ReviewThe Lancet. Neurology2021
Post-viral effects of COVID-19 in the olfactory system and their implications.
Review in The Lancet. Neurology, 2021. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 107 papers, 4 of them syntheses that pooled it.
What it found
Each row is one number read from the abstract, on the scale the paper reported it, with its interval. Left of the dashed line favours the treatment, right favours the comparator. Under each row is the sentence it came from. New to these charts? A ten-minute tutorial.
The abstract states no effect estimate the extractor could read, or names no intervention and outcome on the map, so this paper lights no cell and moves no belief. It is still indexed, cited and linked below.
The trial behind it
Trials whose registry record cites this paper, or whose number appears in the abstract. A trial that started after this paper was published is citing it as background, not reporting it.
Neither the registry nor the abstract names a trial number. If this is a trial report, that itself is worth knowing.
Who cites it
107 citing papers in PubMed, 4 syntheses or guidelines pooled it, 184 citations in OpenAlex.
- Neurobiological mechanisms of olfactory dysfunction: a ten-year bibliometric and visualization analysis.Frontiers in medicine · 2026Pooled it
- Alzheimer's early detection in post-acute COVID-19 syndrome: a systematic review and expert consensus on preclinical assessments.Frontiers in aging neuroscience · 2023Pooled it
- Seroconversion rate after COVID-19 vaccination in patients with solid cancer: A systematic review and meta-analysis.Human vaccines & immunotherapeutics · 2022Pooled it
- Prognosis and persistence of smell and taste dysfunction in patients with covid-19: meta-analysis with parametric cure modelling of recovery curves.BMJ (Clinical research ed.) · 2022Pooled it
- Persistent COVID-19 parosmia and olfactory loss post olfactory training: randomized clinical trial comparing central and peripheral-acting therapeutics.European archives of oto-rhino-laryngology : official journal of the European Federation of Oto-Rhino-Laryngological Societies (EUFOS) : affiliated with the German Society for Oto-Rhino-Laryngology - Head and Neck Surgery · 2024Trial
- Treatment of COVID-19 olfactory dysfunction with olfactory training, palmitoylethanolamide with luteolin, or combined therapy: a blinded controlled multicenter randomized trial.European archives of oto-rhino-laryngology : official journal of the European Federation of Oto-Rhino-Laryngological Societies (EUFOS) : affiliated with the German Society for Oto-Rhino-Laryngology - Head and Neck Surgery · 2023Trial
- Ultramicronized Palmitoylethanolamide and Luteolin Supplement Combined with Olfactory Training to Treat Post-COVID-19 Olfactory Impairment: A Multi-Center Double-Blinded Randomized Placebo- Controlled Clinical Trial.Current neuropharmacology · 2022Trial
- Cognitive assessment of patients with post-COVID olfactory dysfunction and impaired domains.Neurological sciences : official journal of the Italian Neurological Society and of the Italian Society of Clinical Neurophysiology · 2026Article
- The Unmet Need of Olfactory Testing in Inflammatory Disorders of the Upper Airways-An EAACI Position Paper.Allergy · 2026Review
- Therapeutic Effects and Mechanisms of Olfactory Training in a Murine Model of Olfactory Dysfunction.Otolaryngology--head and neck surgery : official journal of American Academy of Otolaryngology-Head and Neck Surgery · 2026Article
- Effect of intranasal vitamin A nanoparticles on persistent olfactory dysfunction: a randomized clinical trial.European archives of oto-rhino-laryngology : official journal of the European Federation of Oto-Rhino-Laryngological Societies (EUFOS) : affiliated with the German Society for Oto-Rhino-Laryngology - Head and Neck Surgery · 2026Article
- Longitudinal evaluation of neurocognitive outcomes in a cohort with persistent post-COVID olfactory dysfunction.Scientific reports · 2026Article
- SARS-CoV-2 Spike Protein Induces Time-Dependent and Brain-Region-Specific Alterations in Ferroptosis Markers: A Preliminary Study in K18-hACE2 Mice.International journal of molecular sciences · 2026Article
- Review
- Combination antiviral and anti-inflammatory therapy mitigates persistent neurological deficits in mice post SARS-CoV-2 infection.Proceedings of the National Academy of Sciences of the United States of America · 2026Article
- Neuroimaging and Transcriptomic Insights Into Iron Accumulation and Glymphatic Dysfunction in Olfactory Dysfunction.CNS neuroscience & therapeutics · 2026Article
- Insight into NeuroCOVID: neurofilament light chain (NfL) as a biomarker in post-COVID-19 patients with olfactory dysfunctions.Journal of neurology · 2025Article
- Viral Etiologies and Histopathological Features of Olfactory Dysfunction: A Systematic Review.Health science reports · 2025Review
- Anosmia predicts memory impairment in post-COVID-19 syndrome: results of a neuropsychological cohort study.European archives of psychiatry and clinical neuroscience · 2025Article
- IFN-bioRxiv : the preprint server for biology · 2025Article
47 more citing papers are in PubMed but not listed here.
Corrections and comments
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Authors and funding
10 authors at 8 institutions in 3 countries.
Funding
No grant is acknowledged in the PubMed record.
Abstract
backgroundThe mechanisms by which any upper respiratory virus, including SARS-CoV-2, impairs chemosensory function are not known. COVID-19 is frequently associated with olfactory dysfunction after viral infection, which provides a research opportunity to evaluate the natural course of this neurological finding. Clinical trials and prospective and histological studies of new-onset post-viral olfactory dysfunction have been limited by small sample sizes and a paucity of advanced neuroimaging data and neuropathological samples. Although data from neuropathological specimens are now available, neuroimaging of the olfactory system during the acute phase of infection is still rare due to infection control concerns and critical illness and represents a substantial gap in knowledge. RECENT DEVELOPMENTS: The active replication of SARS-CoV-2 within the brain parenchyma (ie, in neurons and glia) has not been proven. Nevertheless, post-viral olfactory dysfunction can be viewed as a focal neurological deficit in patients with COVID-19. Evidence is also sparse for a direct causal relation between SARS-CoV-2 infection and abnormal brain findings at autopsy, and for trans-synaptic spread of the virus from the olfactory epithelium to the olfactory bulb. Taken together, clinical, radiological, histological, ultrastructural, and molecular data implicate inflammation, with or without infection, in either the olfactory epithelium, the olfactory bulb, or both. This inflammation leads to persistent olfactory deficits in a subset of people who have recovered from COVID-19. Neuroimaging has revealed localised inflammation in intracranial olfactory structures. To date, histopathological, ultrastructural, and molecular evidence does not suggest that SARS-CoV-2 is an obligate neuropathogen. WHERE NEXT?: The prevalence of CNS and olfactory bulb pathosis in patients with COVID-19 is not known. We postulate that, in people who have recovered from COVID-19, a chronic, recrudescent, or permanent olfactory deficit could be prognostic for an increased likelihood of neurological sequelae or neurodegenerative disorders in the long term. An inflammatory stimulus from the nasal olfactory epithelium to the olfactory bulbs and connected brain regions might accelerate pathological processes and symptomatic progression of neurodegenerative disease. Persistent olfactory impairment with or without perceptual distortions (ie, parosmias or phantosmias) after SARS-CoV-2 infection could, therefore, serve as a marker to identify people with an increased long-term risk of neurological disease.
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Read under generation 80e0d062 · epoch 390. Bibliography from PubMed, PubMed Central and OpenAlex; grants from NIH RePORTER; trial links from ClinicalTrials.gov; estimates, votes and beliefs from the OpenQuestion graph.