Eosinophils were discovered more than 140 years ago. This polymorphonuclear leukocyte has a very active metabolism, containing numerous intracellular secretory granules that allow it exerts multiple functions in both health and disease status.
Classically, eosinophils have been considered as important immune cells in the pathogenesis of inflammatory processes such as parasitic helminth infections and allergic or pulmonary diseases like asthma, being always associated to a type 2 immune response; furthermore, in the last years, it has been linked to immune response conferring host protection against fungi, bacteria, and viruses, recognizing them through several molecules such as toll-like receptors (TLRs) or retinoic acid-inducible gene 1 (RIG-1)-like receptor (RLR).
The immune protection is exerted through multiple mechanisms and properties of these cells. They contain numerous cytoplasmatic granules that release cationic proteins, cytokines, chemokines and other molecules that contribute to their functions.
In addition to their competence as effectors cells, its capabilities like antigen-presenting cell allow them to act in multiple situations promoting diverse aspects of the immune response.
This review summarizes diverse aspects of eosinophil biology and mainly, it goes over the mechanisms and roles carried out by eosinophils in host defence against virus infections and vaccines response, focusing the attention in respiratory viruses like the new coronavirus, SARS-CoV-2.

Key words: Eosinophils, Respiratory viruses, Immune response, Vaccines, Emerging viruses