Vaccines have eradicated or controlled many
infectious diseases, saving each year millions of lives and quality of life of many other millions of people. In spite of the success of
vaccines over the last two centuries, parents (and also some health care workers) gloss over the devastating consequences of diseases, which are now avoided thanks to
vaccines, and direct their attention to possible negative effects of immunization. Three immunological objections are raised:
vaccines cause antigenic overload, natural immunity is safer and better than
vaccine-induced immunity, and
vaccines induce autoimmunity. The last point is examined in this review. Theoretically,
vaccines could trigger autoimmunity by means of
cytokine production, anti-idiotypic network, expression of human histocompatibility
leukocyte antigens, modification of
surface antigens and induction of novel
antigens, molecular mimicry, bystander activation,
epitope spreading, and polyclonal activation of B cells. There is strong evidence that none of these mechanisms is really effective in causing
autoimmune diseases.
Vaccines are not a source of
autoimmune diseases. By contrast, absolute evidence exists that infectious agents can trigger autoimmune mechanisms and that they do cause
autoimmune diseases.