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INNOSC Theranostics and
Pharmacological Sciences Persistent olfactory and gustatory dysfunctions caused by COVID-19 vaccination

Table 1. (Continued)
References Causative vaccine Onset after Manifestations Persistent Previous COVID‑19
vaccination manifestations and infection and course
duration
Keir et al. 11 Second dose of the Several days - A 57-year-old female Phantosmia and No
Pfizer’s vaccine - Constant phantosmia and hyposmia hyposmia
(smoke smell)
- MRI showed edema of olfactory bulbs
and tracts, clumping of olfactory nerve
filia (suggestive of inflammation)
- No history of parosmia or taste loss
Abbreviations: ESKD: End-stage kidney disease; GBS: Guillain–Barré Syndrome; IVIG: Intravenous immunoglobulins; MRI: Magnetic resonance
imaging.

was due to persistent hyposmia for 3 years. The SOIT score patients developed the disorders after the second dose
was 9 out of 16, indicating hyposmia. Both the flavor and of the vaccine. Studies have observed that inactivated
taste sensations remained intact. viral and viral vector-based vaccines induced a stronger
immune response after the second dose compared to the
3. Discussion weak cellular immune responses against spike protein after

In this study, three adult males were reported to have the first dose of the vaccine, which has been considered
developed smell and taste disorders between 9 and 20 days compatible with an antibody-dependent enhancement
15
after the second dose of the AstraZeneca vaccine was mechanism. (3) It has been suggested that the local
administered in 2021. Persistent disorders, including expression of the spike protein after vaccination and its
dysgeusia, anosmia, parosmia, and hyposmia, lasting interaction with the α7 nicotinic acetylcholine receptors
1 – 3 years were observed. A temporal relation between the in macrophages may cause deregulation of the cholinergic
vaccination and the development of the disorders, together pathway, release of proinflammatory cytokines, and
with repeatedly negative nasal swabs and PCR tests for activation of the inflammatory reflex. Signals could be
SARS-CoV-2 and the exclusion of alternative causes, produced and transmitted via neural pathways from the
(4) It has been
local injection site to the distant one.
16,17
further confirms that these disorders were adverse effects suggested that these disorders may be due to demyelination
of the vaccine. To date, only six case reports have been of the chemosensory nerves. Demyelination of the central
published describing persistent smell and taste disorders, and peripheral nervous systems may be triggered by the
which lasted more than 3 months to over 3 years following vaccines. (5) Reduction in olfactory bulb volume has
8,18
COVID-19 vaccination. These disorders included been suggested as a cause of persistent post-COVID-19
parosmia, hyposmia, dysgeusia, and phantosmia 6-11 vaccine anosmia/hyposmia. In support of this, a
7,19
(Table 1).
reduction in the volume of the olfactory bulbs has been
The pathogenic mechanisms of post-COVID-19 vaccine reported in patients with persistent post-COVID-19
smell and taste disorders have not yet been understood olfactory disorders. (6) Activation of COVID-19
20
and remain speculative. Some mechanisms have been infection by the vaccine in asymptomatic carriers has been
hypothesized: (1) It has been proposed that the vaccine recommended. However, this suggestion is not currently
may have similar effects to the attachment of SARS-CoV-2 applicable because all reported cases demonstrated negative
to the olfactory epithelium and perivascular angiotensin- repeated PCR and repeated nasal swabs for SARS-CoV-2
converting enzyme type 2 receptors, causing inflammation at the onset of the conditions, which ruled out COVID-19
of the olfactory neuroepithelium. This has been supported infection as a cause of smell and taste disorders.
by findings of olfactory edema, blocked olfactory clefts,
and clumping of olfactory filia in some patients with 4. Conclusion
post-vaccination anosmia. However, this mechanism Persistent smell and taste disorders may occur as
7,14
has not been considered applicable because most cases complications following post-COVID-19 vaccination.
had normal MRI at the acute condition. (2) It has been Reports of COVID-19 vaccine-related smell and taste
suggested that the humoral immune response triggered adverse effects should not be ignored and must be
by the spike protein induced by the mRNA vaccine may recognized by otolaryngologists and different medical
directly damage the olfactory neuroepithelium without specialties, including neurologists. These adverse effects
replication of the virus. It has been observed that most should also be considered in future studies on vaccine
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Volume 8 Issue 3 (2025) 104 doi: 10.36922/ITPS025140020