SV40, Polio Vaccines, and the Cancer Claim That Won’t Die

SV40, cancer, and a fundamental misunderstanding of virology

SV40, Polio Vaccines, and the Difference Between Laboratory Biology and Human Disease

I was a child who had one of the first polio vaccines (Salk), and then the second (oral) from Sabin. We lined up in school to get this vaccine, and while I never did like getting a shot, we were enthused to get a vaccine to prevent an illness that led to death.

Then came this video of Robert F. Kennedy Jr., claiming the polio vaccine contained SV40, describing it as "one of the most carcinogenic materials known to man," and suggesting it caused a cancer epidemic in his generation.

As someone trained in virology, including the use of tissue culture systems, this is a claim that merits careful, factual explanation( yes, when you are as old as I am you have done a few things in life). SV40 is real. The history is real. The conclusion RFK Jr. draws is not.

Here is the clip and the X (formerly tweet)

healthbot@thehealthb0t

RFK Jr: "The polio vaccine contained a virus called SV40." "It's one of the most carcinogenic materials that is known to man." "But it was in that vaccine. 98 million people... in my generation got it." "And now you've had this explosion of soft tissue cancers in our

12:26 AM · Dec 23, 2025 · 159K Views

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156 Replies · 2.36K Reposts · 6.09K Likes

What Is True (and What Is Not)

Yes, some early polio vaccines produced between 1955 and 1961 were contaminated with SV40, a simian polyomavirus present in monkey kidney cells used for viral culture at the time.

That contamination was:

• identified

• investigated

• eliminated by changes in manufacturing

SV40 has not been present in polio vaccines for more than 60 years. Or since I was a child.

What matters is not whether SV40 existed, but whether it caused the sweeping human cancer epidemic, as RFK Jr. claims.

What the Evidence Shows

SV40 can transform cells in vitro (in a petri dish) and cause tumors in some animal models (mice but I don’t care of a mouse gets cancer). That is precisely why it became useful as a laboratory tool for studying oncogenesis (or how cancer forms).

However, decades of epidemiologic follow-up of millions of people exposed to SV40-contaminated vaccines (like me) show:

• No consistent increase in cancer incidence

• No distinctive tumor pattern

• No population-level cancer signal attributable to SV40 exposure

If SV40 contamination had caused widespread cancer in humans, the signal would be unmistakable by now. It is not.

Cancer trends over the last half-century are explained by:

• aging populations

• smoking

• obesity

• environmental exposures

• improved screening and detection

Not by early-era polio vaccines.

Some viruses do cause cancer

Part of my research in grad school was the connection between viruses and cancer. When I was a graduate student, we saw that viruses caused cancer in animals, but had yet to find any connection to humans. However, we now have several positive links:

Only a small number of viruses are known to cause cancer in humans, and they do so through specific, well-documented mechanisms. Importantly, each has a clear epidemiologic signal — something SV40 does not.

Human Papillomavirus (HPV)

• Causes cervical cancer, most anal cancers, and many oropharyngeal cancers

• Mechanism: viral oncoproteins (E6, E7) disable tumor suppressors (p53, Rb)

• Strong, consistent population data

• Preventable by vaccination - which is why my son is vaccinated against this one.

Hepatitis B Virus (HBV)

• Causes hepatocellular carcinoma

• Mechanism: chronic inflammation, cirrhosis, viral DNA integration

• Clear dose–response relationship

• Preventable by vaccination - like we do when children are born.

• This is the great work from Alaska I talked about in a previous video and writing

Hepatitis C Virus (HCV)

• Causes liver cancer

• Mechanism: chronic inflammation and fibrosis

• Cancer risk falls dramatically after viral eradication. We don’t have a vaccine yet, we do have some potent anti-viral agents for some Hepatitis C infections.

Epstein–Barr Virus (EBV)

• Associated with Burkitt lymphoma, nasopharyngeal carcinoma, some Hodgkin lymphomas

• Mechanism: latent infection and immune dysregulation

• Cancer occurs in specific geographic and immune contexts. This was a highly speculative years ago, and a cause of great debates. The debate is over.

Human T-Lymphotropic Virus Type 1 (HTLV-1)

• Causes adult T-cell leukemia/lymphoma

• Mechanism: viral transactivation of cell growth pathways

• Rare but definitive

Kaposi Sarcoma–Associated Herpesvirus (HHV-8)

• Causes Kaposi sarcoma

• Occurs primarily in immunocompromised hosts, typically in AIDS patients

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What These Viruses Have in Common

• Persistent infection (SV 40 doesn’t do this to humans)

• Clear mechanisms of oncogenesis

• Reproducible epidemiologic evidence (not seen in people)

• Strong population-level cancer signals (only found in the mind of RFK Jr and his followers)

SV40 has none of these in humans.

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Key Takeaway

Many viruses can transform cells in a lab.
Very few cause cancer in people.

The difference is not semantics — it’s epidemiology.

Why This Claim Persists

SV40 is frightening-sounding, biologically interesting, and real. That makes it attractive to those who conflate laboratory findings with human outcomes.

But biology does not work by narrative. It works by evidence.

A virus that transforms cells in a dish does not automatically cause cancer in humans. Many viruses can disrupt cell cycles under artificial conditions. Very few cause cancer in real life.

This distinction is foundational in virology—and is exactly where RFK Jr.’s argument fails.

Good References

For readers who want to verify the facts directly:

Key References Supporting the Facts

• Contaminated polio vaccines and SV40:
  — Strickler et al., JAMA, 1998; PMID 9816320 — no elevated cancer rates in exposed cohorts. JAMA Network
  — Stratton et al., NCI review — large epidemiologic evidence does not support a causal link. PubMed
  — Engels et al., JNCI, 2003; PMID 12837733 — cancer incidence not higher in SV40-exposed groups. OUP Academic
  — CDC historical review — SV40 contamination was removed from vaccines after 1963. CDC

• COVID-19 vaccine effectiveness in New Zealand:
  — Datta et al., Vaccine, 2024; PMID 38307744 — modeling suggests vaccines prevented thousands of deaths and hospitalizations. PubMed
  — Mbinta et al., NZMJ, 2024; PMID 39236327 — retrospective cohort showing strong vaccine protection. PubMed

• General effectiveness signals:
  — CDC Emerging Infectious Diseases cohort showing lower severe outcomes in vaccinated vs unvaccinated. CDC
  — Global modeling (Ioannidis, 2025) showing millions of deaths averted. JAMA Network

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Final Thought

SV40 contamination was a manufacturing problem discovered and corrected in the early days of vaccine production. It did not cause a cancer epidemic.

Confusing laboratory biology with human epidemiology is not skepticism.
It is misunderstanding how science works.

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🔒 Paid Section: A Biological Primer — SV40 vs Poliovirus (For Non-Scientists)

(This section is for readers who want to understand the biology, not just the headlines and about how a virus can cause cancer.)