Half of hospitalized COVID-19 patients developed long COVID

Half of hospitalized COVID-19 patients developed long COVID

A two-year study from Thailand shows how often COVID follows hospitalization, how long symptoms can last and why vaccination and disease severity have a crucial impact on patients' long-term quality of life.

Study: Prevalence and impact of long-COVID on health-related quality of life in previously hospitalized COVID-19 patients: a 2-year follow-up study. Photo credit: MW Shutter/Shutterstock.com

A new study published inScientific reportsfinds a high prevalence of long-COVID among patients in Thailand hospitalized due to symptomatic coronavirus disease 2019 (COVID-19) in 2021.

Long-term COVID symptoms persist for years after infection

The COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has placed a significant burden on the global health system since its outbreak in 2019. The threat remains in 2025 as a significant proportion of previously infected individuals still experience persistent symptoms of COVID-19, a condition medically referred to as long COVID.

The World Health Organization (WHO) defines long COVID as the persistence or development of new symptoms three months after the first SARS-CoV-2 infection, with these symptoms lasting at least two months without any other explanation.

The global prevalence of long-COVID is estimated to be approximately 36% to 43%, with a higher prevalence observed in hospitalized COVID-19 patients. Studies examining long-term COVID risk factors have identified female gender and acute COVID-19 severity as important predictors, and COVID-19 vaccination as an important protective factor.

Studies analyzing the prevalence, predictors and outcomes of long-COVID have been predominantly conducted in high-income countries. In low- and middle-income countries, particularly in Southeast Asia, evidence is limited. The reported prevalence of long COVID in Southeast Asia ranges from 3.4% to 47%. However, most studies lack long-term follow-up.

Given this gap in the literature, researchers at Mahidol University in Thailand conducted a study to determine the prevalence and predictors of long-term COVID-19 illness among hospitalized patients.

Tracking Long COVID Symptoms After Hospital Discharge

The study population included a total of 295 adult patients who were admitted to hospital wards and intensive care units between August and November 2021 for symptomatic COVID-19 disease.

Patients were followed up three months, one year, and two years after infection through telephone interviews. During the interviews, patients were asked about long-term COVID symptoms and whether these symptoms affected their daily life.

Patient demographic characteristics such as gender, age at infection, body mass index, comorbidities and vaccination status, as well as clinical information during hospitalization, including disease severity, were analyzed to identify predictors of long COVID.

Symptoms persisted for up to two years after infection

The study estimates found that the prevalence of long COVID in hospitalized patients three months after acute SARS-CoV-2 infection was 49.8%. The most common symptoms were shortness of breath, hair loss, fatigue, muscle pain and chest pain.

Symptoms of long COVID persisted for one year in 64% of patients reporting long COVID at three months and for two years in 22% of patients who remained symptomatic at one year, highlighting the conditional nature of long-term persistence. Notably, the study found an increasing prevalence of neurocognitive symptoms one year after infection. The five most commonly reported persistent symptoms were shortness of breath, memory impairment, fatigue, cough and peripheral numbness.

Analysis of predictors and protective factors revealed that patients with severe to critical acute COVID-19 disease have a significantly higher risk of developing long COVID disease. However, patients who received a full two-dose vaccination before the outbreak of COVID-19 have a significantly lower risk of developing long COVID.

Serious illness increases the risk, while vaccination protects

The study reports a high prevalence of long-COVID among previously hospitalized patients in Thailand, with symptoms persisting over a period of two years in a significant proportion of affected individuals. These results are concerning because persistent symptoms of long-COVID have been found to impact the daily lives of affected individuals.

Among reported symptoms, joint pain showed a significant association with perceived impact on daily life. Other reported symptoms that often impact participants' daily lives include fatigue, difficulty sleeping, decreased appetite, and muscle pain.

According to the results, a severe to critical case of acute COVID-19 disease is a significant risk factor for long-term COVID disease, while full vaccination protects against the disease. These two factors are also important predictors of the perceived impact of long-COVID on daily life.

By analyzing the demographic characteristics of participants who reported impairment in daily life, the study finds that men are less likely than women to develop long COVID affecting daily life. The differences in inflammatory profiles and airway morphology between genders may contribute to a higher risk of long-term COVID in women.

Overall, the study results provide an overview of the long-term impact of COVID-19 on hospitalized Thai individuals and fills a gap in the literature for low- and middle-income countries.

The study had a small sample size and a high loss-to-follow-up rate, which may limit the accuracy of prevalence estimates. The exclusive inclusion of hospitalized Thai patients may limit the generalizability of the results to non-hospitalized patients and other nationals.

The study was conducted during the Delta variant outbreak and the prevalence and impact of Long-COVID may differ from those of other SARS-CoV-2 variants. In addition, the study may underestimate the protective effect of vaccination against long COVID symptoms because there is no data on the time between vaccination and the onset of infection.

The study lacks data on repeat COVID-19 infections and therefore could not demonstrate the impact of reinfection on the epidemiology of long-term COVID. The lack of a comparison group of people without COVID-19 limits the conclusion that the reported symptoms are solely sequelae of COVID-19.

Larger, multicenter studies with appropriate comparison groups are needed to more accurately estimate prevalence and better understand the health outcomes associated with long-term COVID.

Download your PDF copy now!

Sources: