"Do COVID-19 Vaccines Cause Cancer?" ... Analysis of 36 Million Reveals 'Surprising' Results

Researchers: "No evidence of increased risk for any of the 13 cancers after vaccination"

A study analyzing health insurance data for approximately 36 million people in South Korea found no significant association between COVID-19 vaccination and trends in cancer incidence.

A COVID-19 vaccination site. The photo is not directly related to the article.

On October 29, Professor Jeong Jae-hoon of the Department of Preventive Medicine at Korea University College of Medicine presented two papers containing these findings at a briefing hosted by the Korea Science and Technology Media Center (SMCK). He said, "Based on the evidence currently available, we cannot conclude that vaccines increase cancer risk."

A paper recently published by Professor Jeong in the international journal Biomarker Research analyzed cancer incidence trends among 36,024,394 people born between 1955 and 2004. The study linked data from the National Health Insurance Service with COVID-19 vaccination records.

Using August 2021, when the primary vaccination rate in South Korea exceeded 50%, as the reference point, researchers analyzed whether cancer incidence trends over the following 50 months differed from those over the preceding decade or so. They found no significant changes in incidence levels or upward trends across any of the 13 cancer categories. Professor Jeong's research team also confirmed in a paper published in the Journal of the Korean Medical Association that no major difference could be observed in changes in cancer incidence rates between COVID-19 vaccines using viral vectors and messenger RNA (mRNA) vaccines.

Uhm Joong-sik, a professor of infectious diseases at Gachon University Gil Medical Center, said, "This study will be useful in removing barriers for people who feel anxious about getting vaccinated in real-world settings." He added that the findings were timely because they make it possible to explain that there is no need to worry that vaccination increases cancer incidence. Professor Uhm also said, "It is very difficult to find systematic reports of an increase in cancer following COVID-19 vaccination," adding, "Some have even suggested that mRNA vaccines may have a positive effect on the immune system and could be associated with a downward trend in some solid tumors or blood cancers."

Professor Jeong also said, "In science, reports of 'negative results'—that an effect did not occur—are rarely produced because they are considered self-evident." He added, "I believe the journal published our findings to help address people's concerns."

However, Professor Jeong emphasized that the current evidence, including this study, does not allow researchers to conclude that vaccination increases cancer risk, and that long-term monitoring is needed.

Meanwhile, a paper published in the international journal Biomarker Research in September 2025 reported an increased risk of stomach, colorectal, lung, and breast cancers, among others, within one year of vaccination. The study compared 2.38 million people who had received a COVID-19 vaccine with 590,000 unvaccinated people. Experts have pointed out that the paper has serious flaws. They explained that cancer takes at least several years to develop after exposure to risk factors, so an increase in cancer just one year after vaccination is merely a "statistical illusion."

This content was produced with the assistance of AI translation services.