The model uses scenarios to explore the potential paths the pandemic may take under future conditions. Model projections take a variety of factors into account, including current variants, vaccine uptake, vaccination/boosting rates, previous infection, waning immunity, weather, and behavioral responses. Unless a different variant is specified, models are based on the transmission dynamics of the BA.5 subvariant. All models now account for bivalent boosters. Unless otherwise specified, they assume that booster administrations will continue at the current pace matching the 3rd dose rollout.
The Adaptive scenario represents the current course of the pandemic, projecting it forward with no major changes.
The VariantX modifier explores the potential impact of a new variant emerging in the next few months. This hypothetical variant is imagined as having the same immune escape and transmissibility advantages over BA.4/5 that BA.4/5 did over the earlier BA.2. See page three of the July 15 report for details.
The FallWinter modifier layers seasonal increases associated with colder weather, holiday gatherings, and travel, on top of the base scenarios. It does this by artificially adjusting transmissibility between September and January to match transmissibility from the same time last year.
The new "OptBooster" (optimistic) modifier assumes that bivalent booster coverage will increase beyond the current pace and be 25% higher than 3rd dose boosters from Fall of 2021. The new "NoMoreBooster" (pessimistic) modifier assumes administrations will slow down and stop at current levels.