et al. develop an individual-based SARS-CoV-2 transmission model to identify thresholds for dominance, health impact, risk to health systems, and required interventions for emerging variants of concern. This model shows that even if an emerging variant is less severe, first generation vaccines might not be sufficient to avoid overloaded health care systems.

Automated summary

This study shows that the infectivity of future variants is the primary determinant of whether it will become most common, but this increased infectivity does not always lead to an increased public health burden. Increasing vaccination, especially for highly infectious and severe variants that the immune system responds to, is projected to have the biggest public health benefit.