A comparison of the test-negative and the matched case-control study designs for estimation of EV71 vaccine immunological surrogate endpoints from a randomized controlled trial

Figures & data

Figure 1. Study plan.

^#There were 7140 subjects who seeked medical care for suspected EV71 infected diseases in per-protocol population. 111 subjects missed EV71 NTAb titers data at Day 56. 49 tested positive as cases and 6980 tested negative as controls.

*The results were calculated based on 305 participants, including 51 EV71 cases (In phase III trial, there were totally 52 cases. One case excluded for no serum sample on day 56 was available) and 254 event-free participants as controls (Totally matched 255 controls. One control excluded for no serum sample at day 56 was available).

Table 1. Characteristics of cases and controls in test-negative design and matched case-control design.

		Test-negative design			Matched case-control
	Positive cases (49)	Negative controls (6980)	P value	EV71 cases (51)	Matched controls (254)	P value
Age*	19.8(8.3)	18.4(8.0)	.2268	19.7(8.2)	19.1(8.3)	.6275
Height	83.2(9.0)	81.4(8.1)	.1311	83.0(8.9)	82.0(8.7)	.4622
Weight	13.0(2.7)	12.5(2.2)	.0775	12.9(2.7)	12.4(2.2)	.1309
GMT	5.5(6.7)	109.9(20.1)	<.0001	5.0(6.0)	134.3(20.1)	<.0001
Received Vaccine	8(16.3%)	3469(49.7%)	<.0001	8(15.7%)	135(53.2%)	<.0001
Male	29(59.2%)	3940(56.5%)	.7002	29(56.9%)	133(52.4%)	.5567

*Age, Height, Weight, GMT were described by mean±SD. GMT = Geometric Mean Titer of EV71 NAb. Received vaccine and Male were showed by counts and percent. ANOVA was used to compare means and Chi-square test was used to compare the ratio.

Figure 2. Reverse cumulative curves for enterovirus 71 (EV71) neutralizing antibody titers about TND and MCC.

*EV71 neutralizing antibody titers data had been standardized.

Table 2. Sensitivity and specificity of different cutoff neutralizing antibody titer against EV71­associated disease by test-negative design and matched case-control design.

		Test-negative design			Matched case-control
Neutralizing antibody titer	Sensitivity* % (95% CI)	Specificity^ % (95% CI)	Youden index (sensitivity+specificity-1)	Sensitivity* % (95% CI)	Specificity^ % (95% CI)	Youden index (sensitivity+specificity-1)
1:4	71.4(56.7–83.4)	70.3(69.2–71.3)	0.4170	1.9(0.0–10.3)	99.6 (97.8–100.0)	0.0153
1:8	73.5(58.9–85.0)	69.3(68.2–70.4)	0.4277	73.1 (59.0–84.4)	74.3 (68.5–79.6)	0.4739
1:16	85.7(72.8–94.0)	65.9(64.8–67.0)	0.5162	84.6 (71.9–93.1)	70.8 (64.7–76.3)	0.5537
1:32	87.8(75.2–95.4)	63.9(62.8–65.0)	0.5165	88.5 (76.6–95.6)	66.0 (59.8–71.8)	0.5447
1:64	87.8(75.2–95.4)	61.0(59.8–62.1)	0.4871	88.5 (76.6–95.6)	63.2 (57.0–69.2)	0.5170
1:128	87.8(75.2–95.4)	56.3(55.2–57.5)	0.4409	90.4 (79.0–96.8)	57.3 (51.0–63.5)	0.4770
1:256	87.8(75.2–95.4)	48.5(47.3–49.7)	0.3628	90.4 (79.0–96.8)	49.4 (43.1–55.7)	0.3979
1:512	95.1(86.0–99.5)	38.4(37.3–39.6)	0.3434	94.2 (84.1–98.8)	41.9 (35.7–48.2)	0.3613
1:1024	98.0(89.1–99.9)	26.3(25.2–27.3)	0.2422	100.0 (93.2–100.0)	31.2 (25.6–37.3)	0.3123

*Sensitivity was defined as the proportion of EV71 cases having a titer <the cutoff value at day 56 in total EV71 cases.

^Specificity was defined as the proportion of matched controls having a titer ≥the cutoff values at day 56 in total matched controls.

Figure 3. The comparison of sensitivity, specificity, and Youden index between the TND and MCC.