Table 3.

Estimation of VE_a Over Successive Time Periods Based on Antibody Tests Under No Crossover (A), Blinded Priority-Dependent (B) and Priority-Independent (C) Crossover, and Unblinded Priority-Dependent (B’) and Priority-Independent (C’) Crossover When Vaccine Efficacy Wanes Over Time

Design	Weeks	True VEa (%)	Proposed Method				Naive Method
			Mean (%)	SE (%)	SEE (%)	CP (%)	Mean (%)	SE (%)	SEE (%)	CP (%)
A	0–4	50.3	50.3	3.1	2.7	91	58.3	3.6	3.5	42
	4–16	75.3	75.3	2.6	2.3	92	82.9	3.0	2.9	39
	16–28	62.9	62.9	2.7	2.9	96	68.0	1.9	1.9	26
	28–40	44.3	43.2	10.8	10.3	93	38.7	8.4	8.2	91
B	0–4	50.3	50.1	2.1	2.0	95	61.5	1.6	1.5	0
	4–16	75.3	75.2	1.9	1.9	94	87.6	1.2	1.2	0
	16–28	62.9	63.1	2.3	2.3	96	79.8	1.3	1.3	0
	28–40	44.3	44.7	6.6	6.5	94	66.8	2.8	2.8	0
C	0–4	50.3	50.2	1.9	1.9	94	62.5	1.6	1.6	0
	4–16	75.3	75.3	1.9	1.9	95	88.8	1.2	1.3	0
	16–28	62.9	63.0	3.1	3.0	95	82.2	1.7	1.7	0
	28–40	44.3	44.1	8.0	7.9	95	71.5	3.6	3.6	0
B’	0–4	50.3	49.9	2.3	2.3	95	43.5	2.7	2.9	28
	4–16	75.3	75.0	2.0	2.0	96	70.2	2.7	2.8	50
	16–28	62.9	62.9	2.6	2.5	95	66.4	1.8	1.9	56
	28–40	44.3	44.5	8.1	7.9	95	61.8	3.5	3.5	1
C’	0–4	50.3	49.7	2.6	2.6	95	41.7	3.4	3.4	23
	4–16	75.3	74.9	2.0	2.1	95	69.3	2.9	2.9	38
	16–28	62.9	63.1	4.8	4.8	94	68.5	2.7	2.8	56
	28–40	44.3	44.5	15.1	14.8	94	67.0	6.4	6.5	19

Mean and SE denote the mean and standard error of the vaccine efficacy estimator, SEE denotes the mean of the standard error estimator, and CP denotes the coverage probability of the 95% confidence interval.

Abbreviation: VE_a, vaccine efficacy on attack rate.