Coronavirus disease (COVID-19) is a viral disease caused by SARS-CoV-2 that was declared an outbreak by the World Health Organization (WHO) in March 2020 [1]. Following an acute infection, multi-organ and long-lasting symptoms have been reported [2]. In October 2021 the WHO released a clinical case definition of post COVID-19 condition. The clinical case definition of post COVID-19 condition, or post-acute sequelae of COVID-19 (PASC), includes having symptoms developed within three months after infection with SARS-CoV-2. Common post-COVID-19 symptoms typically include fatigue, shortness of breath, and cognitive dysfunction. Considering the significant burden of disease [3], it is critical to identify risk factors and prevalence of post-acute sequelae to analyze the cost and consequences beyond an acute infection.

There are a wide range of estimates on the prevalence of PASC, which could be explained by the variance in definitions and follow-up time. One meta-analysis of 63 studies from 22 countries in different world regions examined the prevalence of PASC at different follow-up times. The prevalence of at least one symptom was estimated to be 63.2% at 30 days after COVID-19 symptom onset. The prevalence of at least one symptom was estimated to be 71.9% at 60 days after symptom onset, and a prevalence of 45.9% at 90 days after symptom onset. The highest prevalence for symptoms was fatigue and dyspnea, and this ranged from 35 to 60% depending on the follow-up time [4]. Conversely, a symptom-tracking study in the United Kingdom estimated the prevalence of PASC among 4,182 individuals and found that 13% of individuals self-reported symptoms after one month of COVID-19 symptom onset and 4.5% at two months [5]. Further research is needed to accurately understand the prevalence of PASC.

Possible risk factors for PASC include specific sociodemographic characteristics, COVID-19 vaccination status, SARS-CoV-2 variant, presence of comorbidities, and severity of initial infection [6], [7], [8], [9], [10], [11]. However, the evidence for these risk factors is mixed. In a cross-sectional study of 274 individuals with COVID-19, individuals of older age and severe illness were found to be more likely to have persistent symptoms following acute infection [9]. Conversely, in a prospective cohort study of 1,038 US adults, researchers suggested that hospitalization for COVID-19, having diabetes, having a high BMI were independently associated with PASC development. This study found no differences in age, race/ethnicity, or Social Vulnerability Index for developing PASC [11]. There is limited evidence examining if the risk of PASC is impacted by the variants of SARS-CoV-2. One case-control observational study of 56,003 omicron strain cases and 41,361 delta strain cases, found a reduction in the odds of PASC with the omicron variant compared to the delta variant [12]. There is a critical need for future research to identify risk factors so targeted intervention strategies may be implemented.

There have been few studies examining PASC in the US Veteran population [13], [14], [15], [16], [17]. The US Department of Veterans Affairs (VA) electronic health databases offers robust data relating to COVID-19 and individual level patient sociodemographic. In a cohort study of 33,940 veterans with breakthrough infections, results demonstrated that patients with a breakthrough infection had a higher risk of developing PASC compared to patients with no history of COVID-19 [17]. However, with updated COVID-19 vaccination guidelines [18], future research should examine how risk of PASC development changes with number of vaccines received. Moreover, in another retrospective cohort study of 198,601 US Veterans, results suggested older age, Black or American Indian/Alaska Native race, Hispanic ethnicity, urban residence, high Charlson Comorbidity Index score, and requiring hospitalization as potential risk factors [19]. However, one limitation to this study is that the outcome of PASC was defined by documentation of the long COVID-19 ICD-10 code (U09.9). The true prevalence and risk factors may be underrepresented by not incorporating other documented symptoms.

Health officials are predicting a major health crisis as a direct result of PASC; thus, further investigation is needed to determine at-risk populations [20]. While there is considerable evidence for the risk factors, mechanisms, and treatment for acute SARS-CoV-2 infection, there is limited literature about PASC. VA-specific research thus far has suggested systemic health conditions following an acute infection and shows an increased risk in individuals with severe acute infection [14], [16]. There is a considerable need for research concerning the risk factors for PASC. Furthermore, the current VA-specific research utilizes the ICD-10 code alone in defining PASC. This may lead to an under-ascertainment of cases considering it was not released until October 2021. In addition, it may not be inclusive of all possible post-acute sequelae, such as extrapulmonary symptoms. Therefore, this study aims to better understand PASC in the Veteran population. Specifically, this analysis has three main objectives: 1) to determine the prevalence of PASC in the Veteran population; and 2) to identify key sociodemographic, SDOH, and clinical risk factors for PASC development.