“Does Getting a COVID-19 Vaccine Cause Cancer?” Study of 36.02 Million People Yields Results

[Financial News]  A new finding has emerged that differs from previous studies suggesting COVID-19 vaccination increases the risk of cancer. An analysis of health insurance data for about 36.02 million people in South Korea found no statistically significant changes in incidence trends across 13 major cancer categories during the approximately 50 months after vaccination.
At a media briefing held online on the 29th by the Korea Science and Technology Media Center (SMCK), Professor Jeong Jae-hoon of the Department of Preventive Medicine at Korea University College of Medicine said, “We analyzed cancer incidence trends nationwide for 50 months after vaccination,” adding, “No particular changes were observed after vaccination; the trend remained the same as before.”
The research team combined National Health Insurance Service (NHIS) health insurance data with COVID-19 vaccination records to examine cancer incidence trends among 36,024,394 people born between 1955 and 2004. The study was recently published in the international journal Biomarker Research.
The analysis used August 2021 as its reference point, when the share of people in South Korea who had received a first dose of a COVID-19 vaccine reached 50%. The researchers compared cancer incidence trends over the roughly 10 years before vaccination, from February 2011 to July 2021, with changes during the 50 months afterward, through September 2025.
None of the 13 cancer categories included in the analysis showed a statistically significant change in incidence trends. The same was true when stomach, colorectal, lung and prostate cancers were analyzed separately.
Professor Jeong explained, “For some cancers, incidence may appear to have increased after cancer screening itself fell sharply during the COVID-19 pandemic and social distancing measures were lifted.” However, he added, “Even after adjusting for related factors, no particular upward trend was identified for any cancer.”
This study found a different result from research published last year on vaccination and cancer risk. In September 2025, a research team that included Professor Chun Eun-mi of the Department of Pulmonology at Ewha Womans University Mokdong Hospital analyzed health insurance data for Seoul residents and reported that people vaccinated against COVID-19 had a higher risk of major cancers within one year of vaccination than unvaccinated people.
At the time, some argued that it was difficult to establish a causal relationship between vaccination and cancer. Concerns were also raised in the medical community that the study could increase anxiety about vaccines and reluctance to get vaccinated.
Professor Jeong said the observation period in the earlier study was not long enough to assess the relationship between cancer and vaccination. “Even cancers that develop the fastest have a latency period of at least one year, and most have a latency period of five to 10 years,” he said. “It is difficult to establish an association between vaccination and cancer based on about one year of observation.”
There was also little difference between vaccine types. In a separate paper published in the journal of the Korean Academy of Medical Sciences, Professor Jeong’s research team reported no major difference in changes in cancer incidence rates between viral vector COVID-19 vaccines and messenger RNA (mRNA) vaccines.
Professor Jeong also described as an “epidemiological error” claims raised in some quarters overseas, including the United States, that COVID-19 vaccines are linked to an increase in cancer. He said it was necessary to distinguish the effects of vaccination from the rise in the number of cancer cases that accompanies population aging.
“Populations are aging around the world, and cancer incidence rises with age,” Professor Jeong said. “Looking only at the raw number of cases may make it seem as though cancer incidence is increasing, but the actual trend has not changed.”
Professor Jeong said, however, that this study alone could not fully assess the causal relationship between vaccination and cancer. As an observational study, it has limitations in establishing causality to the same standard as a clinical trial.
“In medicine, assessing complete causality means conducting a Phase 3 clinical trial,” he said. “This does not mean the study itself has serious flaws, but please bear in mind that, because it is an observational study, it is difficult to establish causality to the standard of a Phase 3 clinical trial.”


[email protected] Han Seung-gon Reporter