Neurological complications of immunizations have been recorded in the medical literature for many years,
                   yet many physicians fail to recognize their clinical manifestations and identify their etiology. This is due in
                   part to their rarity, and to the well-publicized, overriding public health benefits that make these complications
                   easily overlooked. Yet they can be devastating despite the fact that early treatment is often successful. 

                   A great deal of knowledge regarding their pathogenesis has accumulated over the years based on the
                   existence of excellent animal models of the human disease, acute disseminated encephalomyelitis, the
                   commonest neurological manifestation of an adverse immune response to vaccines. Experimental allergic
                   encephalomyelitis and neuritis faithfully reproduce the pathologic alterations of the nervous system that may
                   complicate immunizations. 

                   Adverse reactions involving the nervous system from a wide variety of immunizations result from the same
                   pathogenetic mechanism. They may affect any and all parts of the central and peripheral nervous systems.
                   With rare exceptions, e.g. rubella immunization, the nature of the vaccine does not seem to influence the
                   nature of the response. 

                   Thus the nervous system ailments include many different clinical forms, ranging from the classic acute
                   disseminated encephalomyelitis to aseptic meningoencephalitis. In rare instances, in the case of live viruses,
                   e.g. polio and smallpox, an actual infection by the virus itself may ensue. Many different vaccinations
                   involving many different sites in the nervous system have been reported. This is particularly true of vaccines
                   commonly used in children against measles, varicella and rubella.

                   The pathogenetic mechanism is as follows: the primary effect of the hyperergic (immune) reaction is on the
                   small blood vessels of the nervous system, usually capillaries, but occasionally involving arterioles and
                   venules; in exceptional circumstances, even major arteries such as the carotid may be affected. The
                   vasculopathy may cause vessel obstruction and ischemia, a stroke. Rupture of the vessel wall results in
                   hemorrhage. 

                   More commonly, however, there is alteration of the blood-brain barrier, exsudation of water and edema
                   (swelling) of nervous tissue. Inflammation and disorganization of the myelin lamellae (layers) and destruction
                   of myelin may ensue but are not obligatory. In some cases, there is sufficient red blood cell diapedesis
                   (migration through the vessel wall) to produce what is known as acute hemorrhagic leukoencephalopathy,
                   which despite its awesome appearance is usually responsive to vigorous treatment. 

                   The extent of pathological involvement of nervous tissue also varies greatly, as seen in vaccination against
                   measles, mumps and varicella. In infants, brain swelling, also known as congestive edematous
                   encephalopathy, may be the only complication, a condition that often responds dramatically to treatment
                   with corticosteroids. It occurs most commonly in vaccination against smallpox.

                   The diagnosis of acute disseminated encephalomyelitis, the commonest complication of vaccinations in both
                   children and adult, has been aided by magnetic resonance imaging (MRI). The pictures are reasonably
                   characteristic, yet, unfortunately, despite many published descriptions, these images are not always
                   correctly interpreted, and are often misread as those of multiple sclerosis. 

                   There is also some confusion in terminology: “encephalitis” and “meningoencephalitis” refer to actual
                   invasion of the brain by a virus, while “encephalopathy” is a generic term that simply describes a
                   pathological condition of the brain; “encephalomyelitis” refers to an “allergic” or immune reaction of the
                   nervous system. It is the latter term that should be generally used for the nervous system complications of
                   vaccinations.

                   The official publications that commented on the ill effects of the 1976 swine-flu (A-New Jersey 76)
                   vaccination campaign illustrate the problems that arise when there is need to extrapolate scientific data to
                   judicial considerations. The report stating that the Landry-Guillain-Barré syndrome (LGBS) was the only
                   “real” complication of the swine-flu vaccine passed over published reports to the contrary. The statement
                   that there had been underreporting of complications was simply ignored. The accepted view is that if an
                   adverse reaction does not reach the magical figure of 5 percent, it does not exist.

                   The reverence accorded to statistical analyses overlooks the value of anecdotal reports in constructing valid
                   medical hypotheses; this is despite the warnings by respected epidemiologists that such studies can never
                   deny the existence of a cause-and-effect relationship. This is illustrated by the report of nervous system
                   complications following vaccination against hepatitis B. Another problem arose from the decision to limit the
                   “acceptable” time period of onset after immunization, which ignored a number of reports of
                   well-documented delayed reactions. 

                   In the last few years a new mantra has emerged to the effect that all published results such as proposed
                   new treatments, must meet the test of being “evidence-based,” which means that they must be derived
                   from statistically verified data. Thus calculations of probabilities, also known as educated guesses, will take
                   precedence over clinical, pathological, radiological or experimental data. Close examination of some specific
                   situations will reveal the flaws of this concept.

                   There is no way of predicting who will have an adverse reaction to vaccination. The individual’s susceptibility
                   is determined by the genetic background and previous immunological history. We are constantly exposed to
                   a wide variety of viral antigens that cause our immune system to develop antibodies against them. The
                   phenomenon of molecular mimicry explains why some people’s immune system will mistakenly respond to
                   the measles antigen, for instance, in the vaccine because some of its amino acid groupings, its epitopes,
                   are the same as those in the protein of a previously encountered viral antigen.

                   This is why there was an unexpected preponderance of people in their 50s and 60s who developed LGBS
                   after swine-flu vaccination, because they might have been exposed to the “Asian flu” caused by a somewhat
                   similar virus in the 1920s. It is also germane to point out that vaccines contain a number of substances,
                   many of them as antigenic as the one for which they were designed. Preservatives may also contribute to
                   the adverse side effects. It is extremely difficult to distinguish the effects of the vaccines’ constituents.

                   Physicians often neglect to ask about previous vaccinations when confronted with puzzling neurological
                   illness. Most of them appear to have been convinced that immunizations are completely harmless. Many
                   also believe that such reactions must occur within one month from vaccination, and therefore do not inquire
                   about immunizations in previous months.

                   Because of the expense of testing drugs, vaccines and other medical products, the pharmaceutical industry
                   has assumed an increasingly important role in the conduct of therapeutic trials and post-marketing
                   surveillance. This is both understandable and often beneficial. On the downside, however, is the
                   appearance of conflict of interest when the analyses of the results are carried out by the pharmaceutical
                   firm itself, or the government agency charged with guarding the safety of the product.

                   Dr. Poser is visiting professor of neurology, Department of Neurology, Harvard Medical School, Boston, and is senior neurologist with
                   Beth Israel Deaconess Med Center in Boston.

[Copyright 2003 by the author. First printed in Mealey's Litigation Report, Thimerosal & Vaccines, Volume 1, Issue #10, April 2003. This document sourced from Mercola.com.]