Olfactory disorders have a significant impact on human lives - be it a lost/distorted sense of smell or unpleasant odors affecting the sense of smell of others.
Odortypes can be influenced by human leukocyte antigen (HLA) genes of the major histocompatibility complex (MHC), genes associated with stronger response to COVID-19 vaccine as well as the severity of this disease. HLA may also be related to people's perception of the odor of other people. 
Of course, these are not the only variables involved, and there are more potentially overlapping risk factors for olfaction, metabolic body odor (MEBO), including trimethylaminuria (TMAU), and COVID-19: FMO3, SELENBP1, HspA, UGT2A1/UGT2A2, etc.
A new peer-reviewed paper reporting results of a decentralized observational study (NCT04832932) compared MEBO participants to general populations in respect to their response to COVID-19 vaccines and SARS-Co-V2 infections.
Body odor flareups were observed in about 10% of malodor sufferers after vaccination, as preliminarily reported. This number was similar to flareups of other chronic symptoms in groups of participants with gastrointestinal and autoimmune disorders.
Long-term worsening of body odor was observed by other researchers after COVID-19 vaccination in about ~1% of studied populations. Dry mouth leading to halitosis was 10 times more prevalent compared to flu vaccines. MEBO participants reported stronger reactions than general population pointing to genetic and microbiome influences beyond FMO3.
A better understanding of systemic malodor conditions could offer leads for targeted therapies. Findings on genetic and microbiome overlaps between COVID-19 and MEBO could pave the way for precision medicine to address the unmet needs of odor sufferers.
REFERENCE
Gabashvili IS. The Incidence and Effect of Adverse Events Due to COVID-19 Vaccines on Breakthrough Infections: Decentralized Observational Study With Underrepresented Groups. JMIR Formative Research. 2022 Nov;6(11):e41914. DOI: 10.2196/41914. PMID: 36309347; PMCID: PMC9640199.
