Understanding the Burden of Long COVID in the Omicron Era: A Prospective Observational Study in Thailand


The emergence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in late 2019 marked the beginning of an unprecedented global health crisis, the COVID-19 pandemic. Characterized by a wide spectrum of clinical manifestations, ranging from asymptomatic cases to severe pneumonia and multi-organ dysfunction, COVID-19 has profoundly impacted public health worldwide [1]. The virus primarily targets host cells expressing angiotensin-converting enzyme 2 (ACE-2) receptors, leading to systemic inflammation and organ dysfunction [2,3].

As of May 17, 2021, global COVID-19 cases surpassed 255 million, with over 2 million cases reported in Thailand alone [4]. A concerning trend observed among recovered patients is the development of chronic symptoms, commonly referred to as ‘Long COVID’ [5]. The World Health Organization defines Long COVID as the persistence or emergence of symptoms beyond 12 weeks post-SARS-CoV-2 infection, affecting individuals’ physical, mental, and social well-being [6].

Research indicates that Long COVID encompasses a wide array of symptoms, including fatigue, dyspnea, and neurological manifestations such as headache and attention deficit [7,8]. Moreover, severe complications like renal failure, pulmonary fibrosis, and myocarditis have been reported, posing significant challenges to patient management and recovery [5]. The prevalence of Long COVID varies among populations, with some studies reporting rates as high as 79.3% in certain regions [9].

Beyond physical symptoms, Long COVID also exerts profound psychological effects, including depression, anxiety, and post-traumatic stress disorder [10]. Factors such as age, comorbidities, and the severity of the initial COVID-19 infection contribute to the likelihood of developing Long COVID [11].

Against the backdrop of the fifth wave of the pandemic, characterized by the predominance of the Omicron variant since January 2022 [12], Thailand has intensified its vaccination efforts and adopted antiviral therapies. However, despite a decrease in severe COVID-19 cases during this wave, information regarding Long COVID in the context of the Omicron variant and post-vaccination remains scarce.

To address this gap, a prospective observational study was conducted at Maharaj Nakorn Chiang Mai Hospital—Faculty of Medicine, Chiang Mai University, aiming to elucidate the prevalence of Long COVID, associated factors, and holistic outcomes amidst widespread vaccination and antiviral availability in Thailand.

The study, approved by the Research Ethics Committee of Chiang Mai University (Study code: MED-2564-08702), commenced in February 2022, adhering to the Declaration of Helsinki guidelines [13]. A total of 390 participants with confirmed SARS-CoV-2 infection between January and April 2022 were enrolled, following informed consent. Data collection involved telephonic interviews conducted quarterly over a one-year period, starting three months post-diagnosis.

Demographic information, vaccination status, comorbidities, and treatment history were documented. Participants completed standardized questionnaires assessing physical manifestations, mental health, sleep quality, daytime function, and health-related quality of life post-COVID-19 recovery [14].

Physical manifestations were categorized into various symptom clusters, including general, respiratory, cardiovascular, neurological, gastrointestinal, dermatological, ear-nose-throat, musculoskeletal, immunological, and reproductive symptoms. Mental health assessments utilized validated scales such as the Patient Health Questionnaire (PHQ-9) for depression, Generalized Anxiety Disorder-7 (GAD-7) for anxiety, and screening questionnaires for post-traumatic stress disorder (PTSD) [15,16].

Sleep quality and daytime dysfunction were evaluated using the Pittsburgh Sleep Quality Index (Thai-PSQI), Epworth Sleepiness Scale (Thai-ESS), and Functional Outcomes of Sleep Questionnaire (FOSQ-10) [17]. Health-related quality of life was assessed using the 12-item short-form survey (SF-12) [18].

The study’s findings will provide valuable insights into the burden of Long COVID in the context of evolving viral variants and vaccination strategies, informing public health interventions and patient care strategies in Thailand and beyond.


The prospective observational study aimed to unravel the prevalence and associated factors of Long COVID amidst the fifth wave of the COVID-19 pandemic, characterized by the Omicron variant’s dominance. Notably, this wave saw a decline in severe cases, possibly attributed to enhanced vaccination coverage, booster doses, and the availability of antiviral drugs.

Of the 390 patients studied, 77.7% exhibited Long COVID symptoms, with fatigue and cough being the most prevalent. The persistence of cough correlated significantly with Long COVID development, indicative of ongoing viral activity and immune dysregulation. Mental health effects, including depression and anxiety, were observed in a subset of patients, alongside sleep disturbances, underscoring the multifaceted nature of Long COVID.

Interestingly, logistic regression analysis revealed a significant association between individuals under 60 years of age and Long COVID, contrary to prior research emphasizing age as a risk factor. Gender disparities were evident, with female patients reporting higher prevalence of certain symptoms like headaches and dizziness, suggesting potential hormonal or immunological influences.

Surprisingly, no significant link was found between comorbidities, initial infection severity, and Long COVID emergence, highlighting the complexity of symptomatology influenced by viral variants, vaccination status, and initial symptoms. The study’s observational nature warrants further prospective research to establish causal relationships and longitudinal studies to track symptom evolution over time.

Despite limitations, including reliance on patient-reported outcomes and lack of face-to-face evaluations, the study offers valuable insights into Long COVID’s manifestation amidst vaccination and antiviral availability. Methodological strengths, such as standardized telephone-based interviews, enhance data reliability, yet causative research is needed to refine diagnostic parameters.


The study underscores the significant burden of Long COVID despite vaccination and antiviral measures. Factors such as age, cough persistence, and gender disparities influence Long COVID prevalence and symptomatology. Mental health and sleep disturbances further compound Long COVID’s impact, emphasizing the need for holistic patient care.

The findings challenge previous assumptions regarding age and comorbidities’ role in Long COVID, highlighting the need for nuanced understanding influenced by viral variants and vaccination efforts. Longitudinal evaluations are imperative to elucidate symptom progression and intervention efficacy, shaping targeted approaches for Long COVID management.

reference link : https://www.mdpi.com/2077-0383/13/5/1208


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