SARS-CoV-2 infection can result in a variety of outcomes ranging from minor or no symptoms to hospitalization and death. Symptoms affecting those with post–COVID-19 conditions include fatigue, shortness of breath, joint pain, anxiety, and depression. Post–COVID-19 conditions may vary with viral variants. Understanding these diverse outcomes has improved even as new variants emerge. However, researchers point out the importance of evaluating post–COVID-19 condition risk in a range of populations, including younger, healthier, and lower-risk individuals.

While data show that SARS-CoV-2 vaccination is highly protective against acute symptoms, hospitalization, and death, the relationship between vaccination and post–COVID-19 conditions remains unclear. Studies suggest that vaccination after infection may mitigate long COVID risks. If vaccination either before or after infection is proven to decrease post–COVID-19 condition impacts, stronger arguments for vaccination would emerge. Therefore, further evidence is much needed to clarify vaccination's role as a post–COVID-19 condition intervention.

The Epidemiology, Immunology, and Clinical Characteristics of Emerging Infectious Diseases with Pandemic Potential (EPICC) study -- a longitudinal observational cohort study of 1,832 U.S. Military Health System beneficiaries aged 18 or older who tested positive for SARS-CoV-2 from February 28, 2020, through December 31, 2021, with a one-year follow-up -- sought to describe clinical SARS-CoV-2 infection outcomes.

Researchers described long-term post-COVID-19 experiences and factors associated with post–COVID-19 condition risk in the study cohort, quantified the association of vaccination both before and after infection with persistent COVID-19 symptoms, and compared the frequency of organ-specific healthcare events before and after SARS-CoV-2 infection.

The study found that the risk of reporting symptoms for 28 or more days after COVID-19 onset was significantly higher in participants who were unvaccinated at the time of infection, as well as in those who reported moderate or severe symptoms. At six months post-onset, these participants had a significantly higher risk of pulmonary, diabetes, neurological, and mental health events compared with their preinfection baseline. The findings suggest that vaccination is associated with a lower risk of long-term COVID-19 symptoms.

More severe acute illness, a higher Charlson Comorbidity Index score (a determinant of mortality), and being unvaccinated were all associated with a higher risk of reported COVID-19 symptoms lasting at least 28 days. These participants were more likely to seek medical care for diabetes, pulmonary, neurological, and mental health-related illness for at least six months after onset compared with their pre-COVID-19 baseline patterns. The researchers note that understanding the factors associated with long-term post-COVID conditions may be key to their prevention, and hope their findings will better inform the risk-benefit ratio of COVID-19 vaccination policy.