A Biostatistical Reappraisal Unveiling the Mechanism Behind Apparent Cancer Risk Signals in a COVID-19 Vaccinated Cohort

Abstract (Unstructured): A large-scale South Korean cohort study reported an apparent signal suggesting a higher cancer risk among COVID-19–vaccinated individuals [1]. However, a preliminary analysis had already indicated that the cohort’s overall cancer incidence was historically 22.6% lower than the national average, a deficit confirmed at 26.3% using the most recently available {2022} national rates. Our primary objective was to quantitatively verify wether an asymmetry in the underrepresentation of high-risk elderly individuals (>=65) was the mechanism that mathematically generateed this apparent risk signal. To investigate this, we performed a rigorous biostatistical comparison, analyzing age-stratified demographic composition and corresponding cancer case counts (Table S4 in [1]) against o/icial Korean national standards (2022) to reconstruct and evaluate Crude Incidence Rates (CRs) The analysis confirmed that the total study cohort markedly underrepresented participants aged >= 65 by 31.1% overall. Importantly, the non-vaccinated subgroup aged >= 65 showed an even more severe cancer undercount of 45.5% relative to the coherent national rate. This profound, asymmetric underrepresentation within the high-risk non- vaccinated cohort segment explains the 26.3% suppression of the overall cohort incidence and, consequently, mathematically produces the spurious excess risk observed among vaccinated individuals. We conclude that the reported increase in cancer risk is most likely a statistical artifact stemming from severe, asymmetric selection bias in cohort enrollment, and that methodologically sound and demographically balanced cohorts would likely demonstrate no statistically significant di/erence in cancer incidence between vaccinated and non-vaccinated groups.