Kinetics of the PASC Index in Long COVID

by Kyungsup Kwon, Choi Young Jang, Woori Kim, JuYeon Son, Euijin Chang, Sung-Han Kim

Background

The post‑acute sequelae of SARS‑CoV‑2 infection (PASC, “Long COVID”) remain difficult to evaluate because standardized diagnostic tools are limited. We applied the recently proposed PASC index (score ≥ 12) to describe the 12‑month trajectory of Long COVID symptoms.

Methods

In this prospective cohort, adults with laboratory‑confirmed COVID‑19 were consecutively enrolled from November 2022 to February 2025. Long COVID was defined by a PASC index of ≥12 across 12 symptom domains persisting for at least 30 days post-infection. Symptom questionnaires were completed at 1, 3, 6 and 12 months after infection.

Results

Among 183 participants, 48 (26.2%) met Long COVID criteria. Symptom assessments indicated that the proportion of participants meeting the Long COVID threshold declined from 27% at 1 month to 18% at 12 months, although this change was not statistically significant (p = 0.16). Participants classified as having Long COVID had consistently higher PASC index values across follow-up, while pairwise within-person comparisons showed no significant temporal changes in either the Long COVID or non-Long COVID group. These findings suggest that the overall symptom burden remained relatively stable over time, despite fluctuations in threshold status.

Conclusion

During 12 months of follow-up, approximately one quarter of participants met the PASC index threshold at least once. Among participants with repeated assessments, PASC index scores showed limited within-person change, although differential non-response limits the interpretation of temporal prevalence estimates.