system damage several years prior to the appearance of symptoms that present at time of diagnosis (Stone, 1995). The only factor shown definitively to trigger exacerbations of MS is an acute viral infection. MS patients who have acute viral infections are at greater risk for an exacerbation than those who are not infected (Sibley, 1997). Several studies have found that vaccination does not increase the risk for an exacerbation of MS (Miller et al., 1997). One study using MRI found there was no evidence of increased nerve damage in MS patients after vaccination against influenza virus (Ropper, 1992).

Another autoimmune disorder, GBS, causes progressive paralysis due to a loss of myelin around nerves. A majority of GBS patients report some kind of ''trigger" event (infections, surgery) shortly before the onset of GBS (Ropper, 1992). Studies of swine influenza vaccine recipients indicated that they had approximately 8 fold increase risk of GBS during the weeks immediately post-vaccination compared to nonrecipients (Schonberger et al., 1979; Safranek et al., 1991). It is not clear whether a contaminant or the virus itself in these batches made people more susceptible to GBS. Subsequent influenza vaccines prepared from other virus strains have not been clearly associated with an increases risk of GBS (Hurwitz et al., 1981; Kaplan et al., 1982; Chen et al., 1992). During five of six seasons studied since 1976, the point estimates of the relative risks of GBS after influenza vaccination were slightly elevated; however, in none of these studies was the overall elevation in relative risk statistically significant (CDC, 1997). This may be due to either a low barely detectable risk or by uncontrolled confounding or bias. Another study found that those individuals who reported experiencing GBS following vaccination against swine flu were not more likely than those without the syndrome to have a family or personal history of autoimmune disorders (Ropper, 1992).

Some people have expressed concern that individuals vaccinated for several diseases simultaneously might be at increased risk for experiencing adverse effects, such as abnormal immune system responses (Peeler et al., 1958; Peeler et al., 1965; White et al., 1974). Although people are constantly exposed to multiple antigens, the presentation (injection into skin or muscle, for example) of vaccine antigens is different from the way common antigens, such as food or naturally-occurring viruses and bacteria, are encountered. Many employees at the USA Medical Research Institute of Infectious Diseases at Fort Detrick in Frederick, Maryland, receive multiple vaccinations to protect them from the