Validation and evaluation of serological correlates of protection for inactivated enterovirus 71 vaccine in children aged 6-35 months

Figures & data

Table 1. NTAb titers at day 56 post-vaccination and the incidence of EV71-associated disease in the per-protocol population (n=9654).

	Vaccine group	Placebo group
N	4817	4837	P value
GMT (95% CI)	788.4 (749.9,828.8)	14.6 (13.5,15.8)	<0.0001
N (cases/1000)	8 (1.7)	41 (8.5)	<0.0001

EV71, enterovirus 71; NTAb, neutralizing antibody; GMT, geometric mean titers; CI, confidence interval; N, the number of EV71-associated disease

Table 2. Estimates of parameters of logistic regression models used to evaluate risk of EV71-associated disease.

Parameter	β	SE	Wald	P value	OR (95% CI)
Logistic regression 1
Intercept	−3.125	0.473	43.678	<0.0001
Vaccination status	−1.637	0.387	17.885	<0.0001	0.195(0.091,0.416)
Logistic regression 2
Intercept	−4.349	0.570	58.269	<0.0001
Vaccination status	0.328	0.577	0.323	0.5699	1.388(0.448,4.297)
Day 56 antibody titers	−0.546	0.107	18.178	<0.0001	0.633(0.513,0.781)

SE, standard error; OR, odd ratio; CI, confidence interval.

Figure 1. Estimated curve of protection against EV71-associated disease versus neutralizng antibody titers at day 56 post-vaccination, with the estimated curve (solid line) is charted with 95% confidence interval (dashed line) in per-protocal population.

Figure 2. Estimated curves of protection against EV71-associated disease vs. neutralizng antibody titers at day 56 post-vaccination in vaccine (solid line) and placebo group (dashed line) in per-protocal population.

Table 3. Estimates of parameters of the scaled logit model by using procedure NLMIXED in the per-protocol population.

Paramter	Estimate	Standard Error	DF	P value	Lower	Upper
λ	0.0158	0.00682	9654	0.0205	0.00244	0.0292
α	−1.835	1.944	9654	0.345	−5.645	1.976
β	0.692	0.266	9654	0.0092	0.171	1.212

Table 4. Estimated day 56 antibody titers needed to provide various levels of protection.

Probability of Protection	Antibody Titers Level (U/ml) (95%CI)
50%	14.7 (8.6,25.0)
60%	27.8 (15.5,49.9)
70%	55.7 (28.8,107.8)
80%	129.0 (60.9,273.1)
90%	459.4 (184.9,1141.4)

CI, confidence interval.