Vaccines, Vol. 11, Pages 1419: Pleiotropic Effects of Influenza Vaccination

Vaccines, Vol. 11, Pages 1419: Pleiotropic Effects of Influenza Vaccination

Vaccines doi: 10.3390/vaccines11091419

Authors: Astrid Johannesson Hjelholt Cecilia Bergh Deepak L. Bhatt Ole Fröbert Mads Fuglsang Kjolby

Influenza vaccines are designed to mimic natural influenza virus exposure and stimulate a long-lasting immune response to future infections. The evolving nature of the influenza virus makes vaccination an important and efficacious strategy to reduce healthcare-related complications of influenza. Several lines of evidence indicate that influenza vaccination may induce nonspecific effects, also referred to as heterologous or pleiotropic effects, that go beyond protection against infection. Different explanations are proposed, including the upregulation and downregulation of cytokines and epigenetic reprogramming in monocytes and natural killer cells, imprinting an immunological memory in the innate immune system, a phenomenon termed “trained immunity”. Also, cross-reactivity between related stimuli and bystander activation, which entails activation of B and T lymphocytes without specific recognition of antigens, may play a role. In this review, we will discuss the possible nonspecific effects of influenza vaccination in cardiovascular disease, type 1 diabetes, cancer, and Alzheimer’s disease, future research questions, and potential implications. A discussion of the potential effects on infections by other pathogens is beyond the scope of this review.