Study	Intervention name	Estimate effect		Unit of analysis	Time point	Type of assay	Population
Ella 2021a	Intervention: BBV152	Median (IQR)	55N (22 to 173.80)	Number of  SFCs per million PBMCs	28‐D1	IFN‐γ ELISpot	18–55 years
	Control: placebo	Median (IQR)	3 (1 to 23)
Logunov 2021	Intervention: Gam‐COVID‐Vac	Median (IQR)	32.77 (13.94 to 50.76)	IFN‐γ concentration pg/mL	28‐D1	IFN‐γ measured by ELISA	≥ 18 years
	Control: placebo	Median (IQR)	0.41 (0.11 to 0.85)
Liu 2021	Intervention: ChAdOx1/ BNT162b2	Geometric mean ratio (95% CI)	3.90 (95% CI 2.90 to 5.30)	Number of spot‐forming cells (SFCs) per million PBMCs	28‐D2	IFN‐γ ELISpot	≥ 50 years
	Control: ChAdOx1/ChAdOx1
	Intervention: BNT162b2/ChAdOx1		1.20 (95% CI 0.87 to 1.70)
	Control: BNT162b2/ BNT162b2
Hall 2021	Intervention: mRNA‐1273/mRNA‐1273 boost	Median	432 versus 67; 95% CI for the between‐group difference, 46 to 986	T‐cell counts – cells per million CD4+ T cells	28‐D3	Intracellular cytokine staining	Transplant recipients only
	Control: mRNA‐1273/placebo boost	Median
Bonelli 2021	Intervention: BNT162b2 or mRNA‐1273/ChAdOx1 boost	Median (IQR)	459 (133 to 722)	Number of SFCs per million PBMCs	7‐D3	IFN‐γ ELISpot	People currently receiving rituximab
	Control: BNT162b2 or mRNA‐1273/BNT162b2 or mRNA‐1273 boost	Median (IQR)	305 (171 to 416)
Zhang 2021	Intervention: CoronaVac	Median (Min, Max)	5.50 (0 to 35.70)	Number of SFCs per million PBMCs	14‐D2	IFN‐γ ELISpot	18–59 years
	Control: placebo	Median (Min, Max)	0 (0 to 11.70)
Sablerolles 2021	Intervention: Ad26.COV2.S/mRNA‐1273 boost	Percentage of responders	44/48 (91.66%) versus 32/44 (72.72%) (RR 0.79, 95% CI 0.64 to 0.96, P = 0.01726)	Number of responders (responder cut‐off is 0.15 IU/mL)	28‐D2	IFN‐y release assay	18–65 years
	Control: Ad26.COV2.S/Ad26.COV2.S boost
	Intervention: Ad26.COV2.S/BNT162b2 boost	Percentage of responders	43/47 (91.48%) versus 32/44 (72.72%) (RR 0.79, 95% CI 0.65 to 0.97, P = 0.01946)
	Control: Ad26.COV2.S/Ad26.COV2.S boost
	Intervention: Ad26.COV2.S/BNT162b2 boost	Percentage of responders	43/47 (91.48%) versus 44/48 (91.66%) (RR 1.00, 95% CI 0.88 to 1.13, P = 0.9753)
	Control: Ad26.COV2.S/mRNA‐1273 boost