No, a study has not shown that the covid jab causes cancer

Summary

More or Less – “No, a study has not shown that the covid jab causes cancer”

BBC Radio 4 | Host: Tim Harford | Date: January 17, 2026

---

Episode Overview

This episode of More or Less tackles a widely circulated claim that a recent study has shown a dramatic increase in cancer risk after COVID-19 vaccination. Listener Lyn asks host Tim Harford to scrutinize a viral statement made by content creator Kayla Betts, who referenced a peer-reviewed study from South Korea. With the help of Professor Justin Fendos, an expert in cancer biophysics and health informatics, Tim dissects the statistical methods and interpretations behind the alarming claim and explains why the conclusion is unfounded.

---

Key Discussion Points & Insights

1. The Origin of the Claim (01:18–02:20)

• Kayla Betts’ Statement:
  Betts claimed a peer-reviewed study of 8.4 million people (published September 2025 in Biomarker Research) found “a 27% overall increase in cancer risk in the vaccinated group in just the first year.”
• Tim Harford’s Response:
  The referenced publication was a “correspondence,” not a full research report. Biomarker Research does use peer review for regular papers, but “correspondence” may not undergo the same scrutiny.

2. Scrutinizing the Study’s Methods (03:14–05:29)

• Guest Expert:
  Professor Justin Fendos (Xian Jiaotong-Liverpool University, China) specializes in cancer, biophysics, and health informatics.
• Core Variables Considered:
  • Demographics: Age, gender, income.
  • Other Variables: Prior disease history (Charlson Comorbidity Index), COVID infection status, vaccination status, and cancer incidence (the outcome).
  • Key Omissions: Genetics, smoking status, previous cancer diagnoses, and health-seeking behaviors were not included.
• Health-Seeking Behavior Bias:
  Fendos points out that people proactive about their health tend to both get vaccinated and participate in cancer screenings, increasing diagnosis rates incidentally.

“People who really care about their health and engage in one or more health activities are also more likely to engage in other types of health activities.”
— Prof. Justin Fendos (04:53)

3. The Flawed Study Time Frame (05:29–06:08)

• Short Analysis Window:
  • Vaccinated: Cancer diagnoses checked within a year of vaccination.
  • Unvaccinated: Diagnoses checked within a year from Jan 1, 2022.
• Problem:
  Cancers typically take years, even decades, to develop.

“Any new diagnosis of cancer within a year of receiving the jab is very unlikely to have been caused by the vaccine, at least so far as we know.”
— Tim Harford (06:08)

4. Population Statistics & National Trends (06:34–06:44)

• Extremely High Vaccination Rates:
  South Korea’s vaccination uptake exceeded 96%.

• Real-World Data Mismatch:
  If the claim were valid, South Korea should be seeing a nationwide cancer spike, which isn’t happening.

5. Statistical Pitfalls: Hazard Ratios & Multiple Outcomes (07:11–08:34)

• Hazard Ratio Explained:
  Used to compare event rates (e.g., cancer) between groups.
• Multiple Outcomes:
  Study examined 29 cancer types. Checking many outcomes increases chances of finding significance just by chance (multiple comparisons problem).
• Critical Missing Correction:
  The study didn’t adjust (“statistical correction”) for checking so many outcomes. Such a correction substantially lowers the number of statistically significant findings.

“The more times you go fishing, the more likely you are just by random chance to catch something. And so you have to make an adjustment, a correction for this possibility. It looks like they did not do this kind of a correction.”
— Prof. Justin Fendos (08:38)

6. Findings Disappear With Proper Analysis (09:10–09:35)

• Correcting the Stats:
  Once the appropriate corrections are applied, the purported link between vaccination and increased cancer risk vanishes.

“If you do correct for the fact that so many outcomes are being studied, the relationship between the vaccines and cancer disappears.”
— Tim Harford (09:10)

• Conclusion:
  The analysis does not show the COVID vaccine increases cancer risk. The data was misinterpreted and possibly miscommunicated by those lacking statistical expertise.

