SARS-CoV-2(21) Patient(19) antibody(15) COVID-19(15) vaccination(14) Infection(14) Vaccine(13) T cell(13) significantly lower(11) convalescent(10) AZD1222(10) proportion(10) individual(10) vaccinees(10) less(10) severity(9) virus(9) dose(9) Blood(9) immune response(9) investigated(8) reported(8) marker(8) required(8) SARS‐CoV‐2(8) Critical(8) COVID‐19(8) Frequency(7) serum(7) tested(7)