Effects of Gamma Irradiation of Human Serum Samples from rVSVΔG-ZEBOV-GP (V920) Ebola Virus Vaccine Recipients on Plaque-Reduction Neutralization Assays

Abstract

Gamma irradiation (GI) is included in the CDC guidance on inactivation procedures to render a group of select agents and toxins nonviable. The Ebola virus falls within this group because it potentially poses a severe threat to public health and safety. To evaluate the impact of GI at a target dose of 50 kGy on neutralizing antibody titers induced by the rVSVΔG-ZEBOV-GP vaccine (V920), we constructed a panel of 48 paired human serum samples (GI-treated versus non-GI-treated) from healthy participants selected from a phase 3 study of V920 (study V920-012; NCT02503202). Neutralizing antibody titers were determined using a validated plaque-reduction neutralization test. GI of sera from V920 recipients was associated with approximately 20% reduction in postvaccination neutralizing antibody titers. GI was not associated with any change in pre-vaccination neutralizing antibody titers.

Conflict of interest statement

Disclosure: R. J. G.-K., J. A., S. D., and J. K. S. are employees of Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, and may own stock/stock options in Merck & Co., Inc., Kenilworth, NJ. R. N. has received personal fees from New Link Genetics as a consultant.

Figures

Figure 1.

Concordance plot displaying the effect of GI on neutralizing antibody titer of human clinical samples from vaccinated subjects as measured in the V920 PRNT. aFor ease of data visualization, pre-vaccination samples (titers < 20), which were excluded from the analyses, were randomly assigned a titer close to 10. GI = gamma irradiation; LOD = limit of detection; PRNT = plaque-reduction neutralization test; rVSVΔG-ZEBOV-GP = recombinant vesicular stomatitis virus–Zaire Ebola virus envelope glycoprotein; V920 = rVSVΔG-ZEBOV-GP vaccine.