These complications are caused by an allergic reaction to the myelin of the brain tissue contained in the vaccine. Pathologically developing complication is regarded as disseminated, sometimes diffuse, encephalomyelitis and polyneuritis with a slight meningeal reaction. Mostly gray matter suffers. In peripheral nerves, as in the brain, vascular changes prevail over degenerative ones. The first signs of complication usually appear after the initial sessions, more often after the 4-8th injection of the rabies vaccine. The prodromal period occurs in the form of dizziness, general weakness, nausea or diarrhea, pain at the injection site and throughout the body. Then the temperature rises, there is a headache, stupor , vomiting, often indomitable.
The pupils are initially wide, then become narrow, strabismus often occurs. The facial nerve is sometimes involved. Bulbar phenomena are possible: impaired swallowing, increased heart rate and breathing. The picture of simultaneous damage to the peripheral nerves and spinal cord unfolds and progresses within 2-6 days. Flaccid paralysis of the legs or arms develops, sphincter disturbances and less often sensory disturbances along the conductor or polyneuritic type appear. In areas of impaired innervation of limbs, tissues are painful to the touch. In the cerebrospinal fluid are often found high protein and small pleopitosis with a predominance of lymphocytes. The regression of symptoms of encephalomyeloradiculoneuritis begins quickly – as is usually the case with allergic processes and only in isolated observations lasts for months with the preservation of residual paresis and sensitivity disorders. The severity and prevalence of the process varies from fulminant ascending paralysis, ending in 1/3 of the cases fatally, to abortive mononeuritis.