Abstract
BACKGROUND: Long COVID can persist for years, but little is known about its prevalence in relation to the number of infections. This study examines the prevalence of long COVID in association with the number of infections and vaccination status. METHODS: We analyzed anonymized data on long COVID cases, thrombotic events and polypharmacy from March 2020, provided by the Data Analysis Control Department for the population assigned to the CST (192,651 at March 2025). Additionally, we analyzed responses to a long COVID symptom-specific survey distributed in March 2024 to individuals aged 18 to 75 years from the CST population diagnosed with COVID-19 as of December 2023 (n = 43,398; 3227 respondents). Symptomatic patients suspected of having long COVID underwent blood tests to exclude alternative diagnoses. RESULTS: The overall detected prevalence of long COVID was 2.4‱, with higher frequency among women aged 30-59 years (p < 0.001). The survey, combined with specific blood tests, improved detection rates by 26.3%. Long COVID prevalence was 3-10 times higher in individuals with three or more infections than in those with only one recorded infection (based on survey/CST data, respectively). The absolute number of thrombotic events among individuals aged >60 doubled from 2020 to 2024, occurring in both vaccinated and unvaccinated individuals, as well as in those with or without prior documented COVID-19 infection, including in patients without chronic treatments. CONCLUSIONS: We found a link between SARS-CoV-2 reinfection and long COVID, and a post-pandemic rise in thrombotic events across all populations, regardless of vaccination or prior infection. Findings support continued COVID-19 diagnosis in suspected cases and mask use by healthcare workers treating respiratory patients.