Intro:

A new large-scale retrospective cohort study from South Korea analyzes data from 8,407,849 individuals (2021–2023) to examine 1-year cancer incidence following COVID-19 vaccination. The authors report elevated hazard ratios for several cancers (thyroid, gastric, colorectal, lung, breast, prostate) associated with different vaccine types (cDNA, mRNA, heterologous) after adjusting for demographics and comorbidities. 

Given the sensitive nature of this topic and the potential for misinterpretation, it’s critical to frame the findings with care: these are associations, not proven causal effects. Further research, longer follow-up, mechanistic insight, and peer review are all needed.

The oncogenic potential of SARS-CoV-2 has been hypothetically proposed, but real-world data on COVID-19 infection and vaccination are insufficient. Therefore, this large-scale population-based retrospective study in Seoul, South Korea, aimed to estimate the cumulative incidences and subsequent risks of overall cancers 1 year after COVID-19 vaccination. Data from 8,407,849 individuals between 2021 and 2023 were obtained from the Korean National Health Insurance database.

The participants were categorized into two groups based on their COVID-19 vaccination status. The risks for overall cancer were assessed using multivariable Cox proportional hazards models, and data were expressed as hazard ratios (HRs) and 95% confidence intervals (CIs). The HRs of thyroid (HR, 1.351; 95% CI, 1.206–1.514), gastric (HR, 1.335; 95% CI, 1.130–1.576), colorectal (HR, 1.283; 95% CI, 1.122–1.468), lung (HR, 1.533; 95% CI, 1.254–1.874), breast (HR, 1.197; 95% CI, 1.069–1.340), and prostate (HR, 1.687; 95% CI, 1.348–2.111) cancers significantly increased at 1 year post-vaccination.

In terms of vaccine type, cDNA vaccines were associated with the increased risks of thyroid, gastric, colorectal, lung, and prostate cancers; mRNA vaccines were linked to the increased risks of thyroid, colorectal, lung, and breast cancers; and heterologous vaccination was related to the increased risks of thyroid and breast cancers. Given the observed associations between COVID-19 vaccination and cancer incidence by age, sex, and vaccine type, further research is needed to determine whether specific vaccination strategies may be optimal for populations in need of COVID-19 vaccination.

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Important Notice:

The following article summarizes findings from an independent, peer-reviewed epidemiological study conducted in South Korea and does not represent medical advice, policy guidance, or the views of Klean Industries Inc.

The study identifies statistical associations between COVID-19 vaccination and cancer incidence within a 1-year observation period. These associations do not imply causation.

Epidemiological data are influenced by multiple variables — including health status, environmental exposure, lifestyle, genetics, and screening rates — that can affect outcomes. The study authors themselves recommend further longitudinal and mechanistic research before drawing any clinical or policy conclusions.

Readers should consult qualified health professionals and official public health authorities for medical guidance.

Klean Industries supports open scientific dialogue, transparent data reporting, and responsible communication of research findings within the broader context of sustainability, innovation, and public well-being.