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Study design. (A) is the study flowchart. (B) shows the vaccination and survey timelines. ChAdOx1 #1, the first dose of ChAdOx1; BNT162b2 #1, the first dose of BNT162b2; BNT162b2 #2, the second dose of BNT162b2. * The schedule of the second dose of ChAdOx1 was not reached during the study period.
