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.

This means all possible vaccination schedules involving the Oxford-AstraZeneca and Pfizer-BioNTech vaccines could potentially be used against COVID-19.

Of note is that the order of vaccines made a difference, with an Oxford-AstraZeneca/Pfizer-BioNTech schedule inducing higher antibodies and T-cell responses than Pfizer-BioNTech/Oxford-AstraZeneca, and both of these inducing higher antibodies than the licensed, and highly effective ‘standard’ two-dose Oxford-AstraZeneca schedule. The highest antibody response was seen after the two-dose Pfizer-BioNTech schedule, and the highest T cell response from Oxford-AstraZeneca followed by Pfizer-BioNTech.

The trial recruited 830 volunteers aged 50 and above from eight National Institute for Health Research (NIHR) supported sites in England to evaluate the four different combinations of prime and booster vaccination.