Olfactory Dysfunction and Hallucinations Following Vaccination

 A 39-year-old veteran, with a history of tension-type headaches, noticed a burning odor sensation approximately three weeks after receiving the J&J COVID-19 vaccine, about four months prior to his visit to the neurology clinic. Concerned about this peculiar symptom, he underwent a nasal swab antigen COVID-19 test, which returned negative. Initially, the episodes occurred daily, lasting about one hour each time. However, as time passed, they became less frequent, shorter in duration, and less intense. About 11 months post-vaccination, milder episodes occurred only 1 to 2 times weekly. These olfactory hallucinations persisted for nearly two years (21 months post-vaccination), occurring randomly throughout the day and unrelated to any other symptoms. 

When the veteran presented to the clinic, both general and neurological examinations yielded unremarkable results. Brain magnetic resonance imaging (MRI) did reveal chronic sinusitis but showed no other abnormalities. It's important to note that the phantosmia persisted even after the sinusitis had been treated with doxycycline. Additionally, an electroencephalogram (EEG) was obtained, which also appeared normal, although it did not capture the episodes of phantosmia.

Thousands of cases of vaccination affecting the sense of smell were reported in VAERS database, but only a few are described in medical literature. 

Phantosmia, featured by a burning or smoke odor, has been reported prior in a case of a 57-year-old woman following the administration of the Pfizer-BioNTech mRNA vaccine.  Concurrent COVID-19 infection was also ruled out via a COVID-19 polymerase chain reaction test. While the Pfizer-BioNTech phantosmia case showed abnormalities in brain MRI scans, the J&J COVID-19 vaccine case displayed no such findings. 

In addition to phantosmia, hyposmia (reduced sense of smell) has been reported following Pfizer-BioNTech COVID-19 vaccination in two cases. Both patients, females aged 39 and 42, experienced hyposmia following their second vaccine dose, with varying degrees of symptom improvement over time.



REFERENCES

Barter K, Bagnato F. Olfactory Hallucinations Following COVID-19 Vaccination. Fed Pract. 2023 Sep;40(9):1-3. doi: 10.12788/fp.0410. Epub 2023 Sep 12. PMID: 37727678; PMCID: PMC10506491.

Keir G, Maria NI, Kirsch CFE. Unique imaging findings of neurologic phantosmia following Pfizer-BioNtech COVID-19 vaccination: a case report. Top Magn Reson Imaging. 2021;30(3):133–137. doi: 10.1097/RMR.0000000000000287. 

Konstantinidis I, Tsakiropoulou E, Hähner A, de With K, Poulas K, Hummel T. Olfactory dysfunction after coronavirus disease 2019 (COVID-19) vaccination. Int Forum Allergy Rhinol. 2021;11(9):1399–1401. doi: 10.1002/alr.22809


https://medalerts.org/vaersdb/findfield.php?IDNUMBER=2285342

https://medalerts.org/vaersdb/findfield.php?IDNUMBER=2313333

https://medalerts.org/vaersdb/findfield.php?IDNUMBER=2680345

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