On May 13, 2021, University of Oxford researchers reported that Com-COV study data comparing mixed dosing schedules of Pfizer / Oxford-AstraZeneca vaccines, showed increase in the frequency of mild-moderate symptoms in those receiving either mixed dosing schedule. Writing in a peer-reviewed Research Letter published in the Lancet, they reported that, when given at a four-week interval, both of the ‘mixed’ schedules (Pfizer-BioNTech followed by Oxford-AstraZeneca, and Oxford-AstraZeneca followed by Pfizer-BioNTech) induced more frequent reactions following the second ﾑboostﾒ dose than the standard, ‘non-mixed’ schedules.

‘Importantly, there are no safety concerns or signals, and this does not tell us if the immune response will be affected. We hope to report these data in the coming months. In the meantime, we have adapted the ongoing study to assess whether early and regular use of paracetamol reduces the frequency of these reactions.’

They also noted that as the study data was recorded in participants aged 50 and above, there is a possibility such reactions may be more prevalent in younger age groups.