Immunogenicity, safety, and reactogenicity of heterologous COVID-19 primary vaccination incorporating mRNA, viral-vector, and protein-adjuvant vaccines in the UK (Com-COV2): a single-blind, randomised, phase 2, non-inferiority trial

Background:Given the importance of flexible use of different COVID-19 vaccines within the same schedule to facilitate rapid deployment,we studied mixed priming schedules incorporating an adenoviral-vectored vaccine(ChAdOx1 nCoV-19[ChAd],AstraZeneca),two mRNA vaccines(BNT162b2[BNT],Pfizer-BioNTech,and mRNA-1273[m1273],Moderna)and a nanoparticle vaccine containing SARS-CoV-2 spike glycoprotein and Matrix-M adjuvant(NVX-CoV2373[NVX],Novavax).