Mucosal antibody response and SARS-CoV-2 shedding in patients with COVID-19 related olfactory dysfunction

Olfactory dysfunction (OD) was one of the most common symptom of infection with the Wuhan strain of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and could persist for several months after symptom onset. The pathogenesis of prolonged OD remains poorly understood but probably involves sustained viral replication associated with limited mucosal immune response to the virus. This prospective study was conducted to investigate the potential relationship between nasal SARS-CoV-2 viral load and antibody levels in patients with loss of smell. One hundred and five patients were recruited 2 weeks after presenting with confirmed coronavirus disease 2019 associated OD. Based on the identification sniffing test performed at enrollment, 52 patients were still anosmic or hyposmic and 53 were normosmic. SARS-CoV-2 was detectable in nasal wash of about 50% of anosmic and normosmic patients. Higher viral load was detected in anosmic patients with lower levels of SARS-CoV-2 specific nasal immunoglobulins (Ig) IgG and IgA. This association was not observed in normosmic patients. No relationship between nasal viral load and antibodies to endemic coronaviruses was observed. SARS-CoV-2 replication in the nasal cavity may be promoted by defective mucosal antibody responses in patients with OD. Boosting mucosal immunity may limit nasal SARS-CoV-2 replication and thereby help in the control of persistent OD.