---

Notable Quotes & Memorable Moments

• [02:32] “I do not believe that this paper decisively, definitively or even very convincingly shows that COVID vaccine uptake causes or is strongly related to cancer incidence.” — Prof. Justin Fendos
• [06:08] “Any new diagnosis of cancer within a year of receiving the jab is very unlikely to have been caused by the vaccine, at least so far as we know.” — Tim Harford
• [08:38] “The more times you go fishing, the more likely you are just by random chance to catch something. And so you have to make an adjustment, a correction for this possibility.” — Prof. Justin Fendos
• [09:35] “So, no, we do not have evidence that the vaccine causes cancer risks to rise.” — Tim Harford

---

Timestamps for Important Segments

• 01:18 — Host introduces the viral vaccine-cancer claim
• 01:51 — Kayla Betts presents the original claim
• 02:20–03:53 — Tim clarifies the study type, introduces guest expert
• 03:53–05:29 — Justin Fendos explains missing variables & health-seeking bias
• 05:37–06:08 — Prof. Fendos details flaws in the study’s time frame
• 06:34–06:44 — Vaccination rates in South Korea
• 07:11–08:34 — Explanation of hazard ratios and statistical significance
• 08:38–09:19 — Importance of statistical correction (multiple comparisons)
• 09:35 — Summary and conclusive dismissal of the claim

---

Closing

Tim Harford and guest Justin Fendos expertly debunk the claim that COVID-19 vaccines cause increased cancer risk, showing how important statistical rigor and domain knowledge are when interpreting medical studies. Careful statistical correction and context make clear there is no evidence supporting this alarming claim.

Listeners with further statistical questions are encouraged to write in to the show.

---

Transcript

[A]

This BBC podcast is supported by ads outside the uk. When you give to a nonprofit, how do you measure success? Many focus on low overhead, but what about real impact on people's lives? For 18 years, GiveWell has researched the highest impact giving opportunities. Over 150,000 donors have confidently used GiveWell, saving 300,000 lives and improving millions more. Make a tax deductible [e-mail] first time donors can have their donation matched to up to $100 while funds last select podcast and more or less at checkout. The best B2B marketing gets wasted on the wrong people so when you want to reach the right professionals, use LinkedIn ads. LinkedIn has grown to a network of over 1 billion professionals, including 130 million decision makers. And that's where it stands apart from other ad buys. You can target your buyers by job title, industry, company role, seniority skills, company revenue so you can stop wasting budget on the wrong AUD. It's why LinkedIn Ads generates the highest B2B return on ad spend of major ad networks. Spend $250 on your first campaign on LinkedIn Ads and get $250 credit for the next one. Just go to LinkedIn.com Broadcast that's LinkedIn.com Broadcast. Terms and conditions apply.

[B]

Hello and thanks for downloading the More or Less podcast. We're the programme that injects a shot of clarity into the sluggish arteries of statistical uncertainty. And I'm Tim Harford, loyal listener. Lyn wrote into more or lessbc.co.uk to ask us to look into a claim made by Kayla Betts. He's a right leaning content creator who focuses on mental health and well being. Lyn was sent his claim by her son and wanted us to throw some light on it as I think Kayla did too.

[C]

Nobody is talking about this study and it absolutely blows my mind. There was a study that was published on September 26, 2025 in Biomarker Research. It's a peer reviewed scientific journal with strong reputation that analyzed 8.4 million people.

[B]

Go on.

[C]

The study found a 27% overall increase in cancer risk in the vaccinated group in just the first year. How is this not the major headline story of every mainstream media outlet across the world right now? Like why aren't we talking about this?

[B]

Fair. Let's talk about it. The report was indeed published in a journal that uses peer review. However, the paper was published as a correspondence rather than a full blown report. Correspondence is reviewed at the editor's discretion. So although the journal that the paper was published in does use peer review for full reports. Correspondence articles might not, but it's to the data that we must really turn our attention. We spoke to Justin Fendos to help us sort through the stats.

[D]

I am a professor at Xian Jiaotong Liverpool University in the city of Suzhou in China.

[B]

Before coming to China, Justin spent 11 years as a professor at Dongje University in Busan, South Korea, specializing in cancer and biophysics. And these days his work focuses on big data health informatics, so using statistical.

[D]

Methods to try to understand predictors for different kinds of health outcomes in large data sets.

[B]

Ideal Justin has been poring over the report to see whether we can conclusively say that receiving the COVID vaccine causes cancer. And the results are no, I do.

[D]

Not believe that this paper decisively, definitively or even very convincingly shows that COVID vaccine uptake causes or is strongly related to cancer incidents.

[B]

Well, that's that. Although it's all very well us saying this, but you'd just be taking our word for it. So let's look more closely.

[D]

This kind of very large database contains a wealth of information. Virtually anything that would be in doctors files about patients would have been contained in this database. But for whatever reason, the researchers decided to essentially focus on seven different types of variables. Only the first three were demographic variables, so age, gender, income. The fourth was something called the Charles Comorbidity Index, which represents your previous disease history. The fifth type of variable that they looked at was the COVID infection history. The sixth type of variable was the vaccination history. And then the seventh type of variable, this was their output, the outcome that they wanted to study, which was the cancer incidence.

