Background
Covid-19 vaccination is critical for controlling the COVID-19 pandemic. The United Kingdom (UK) implemented a COVID-19 vaccination program after the emergency use approval of the Pfizer-BioNTech messenger RNA (mRNA) vaccine, BNT162b2, in December 2020 [Previous studies reported that the AdV vector vaccine might induce higher levels of specific T cells, whereas the mRNA vaccine might induce higher antibody titers [Therefore, we emulated a target trial to evaluate the comparative effectiveness of the BNT162b2 vaccine vs. the ChAdOx1 vaccine against COVID-19 using data from a UK primary care database.