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. 2025 Jan 24;5(2):17.
doi: 10.3892/mi.2025.216. eCollection 2025 Mar-Apr.

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

Isao Moritani  1 , Kenji Yamanaka  2 , Tai Nakamura  3 , Junichiro Tanaka  4 , Keigo Kainuma  5 , Masakazu Okamoto  6 , Tomoko Ieki  7 , Hideo Wada  7 , Katsuya Shiraki  7
Affiliations

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

Isao Moritani et al. Med Int (Lond). .

Abstract

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.

Keywords: COVID-19; long COVID; omicron variant.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1
Flow diagram of the screening process used for the patients with COVID-19 in the present study.
Figure 2
Figure 2
Incidence of sequelae following COVID-19 infection in the pre-omicron and omicron groups. **P<0.01.
See this image and copyright information in PMC

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