Reports of trials not included in the analysis (5 studies)
Type of vaccine	Reference	Register	Phase	Vaccine	Comparator	Sample size	Population/centre/location
RNA‐based vaccine	Chu 2021	NCT04405076	2	mRNA‐1273 (50 μg; 100 μg)	Placebo	600	Healthy adults/8 centres/USA
Inactivated virus	Feng 2021	ChiCTR2100041705; ChiCTR2100041706	*	BBIBP‐CorV D0/14; D0/21	BBIBP‐CorV D0/28	809	Healthy adults /single centre/China
Protein subunit	Pérez‐Rodríguez 2021	RPCEC00000338‐En	1	FINLAY‐FR‐1A (25 μg; 50 μg)	FINLAY‐FR‐1	60	Healthy adults/single centre/Cuba
Heterologous scheme	Borobia 2021	NCT04860739; EudraCT2021‐001978	2	BNT162b2 after 1 dose ChAdOx1‐S – 1 IM dose 30 μg/0.3 mL BNT162b2 8‐12 weeks after 1 dose ChAdOx1‐S	No second vaccine dose	676	Adults/multicentre/Spain
Non‐replicating viral vector/inactivated virus	Angkasekwinai 2022	TCTR20210720002		CoronaVac 3 μg	ChAdOx1 (5 × 1010 vp)	360	Healthcare workers/single centre/Thailand
Reports of trials already included in the analysis (7 studies)
RNA‐based vaccine	Pajon 2021	NCT04470427	3	mRNA‐1273	Placebo	791	Healthy adults/99 centres/USA
Non‐replicating viral vector	Voysey 2021b	NCT04324606; ISRCTN89951424; NCT04400838; NCT04444674	1/2/3	ChAdOx1 (5 × 1010 vp or 2.2 × 1010 vp)	Placebo/MenACWY	17, 177	Adults/multicentre/Brazil, South Africa and UK
	Stephenson 2021	NCT04436276	1	Ad26.COV2.S	Placebo	10	Healthy adults/single centre/USA
Inactivated virus	Pan 2021b	NCT04352608	2	CoronaVac (3 doses, 4 different schedules, 3 μg and 6 μg)	Placebo	600	Healthy adults/single centre/China
	Ella 2021a	NCT04471519	2	6 μg BBV152 + Algel‐IMDG	3 μg BBV152 + Algel‐IMDG	380	Healthy adults/9 centres/India
	Li 2021c	NCT04383574	1/2	CoronaVac (3 doses)	Placebo	350	Healthy adults aged ≥ 60 years/single centre/China
	Ella 2020b	NCT04471519	2	6 μg BBV152 + Algel‐IMDG	3 μg BBV152 + Algel‐IMDG	380	Healthy adults/9 centres/India