Infectious diseases can trigger an autoimmune reaction through the mechanism of so-called “molecular mimicry”. Due to structural similarities between the surface molecules of a pathogen and protein components in the central or peripheral nervous system, there can in rare cases be a cross-reaction. Then, the immune system attacks not only the pathogen, but also the nerve tissue. If the brain is attacked, this can result in an acute brain inflammation – we then speak of an acute autoimmune encephalomyelitis (ADEM). Wild-type pathogens much more frequently lead to such unwanted cross-reactions, but fundamentally such a cross-reaction is also conceivable within the context of a vaccination. This is consistent with the historical reports on the early rabies vaccination, a disease that, incidentally, always leads to the patient’s death without vaccination. Here, the occasional occurrence of an acute autoimmune encephalomyelitis (ADEM) was observed. This was due to the (technically caused) contamination of the vaccine with animal nerve tissue – a problem that has long since been solved by modern vaccine development. However, this historical complication is still used as an argument by vaccine critics to claim that vaccines can trigger autoimmune diseases such as multiple sclerosis.
As far as the question is concerned whether vaccinations can cause MS, there is now scientific consensus that MS can neither be caused by inactivated vaccines nor by attenuated live vaccines. Case reports that postulate such a connection are only of limited value and have never been confirmed in larger case-control studies.
It is more difficult to answer the question whether vaccines are capable of triggering relapses in MS patients. This is conceivable with live vaccines, as they meet the criteria of an active infection with a replication-capable (albeit attenuated) organism. For example, there are indications that the yellow fever vaccine strain, which originates from a naturally occurring virus and has not completely lost its neurotoxicity even after numerous passages, can trigger relapses in MS patients, although the underlying sample size of this observation was relatively small.
Beyond these reports, however, there is no clear evidence that other live vaccines, such as measles, mumps and rubella (MMR), worsen MS – and for inactivated vaccines, no connection has ever been found between vaccination and disease activity. On the contrary, there is even rather evidence of lower disease activity in vaccinated patients. Even for vaccines that are often publicly associated with MS or the triggering of relapses, such as the vaccine against human papillomaviruses (HPV) or hepatitis B vaccines, there are no correlations between vaccination and clinical course. Vaccines have demonstrably more protection against infections or weaken them, thus providing an “indirect” protection against MS disease activity.
Accordingly, the vaccination protection of MS patients should be updated or completed according to the recommendations of the Standing Committee on Vaccination (STIKO). Inactivated vaccines (= dead vaccines) can generally be used in people with an autoimmune disease such as MS, regardless of whether they are being treated with an MS drug. Live vaccines can also be given to MS patients according to STIKO recommendations, but these should be administered before a planned immunotherapy.