[B]

Importantly, they did not look at some vital variables that we know raise the risk of developing cancer, for example genetics or smoking. And we also don't know if they had a previous cancer diagnosis. They didn't account for people's health seeking behaviours either. And this is important.

[D]

I think it's pretty universally true that people who really care about their health and engage in one or more health activities are also more likely to engage in other types of health activities when presented the opportunity to do this.

[B]

So people who are more likely to get the vaccine are also more likely to go to GP checkups to sign up for cancer screening programs and so on. And South Korea is proactive in trying to diagnose cancers early.

[D]

South Korea does have pretty well organized screening programs, especially for the elderly or people who have been identified as high risk groups.

[B]

If you look for something you Are more likely to find it. There is another important question mark over this paper, and that's the time frame.

[D]

For the vaccinated people. They only look for new cancer diagnoses within a year of the first vaccination event. And then for the unvaccinated people, they look for new cancer diagnoses Within a year of an arbitrary date that they set, which was January 1, 2022. The issue here is that the time frame is very short. And if you understand molecularly and cellularly how cancers tend to develop, they tend to develop over many years, Sometimes even a decade or two.

[B]

Any new diagnosis of cancer within a year of receiving the jab Is very unlikely to have been caused by the vaccine, at least so far as we know. There are scare stories about turbo cancers, but so far there is no medical or scientific evidence that backs those stories up, no matter what people say at political party conferences and rallies. There is another problem with the findings. Almost all the population of south Korea were vaccinated.

[D]

The first wave of vaccinations, the uptake was extraordinarily high. I believe it was above 96%. The second wave was also very high, above 90%.

[B]

So if there really is a 27% increase in short term cancer risk for vaccinated people, South Korea should be experiencing a sharp rise in cases of cancer. It isn't. The final problem with this paper is a big one and also the name of a kraftwehrk inspired musical I'm writing the hazard ratio in statistics, the way we compare a rate of an event, in this case cancer that occurs in one group against another.

[D]

When the number is above one, it means that the probability for the vaccinated group is higher than the unvaccinated group. And then if the value of the hazard ratio is less than 1, that means the opposite, that the probability of cancer diagnosis for the vaccinated group is less than the unvaccinated group. Now, for this particular research, Instead of just looking at two or three specific types of cancers, they actually looked at a whopping 29 different types of cancers. And statistically, however, when you are looking at so many different outcomes, because each of these rates of cancer needs to be looked at as a unique potential outcome, you, have to do something called a statistical correction. And so you have to calculate statistical significance, which essentially is a number that describes how confident you can be that the shadows you are observing accurately represent the true object. And so the hazard ratio calculation is always accompanied by a measure of statistical significance. And so in this research, we were able to see that there were six specific types of cancers that exhibited this kind of statistical significance, that we could say that there is a potential real relationship between whether you were vaccinated or not and each of these different types of cancer diagnoses. So initially it looks good.

[B]

However, the authors missed out one very important step called a correction.

[D]

And the way the correction works is that you have to adjust the threshold for statistical significance. Essentially, the more outcomes you're looking at, the more you have to reduce your confidence in the statistical significance. Because it's like fishing. The more times you go fishing, the more likely you are just by random chance to catch something. And so you have to make an adjustment, a correction for this possibility. It looks like they did not do this kind of a correction.

[B]

If you do correct for the fact that so many outcomes are being studied, the relationship between the vaccines and cancer disappears.

[D]

It looks to me just by eye that probably most of their statistically significant results would actually disappear. So the six statistical significant cancer outcomes that they have here probably will be reduced to one or maybe even to zero.

[B]

So, no, we do not have evidence that the vaccine causes cancer risks to rise. It's easy to see why people look at the summary of these types of reports and take their findings at face value. But this type of paper is a statistical analysis. It doesn't tell you the underlying cause. And that's the problem with this sort of paper being reported by people who don't know how to read the data. Thanks to Justin Fendos and that's all we have time for this week. If you have any questions or comments, please do write in to more or lessbc.co.uk till next time. Goodbye.

[E]

If you're an H Vac technician and a call comes in, Grainger knows that you need a partner that helps you find the right product fast and hassle free. And you know that when the first problem of the day is a clanking blower motor, there's no need to break a sweat. With Grainger's Eclipse to use website and product details, you're confident you'll soon have everything humming right along. Call 1-800-GRAINGER Click grainger.com or just stop by Grainger for the ones who get it done. This is the story of the 1. As an H Vac technician, he and his digital multimeter are in high demand. So when a noisy office H Vac turns out to be a failing blower motor, he doesn't break a sweat. With Grainger's easy to use website and product information, he selects the product he needs to keep everything humming right along. Call 1-800-GRAINGER clickranger.com or just stop by Grainger for the ones who get it done.