Why COVID projections have become harder During the early days of the pandemic, simple models could be used to project the number of COVID cases and the likely effect on the population, including demands for health care.
Relatively few variables were needed to produce the first projections. That was because there was one main variant of COVID, the original strain, to which everyone in the world was susceptible.
But now, those simple assumptions no longer hold. Much of the world’s population is estimated to have had COVID and there are significant differences between individual levels of protection in terms of which vaccines, and how many doses, people have received around the world.
In total, 13 billion vaccine doses have been administered – but not equitably. Modelling also works well when people act in ways that are predictable, whether this is normal, pre-pandemic behaviour, or at times of severe social restrictions.