Efficacy of herpes vaccine in a rabbit model following intraocular inoculation of herpes simplex virus.

It has been shown that injection of herpes simplex virus type 1 into the vitreous body of the eye in 18-day-old albino rabbits consistently induced encephalitis caused by herpes simplex virus, with 95% survival. In untreated rabbits the lesions followed a defined anatomic pathway in the central nervous system, and produced a chronic progressive disease with gross pathological features very similar to those seen in the natural human disease. The efficacy of heat-killed herpes vaccine in this animal model was studied by starting immunization four days before or four days after the live challenge. All animals immunized before the challenge were protected. Immunization after the challenge not only did not confer protection, but surprisingly, appeared to enhance the primary disease. The rabbits immunized after the challenge developed weakness of the hind legs that progressed very rapidly to paralysis, and an appreciable proportion (40%) of them died between days 18 and 23 postvaccination.