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.

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