Covid-19 virus and symptoms, illustration. The upper third shows the structure of the coronavirus in cross-section. Beneath are the symptoms that a covid-19 infection may cause. From top to bottom these are: headache, fever, weakness, sore throat, loss of the sense of taste and smell, destruction of the alveoli, pneumonia and stomach trouble. The lower third shows a simplified description of a messenger RNA (mRNA) vaccine, which are given in the upper arm muscle. Lipid nanoparticles (LNPs) serve carriers that deliver the mRNA to the cell. Once in the cytoplasm, the mRNA instructs the cell's machinery to produce a harmless piece of the pathogen, which is displayed on the cells surface. The immune system then recognizes the unfamiliar protein and produces antibodies against it. These antibodies are then able to fight off a real infection.