Fig. 3: Predicting the effects of distributing vaccine doses between risk groups.

A Schematic of the allocation scenario. We assume that a first dose of vaccine has been administered to a high-risk group, and at some later time more vaccine becomes available. These vaccines could either be allocated as second doses to the high-risk group, or administered as a first dose to a lower-risk group. B Depending on the ratio of risk in the high-risk and lower-risk groups (x-axis), then the predicted ratio of cases averted by the one-dose compared to the two-dose strategy (y-axis) will vary. This will also vary with the spacing between doses (colours), with longer delays since first dose in the high-risk group favouring the strategy of a second dose to the high-risk group. The horizontal dashed line shows a ratio of one (i.e. where we flip from favouring a one-dose approach to favouring a two-dose approach). Results are shown for prevention of mpox of any severity. C The risk threshold (y-axis) is the risk ratio at which the optimal strategy changes from favouring a one-dose to favouring a two-dose regimen. The risk threshold predicted from the vaccine effectiveness reported in clinical studies is on the left (black), and the threshold estimated from model-based meta-analysis (including vaccine waning for vaccine administered at 4, 26, or 52 weeks) is shown on the right. Analysis in (B) and (C) is based on a low and constant force of infection. Shaded regions and error bars indicate 95% credible intervals.