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 report edthat, when given at a four-week interval, both of the ﾑmixedﾒ 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, ﾑnon-mixedﾒ schedules. The add that any adverse reactions were short lived and there were no other safety concerns.