Vials of the AstraZeneca and Pfizer-BioNTech Comirnaty coronavirus disease (COVID-19) vaccines are pictured in a General practitioners practice in Berlin, Germany, April 10, 2021. [Photo/Agencies] Combining different jabs would allow inoculation campaigns more flexibility Alternating doses of COVID-19 vaccines from Pfizer and AstraZeneca provides a robust immune response against the novel coronavirus, according to a United Kingdom study which could have significant implications for global vaccine rollout. An Oxford University-led trial of 830 volunteers showed that a mixed schedule of the vaccines induced high concentrations of antibodies against the COVID-19 spike protein when doses were administered four weeks apart, researchers said in a study published on The Lancet's preprint server.