Table 4.

Antibody Titer between the Vaccine and Placebo Groups.

Antibody Titer	Time Point	Parameter	Group		p-value
			Vaccine (N = 397)	Placebo (N = 133)
IgG (ELISA)	V1	Seropositive rate n(%) (95% CI)	44 (11.08) (8.36–14.55)	14 (10.53) (6.37–16.89)	0.859**)
		GMT*) (95% CI) Median	220.27 (212.87–227.93) 200.00	220.37 (206.45–235.24) 200.00	0.990***)
	V3	Seropositive rate n(%) (95 %CI) Seroconversion n(%) (95% CI) GMT*) (95% CI) Median	396 (99.74) (99.26–100) 387 (97.48) (95.43–98.63) 5181.19 (4746.13–5656.14) 5333.35	7 (5.29) (1.47–9.06) 1 (0.75) (0.13–4.14) 223.61 (209.08–239.47) 200.00	<0.001**)  < 0.001**)  < 0.001***)
Neutralization Antibody	V1	Seropositive rate n(%) (95% CI) GMT*) (95% CI) Median	0 (0–0.96) 2.00 (−) –	0 (0–2.81) 2.00 (−) –	– –
	V3	Seropositive rate n(%) (95% CI) Seroconversion n (%) (95% CI) GMT*) (95% CI) Median	380 (95.72) (93.25–97.31) 346 (87.15) (83.50–90.09) 15.76 (14.57–17.04) 16	1 (0.75) (0.13–4.14) 0 (0.00) (0–2.81) 2.02 (1.98–2.05) 2	<0.001**)  < 0.001**)  < 0.001***)

*) The comparison results after logarithmic transformation. **) Chi-square test; ***) t-test.

V1 = before injection;

V3 = 14 days after second injection;

IgG seropositive = titer > 200; seroconversion = four-fold increasing anti-RBD antibody IgG titer compare to baseline 14 days after the second dose.

Antibody neutralization seropositive = titer ≥ 1:4; seroconversion = a change from seronegative (titer < 1:8) to seropositive (titer ≥ 1:8); or a 4-fold increase from baseline titers if titer at baseline ≥ 1:8.