Prevalence of and risk factors for long COVID following infection with the COVID‑19 omicron variant.

The aim of the present study was to clarify the current status of persistent symptoms following omicron variants of COVID-19 [long COVID (LC)] and the risk factors associated with the development of LC. For this purpose, a cross-sectional survey of patients with COVID-19 treated at the authors' hospital and at four associated outpatient clinics was conducted. Questionnaires about a post-infection condition were sent by post to 3,399 patients. A comparison was made of patients infected when the omicron variant was prevalent (omicron group) and patients infected prior to that (pre-omicron group). Valid responses were received from 1,113 (32.7%) patients. The percentages of patients in whom some type of symptom or sequelae continued after 1, 3 and 6 months were 44, 37 and 28%, respectively, in the pre-omicron group, and 20, 12 and 9%, respectively, in the omicron group. The percentages were significantly lower in the omicron group. In the multivariate analysis of risk factors for LC at 3 months, significant risk factors were hospitalization [odds ratio (OR), 1.910; P<0.01] and old age (OR, 1.120; P<0.05). Conversely, the incidence of LC was lower with vaccination (OR, 0.830; P<0.01) and in the omicron group (OR, 0.490; P<0.01). In the omicron group, underlying disease (particularly emphysema, bronchial asthma, rheumatoid or collagen disease and hypertension) and hospitalization were significantly associated with LC (P<0.01). On the whole, the present study demonstrates that the incidence of LC was >10% even in the omicron group. Patients who required hospitalization and patients with underlying conditions require careful attention for the development of LC.