Safety, immunogenicity, and reactogenicity of BNT162b2 and mRNA-1273 COVID-19 vaccines given as fourth-dose boosters following two doses of ChAdOx1 nCoV-19 or BNT162b2 and a third dose of BNT162b2 (COV-BOOST): a multicentre, blinded, phase 2, randomized trial

SARS-CoV-2 anti-spike protein IgG concentration, ELU/mL Day 28 after the third dose 23 325 (20 030–27 162); 66 25 317 (20 996–30 528); 66 20 502 (16 473–25 517); 35 21 980 (16 476–29 324); 33 26 982 (22 056–33 008); 31 29 161 (23 093–36 823); 33 Day 0 or fourth dose 3049 (2550–3646); 66 3469 (2730–4407); 66 2532 (1974–3247); 35 2571 (1874–3527); 34 3761 (2959–4780); 31 4769 (3421–6648); 32 Day 14 after the fourth dose 37 460 (31 996–43 857); 65 54 936 (46 826–64 452); 67 33 316 (26 942–41 198); 35 52 080 (41 163–65 894); 34 42 949 (34 148–54 019); 30 58 043 (46 693–72 150); 33 Fold change (day 14 after fourth dose vs day 28 after third dose) 1 59 (1 41–1 78); 65 2 19 (1 90–2 52); 66 1 62 (1 35–1 95); 35 2 41 (1 90–3 05); 33 1 54 (1 35–1 76); 30 1 99 (1 71–2 31); 33 Fold change (day 14 after fourth dose vs day 0 or fourth dose) 12 19 (10 37–14 32); 65 15 90 (12 92–19 58); 66 13 16 (10 24–16 91); 35 20·26 (15·09–27·21); 34 11 14 (9 21–13 47); 30 12 30 (9 39–16 11); 32 Cellular response (wild-type), spot forming cells per 106 PBMCs

Due to logistic reasons, only 50% of study sites collected cellular immunology samples (proximity to external laboratory) in the main COV-BOOST study; the cellular immunology samples after the fourth dose were collected in the immunology cohort.