While COVID-19 immunization improves olfactory ability, it is reported to cause hyposmia. This is described in two patients with the onset of hyposmia after the second dose of mRNA COVID-19 vaccination. However, exacerbation of hyposmia after each of three doses of COVID-19 vaccination has not heretofore been described. A primary immune mechanism has been suggested since the infection-induced olfactory loss is frequently seen in autoimmune diseases and those with antinuclear antibodies and olfactory loss. In addition, spike proteins appear after COVID-19 vaccination that may affect alpha seven nicotinic acetylcholine receptors, deregulating acetylcholine pathways and causing a release of proinflammatory cytokines.
