Table 3.

Comparison of PRNT Titers Using Different Plaquing Viruses at Day 30 After Vaccination in a Subset of Dryvax and LC16m8 Volunteers Tested at All Laboratories

PRNT assay virus	Dryvax	LC16m8	Dryvax/LC16m8 ratio	P value
Number of titers	23	26	…
Anti-Dryvax (Focus)
Geometric mean	919	329	2.8	<.001
95% CI	565–1493	228–474	1.6–5.0
Anti-LC16m8 (KKT)
Geometric mean	471	733	0.6	.24
95% CI	301–739	400–1343	.3–1.4
Anti-Lister (KKT)
Geometric mean	7686	17 523	0.4	.09
95% CI	3687–16 026	9104–33 725	.2–1.1
Anti-monkeypox (JNIID)
Geometric mean	368	112	3.3	<.001
95% CI	225–597	82–307	1.7–6.3
Anti-NYCBH (JNIID)
Geometric mean	482	158	3.0	.01
95% CI	287–810	82–307	1.3–7.0
Anti-Lister (JNIID)
Geometric mean	298	207	1.4	.29
95% CI	176–504	129–332	.7–2.9

Per protocol cohort excludes 4 volunteers who had anti-Dryvax PRNT (Focus) titers ≥40 at baseline and 2 volunteers who had missing anti-Dryvax PRNT (Focus) titer data at day 30. Plaque viruses included Dryvax (NYCBH–vaccine-derived virus), NYCBH (Japan vaccine–derived seed), Lister, LC16m8, and monkeypox. PRNT tests were performed at 3 different laboratories: anti-Dryvax assay at Focus, Inc; anti-NYCBH at JNIID (Tokyo, Japan); anti-Lister vaccinia at both JNIID and KKT (Kumamoto, Japan); anti-LC16m8 vaccinia at KKT; and the antimonkeypox at JNIID. These assays were performed on sera obtained on day 30 after vaccination. P values were calculated using Wilcoxon rank-sum test.

Abbreviations: CI, confidence interval; JNIID, Japanese National Institute of Infectious Diseases; KKT, Kaketsuken; NYCBH, New York City Board of Health; PRNT, plaque reduction neutralization titers.