Table 2. Midpoint Titers and IC₅₀ Values by ELISA and SPR, Respectively.

		midpoint titersa			IC50b (nM)
vaccination group	antigen	week 3	week 5	analyte	week 3	week 5
Fent	Her-BSA	175 ± 87	509 ± 154	6-AMc
	Fent-BSA	541 ± 80‡‡	4614 ± 1186‡	fentanyl	344 (232–511)	71 (60–84)
Her	Her-BSA	3378 ± 1543	4732 ± 714	6-AMd	121 (105–139)	46 (43–50)
	Fent-BSA	49 ± 10	28 ± 6	fentanylc
Fent + Her	Her-BSA	12 903 ± 1918****	18 483 ± 3129****	6-AMd	201 (149–289)	76 (48–121)
	Fent-BSA	1380 ± 171‡‡‡‡	10 098 ± 1661‡‡‡‡	fentanyl	124 (59–259)	77 (47–126)
control	Her-BSA	23 ± 4	14 ± 7	6-AMd	n.d.e	n.d.e
	Fent-BSA	45 ± 7	11 ± 3	fentanyl	n.d.e	n.d.e

^aMidpoint titers are reported as means ± standard error of the mean.

^bIC₅₀ values are reported as means, and 95% confidence intervals are given in parentheses in nanomolar.

^c6-AM and fentanyl were not run for Fent-TT and Her-TT vaccination groups, respectively.

^d6-AM was the primary analyte used in the SPR studies because of its longer half-life at pH 7.4 at room temperature compared to heroin.

^eControl vaccine groups were run by SPR but did not converge because of lack of detected antibody binding. Significance is denoted by an asterisk (for Her-BSA as the coating antigen) or double dagger (for Fent-BSA as the coating antigen) for midpoint titer from a one-way ANOVA and a Dunnett’s post hoc test when comparing vaccinated groups to controls. ***P ≤ 0.001; *P < 0.05; ‡‡‡P ≤ 0.001 vs control.