Emulation of the target trial
We divided the baseline study period into weekly time blocks. Eligible individuals were allocated into these blocks according to their index dates. In each weekly time block we calculated the propensity score (PS) and adopted an overlap weighting approach to balance baseline characteristics (Fig. Selection process of participants for the emulation of a target trial evaluating the comparative effectiveness of the BNT162b2 and ChAdOx1 nCoV-19 vaccines