Dr. William Halford at the Southern Illinois University (SIU) School of Medicine tested a live-attenuated HSV-2 ICP0∆NLS vaccine in 2016, before his death in June, 2017.[41][42][43] Vaccine attenuation is achieved by a mutation in ICP0 (ICP0∆NLS) that increases the vaccine strain's sensitivity to interferon responses and limits its replication. Already proven as safe and effective in rodents and eliciting 10 to 100 times greater protection against genital herpes than a glycoprotein D subunit vaccine, Halford's vaccine was tested outside of the United States, in St. Kitts in 20 human volunteers. All 20 of the participants self-reported an improvement in symptoms, but only 17 received and completed all three dosages.[44] Blot tests showed a clear antibody response, which cannot be instigated by a placebo effect.