INTRODUCTION
During the first wave of the COVID-19 pandemic, olfactory dysfunction (OD) was one of the most common (50-85%) and long-lasting symptoms of COVID-19 patients1,2. Between 5-10% of patients, presented a persistent OD beyond a year after onset3. Long-term OD appears to be related to the destruction of the neuroepithelium but the mechanisms underlying this destruction remain poorly understood4,5. Persistence of SARS-CoV-2 replication in the neuroepithelium, potentially promoted by defective mucosal immunity, may be involved6. We previously reported lower nasal and salivary IgG levels in patients with persistent anosmia as compared to patients with more transient symptoms7. On the other hand, studies indicated that OD is associated with increasing levels of serum antibodies in the first month following onset of symptoms, suggesting persistent antigen stimulation8. Together, these data suggest a complex interaction between viral replication and antibody response when viral replication in the nasal cavity may be promoted by low antibody responses and may in turn stimulate antibody production over prolonged periods of time9. More insights are needed on the relationship between viral replication and mucosal antibody response to decipher their potentially complex interactions in patients with COVID-19 OD10.
A potentially important determinant of adaptive immune responses to SARS-CoV-2 is pre-existing immunity to endemic coronaviruses, including HKU1, OC43, 229E and NL63, to which patients have been commonly exposed. Studies suggest that pre-existing immunity to endemic coronaviruses may reduce the severity of COVID-1911. Whether an impact on SARS-CoV-2 replication in the nasal cavity can also be observed is currently unknown. This prospective study was conducted to investigate the potential relationship between nasal SARS-CoV-2 viral load and antibody levels in patients with OD.