Lost and Found: Is Olfactory Recovery More Promising After COVID-19 Than Other Causes, Even 2 Years Later?

BACKGROUND

Olfactory dysfunction is a hallmark feature of COVID-19, yet the potential for recovery with long-standing COVID-19-related smell loss (CRSL) remains uncertain, particularly when treatment is initiated years later. This study evaluated olfactory outcomes in patients with CRSL compared with non-COVID-19-related smell loss (non-CRSL), with emphasis on delayed treatment initiation.

METHODS

This retrospective cohort study included 104 patients evaluated at a tertiary clinic between January 2023 and February 2025, comprising 47 patients with CRSL and 57 with non-CRSL. All patients completed serial Sniffin' Sticks testing (threshold, discrimination, and identification [TDI]) at ≥2 visits. Minimal clinically important difference (MCID) was defined as a ≥5.5-point increase in TDI score. All patients received olfactory training combined with twice-daily steroid nasal irrigation. Subgroup analyses examined delayed treatment initiation (>2 years), treatment adherence, and COVID-19 vaccination status.

RESULTS

Baseline TDI scores were higher in the CRSL group than in the non-CRSL group (19.6 ± 6.3 vs. 16.8 ± 6.8; p < 0.05). The CRSL group demonstrated significant improvement in TDI scores at follow-up (19.6 ± 6.3 to 23.9 ± 6.5; p < 0.001), with 46% achieving MCID, whereas the non-CRSL group showed no significant change. Among CRSL patients initiating therapy >2 years after onset (n = 36; mean 30.8 ± 5.5 months), 50% achieved MCID. Treatment adherence was strongly associated with improvement, whereas COVID-19 vaccination showed a favorable but attenuated association after adjustment.

CONCLUSIONS

Clinically meaningful olfactory recovery remains achievable with long-standing CRSL, even when treatment is initiated >2 years after onset. Prospective studies are needed to clarify causal relationships given known spontaneous recovery in post-viral olfactory dysfunction.