Table 1.

Isotype analysis of anti-S antibodies

			103 Reciprocal end point titer*					IgG2a,c/IgG1 ratio
Strain	Vaccine	IgA	IgG1	IgG2a†	IgG2b	IgG2c‡	IgG3	IgG2a/IgG1	IgG2c/IgG1
BALB/c	2P × 2§	ND¶	102	1,005	26	—	4	9.85	—
	2P/RBD#	ND	102	1,600	64	—	6	15.69	—
	RBD/RBD‖	ND	102	16	2	—	0	0.16	—
C57BL/6	2P × 2§	ND	16	—	102	409	4	—	25.56
	2P/RBD#	ND	26	—	102	1,005	6	—	39.24
K18-hACE2	2P × 2§	ND	26	—	102	409	2	—	15.98
	2P/RBD#	ND	26	—	256	409	6	—	15.98

^*Mean of duplicates of pooled sera.

^†Gene not present in C57BL/6 and K18-hACE2 mice.

^‡Gene not present in BALB/c mice.

^§The 2P followed by 2P.

^¶ND, not detected.

^#The 2P followed by RBD protein.

^‖‖RBD protein followed by RBD protein.