On Jun. 28, 2021, researchers running the University of Oxford-led Com-COV study reported that alternating doses of the Oxford-AstraZeneca and Pfizer-BioNTech vaccines generate robust immune responses against COVID-19.

In a paper published on the Lancet pre-print server, they report that both ‘mixed’ schedules (Pfizer-BioNTech followed by Oxford-AstraZeneca, and Oxford-AstraZeneca followed by Pfizer-BioNTech) induced high concentrations of antibodies against the SARS-CoV2 spike IgG protein when doses were administered four weeks apart.