Amid the global shortage of the COVID-19 vaccines, a study conducted by Oxford University has found out that alternating doses of the AstraZeneca and Pfizer-BioNTech vaccines generate robust immune responses against the coronavirus.

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According to the study, 'mixed' schedules of these vaccines induced high concentrations of antibodies against the SARS-CoV2 spike IgG protein when doses were administered four weeks apart. This study, published on The Lancet pre-print server, means all possible vaccination schedules involving the Oxford-AstraZeneca and Pfizer-BioNTech vaccines could potentially be used against COVID-19.

"The Com-COV study has evaluated 'mix and match' combinations of the Oxford and Pfizer vaccines to see to what extent these vaccines can be used interchangeably, potentially allowing flexibility in the UK and global vaccine roll-out", said Professor Matthew Snape, Associate Professor in Paediatrics and Vaccinology at the University of Oxford, and Chief Investigator on the trial.

"The results show that when given at a four-week interval both mixed schedules induce an immune response that is above the threshold set by the standard schedule of the Oxford/AstraZeneca vaccine". Professor Snape said these results are an invaluable guide to the use of mixed dose schedules, but the interval of four weeks studied here is shorter than the eight to 12-week schedule most commonly used for the Oxford-AstraZeneca vaccine. Meanwhile, UK Deputy Chief Medical Officer Professor Jonathan Van-Tam said: "Today's data is a vital step forward, showing a mixed schedule gives people protective immunity against COVID-19 after four weeks".

"Our non-mixed (homologous) vaccination programme has already saved tens of thousands of lives across the UK but we now know mixing doses could provide us with even greater flexibility for a booster programme, while also supporting countries which have further to go with their vaccine rollouts and who may be experiencing supply difficulties". The University of Oxford is leading the Com-COV study, run by the National Immunisation Schedule Evaluation Consortium (NISEC). This UK government funding study aims to evaluate the feasibility of using a different vaccine for the initial 'prime' vaccination to the follow-up 'booster' vaccination.