This is a herd immunity model that incorporates the effects of different cohorts in the population having different activity levels and social interaction levels between groups, reflecting age groups and high/low socializing population segments.
two main conclusions are that
-
Herd immunity is reached much sooner when these effects are included, with most of the effect coming from the variation in activity levels. For example, you could get a herd immunity at 43% instead of 60% for a virus with R0=2.5.
-
Social distancing type strategies can reduce the number of cases overall, but there is a level at which the harshest measures actually increase the number of cases when eventually relaxed, since they stamp out the virus before it reaches herd immunity and then there’s a second wave outbreak that overshoots and gets more people than were necessay than if your lockdown was just strict enough to get to herd immunity