Olfactory disorder after COVID-19 vaccination

This systematic review examines 16 reported cases of olfactory disorders occurring after COVID-19 vaccination. Symptoms such as anosmia, parosmia, hyposmia, ageusia, and dysgeusia appeared within one week of vaccination. Among the 16 patients (12 women, 4 men; mean age 38 years), 9 received the Pfizer mRNA vaccine, 6 received the AstraZeneca viral vector vaccine, and 1 received the Moderna mRNA vaccine. Symptoms persisted from 4 days to 18 months, with varying degrees of severity. Diagnoses were made using Sniffin' Sticks tests and T&T olfactometry, mosty revealing mild hyposmia. Treatment included vitamin B12, multivitamins, olfactory training, Kampo formula, and, in some cases, corticosteroids. The hypothesized mechanism involves inflammatory responses triggered by spike protein interaction with the alpha7 nicotinic acetylcholine receptor on macrophages. Given the lack of definitive diagnostic methods, careful clinical evaluation is essential to rule out other causes such as subclinical COVID-19 infection. While olfactory disorders have been reported after vaccination, no direct causal relationship has been established. Further research is needed to clarify underlying mechanisms and contributing factors.