Neurological complications of immunization.

Vaccines prepared from whole, killed organisms (pertussis and possibly influenza) may cause neurological allergic reactions producing encephalopathy. These reactions are characterized by acute, monophasic demyelinative processes and occur with no greater frequency than 1 per 100,000 vaccine recipients; onset is within 4 days of immunization, and recovery is usually complete. No evidence suggests that these vaccines produce an insidious, progressive encephalopathy. Only with the swine influenza program of 1976 has Guillain-Barré syndrome appeared to follow immunization. Vaccines prepared from live-attenuated viruses (measles, mumps, rubella, and trivalent oral poliovirus) can cause symptomatic viral infection of the nervous system, including measles encephalitis, which occurs in 1 of 1,000,000 vaccine recipients; rubella neuritis, in less than 1 of 10,000 recipients; and paralytic poliomyelitis, in 1 of 3,000,000 vaccine recipients or their close contacts. A cause-and-effect relationship between immunization and brachial plexus neuritis, acute transverse myelitis, and cranial neuropathies has been suggested but never proved.