10/02/2025
Design & data: Population-based retrospective cohort using the Korean National Health Insurance database (2021–2023).
Population: 8,407,849 adults.
Exposure: COVID-19 vaccination (analyzed overall and by platform: mRNA, cDNA, and heterologous schedules).
Matching: Large-scale propensity score matching (1:4 vaccinated:unvaccinated for the main analysis; 1:2 within vaccinated for booster vs non-booster).
Modeling: Multivariable Cox proportional hazards models (adjusted for age, s*x, comorbidity index, income level, and prior COVID-19 infection), estimating hazard ratios (HRs) with 95% confidence intervals (CIs); analyses stratified by s*x and age.
Outcome window: 1-year incidence of overall and site-specific cancers post-vaccination.
cDNA vaccines (AstraZeneca type): linked to higher risks of thyroid, gastric, colorectal, lung, and prostate cancers.
Overall cancer HR 1.47 (95% CI 1.39–1.56) → 47% higher risk
mRNA vaccines (Pfizer/Moderna): linked to higher risks of thyroid, colorectal, lung, and breast cancers.
Overall cancer HR 1.20 (95% CI 1.14–1.26) → 20% higher risk
Heterologous (mixed schedules): linked to higher risks of thyroid and breast cancers.
Overall cancer HR 1.34 (95% CI 1.21–1.48) → 34% higher risk
