Correlation Is Not Causation, Except When It Is: Lessons from Thalidomide, Smoking, Asbestos, and mRNA Vaccine Concerns

Disclaimer: This post is for informational purposes only and not medical advice. Always consult a qualified healthcare professional for medical concerns.

The Mantra: Correlation Does Not Imply Causation

We’ve all heard the phrase “correlation is not causation.” (Oller & Santiago 2022, pg 315 ) It serves as a cornerstone of critical thinking in science, reminding us that just because two things happen together, like ice cream sales and drowning rates spiking in summer, does not mean one causes the other (spoiler: warm weather drives both). This principle protects us from drawing flawed conclusions based solely on associations. However, sometimes correlation does point to causation when backed by robust evidence. In the following sections, I will examine three historical cases, thalidomide, smoking, and asbestos, where correlations ultimately led to confirmed causation. I will then apply the same level of scrutiny to recent concerns regarding unusual fibrous amyloidogenic clots (see image 1 and my last Substack post) and myocarditis following mRNA COVID-19 vaccines.

Image 1: Unusual fibrous amyloidogenic clots. For laboratory analysis please read Kevin McCairn Ph.D. work: https://substack.com/@kevinwmccairnphd282302

Thalidomide: A Tragic Lesson in Causation
In the late 1950s, thalidomide was marketed as a safe sedative and frequently prescribed to pregnant women for nausea. By the early 1960s, a chilling pattern emerged: women who took the drug during pregnancy were far more likely to give birth to babies with severe limb deformities, like phocomelia. Phocomelia (foh-koh-MEE-lee-uh) is a rare birth condition where a person’s arms or legs are very short or missing, often causing hands or feet to be attached close to the body. (Wiki 2025) Was this just a coincidence?
Studies confirmed a strong correlation, with a clear temporal link: mothers took thalidomide during early pregnancy when fetal limbs develop. Subsequent animal studies demonstrated that the drug disrupted development. By 1961, thalidomide was withdrawn from the market. The correlation wasn’t spurious; it was causal, with over 10,000 babies worldwide affected by its birth defects. This tragedy underscored that strong, consistent correlations, when supported by mechanistic evidence, can confirm causation and led to stricter drug safety regulations. (McBride 1961, Vanderbes 2023)

Smoking: From Correlation to Undeniable Cause
In the 1950s, researchers like Richard Doll and Austin Bradford Hill noticed a striking trend: heavy smokers were far more likely to develop lung cancer than non-smokers. Could genetics or urban living account for this difference? (Doll, R., & Hill, A. B. 1950s) Large-scale cohort studies tracked smokers and non-smokers over decades, carefully controlling for confounding variables like age and environmental factors. The correlation held. Furthermore, mechanistic evidence emerged: tobacco smoke contains carcinogens such as benzopyrene, which damage the DNA of lung cells. Animal studies and autopsies reinforced the link. By the 1964 Surgeon General’s report, the evidence was overwhelming: smoking causes lung cancer. “Smoking and Health: Report of the Advisory Committee to the Surgeon General held cigarette smoking responsible for a 70 percent increase in the mortality rate of smokers over non-smokers. The report estimated that average smokers had a nine- to ten-fold risk of developing lung cancer compared to non-smokers: heavy smokers had at least a twenty-fold risk. The risk rose with the duration of smoking and diminished with the cessation of smoking.” (U.S. Surgeon General 1964) This correlation, well-tested, fundamentally transformed public health and saved millions of lives.

Asbestos: A Slow-Burning Causal Link
Once hailed as a “miracle material” for its fire resistance, asbestos was widely used in industry. However, by the mid-20th century, workers such as miners and shipbuilders began to show a troubling correlation with lung diseases, including mesothelioma, a rare and aggressive cancer. Was asbestos to blame? Decades of research confirmed that inhaled asbestos fibers become trapped in the lungs, causing chronic inflammation and DNA damage. Higher exposure levels were directly linked to more severe health outcomes, and animal studies replicated these findings. By the 1970s, the link was undeniable, leading to regulations that protect workers. Nonetheless, asbestos’s legacy continues to haunt older buildings. Once more, correlation, backed by biological evidence, proved causation. (WHO 2024, Lucarelli (Ret) 2025, Asbestos 2024)

The historical cases of thalidomide, smoking, and asbestos demonstrate how rigorously examined correlations, using frameworks like the Bradford Hill criteria, can reveal crucial causal relationships that shape public health policies. These lessons underscore the need for thorough investigation into emerging concerns, such as reports of unusual fibrous amyloid clots (also described as a new type of Systemic Fibrinaloid Amyloid Coagulopathy (SFAC)) and myocarditis associated with mRNA COVID-19 vaccines, to distinguish between coincidence and true causation, ensuring well-informed decision-making.

Consideration: mRNA COVID-19 Vaccine

While not detailed above, recent concerns regarding unusual fibrous amyloid clots and myocarditis following mRNA COVID-19 vaccines should be critically evaluated with the same approach. Robust epidemiological studies and biological evidence are essential to determine whether the observed correlations imply causation. Researchers continue to study these events to distinguish true vaccine-related adverse effects from coincidental, unrelated occurrences in the general population.

When is Correlation Causal? The Bradford Hill Criteria
The Bradford Hill criteria offer a systematic framework to assess whether observed correlations can be interpreted as causal. These criteria include the following:

· Strength of Association: Strong correlations observed across different populations.

• Consistency: Similar findings across studies and regions.

• Specificity: The effect is tied to a specific cause, even if the cause is not exclusive.

• Temporality: The exposure precedes the outcome. A necessary condition for causality.

• Biological Gradient: Increasing levels of exposure lead to more severe outcomes.

• Plausibility: There is a biologically credible mechanism that explains the association.

• Coherence: The proposed causal link fits well with establishes scientific knowledge.

• Experiment: Altering the exposure results in changes in the outcome.

• Analogy: Similar effects have been observed in related contexts.

Historically, these criteria have been instrumental in transforming correlations into causal inferences. Notable examples, discussed in this Substack, include thalidomide induced birth defects, the established link between smoking and lung cancer, and the recognition of asbestos as a causal factor in mesothelioma. Each of these cases is characterized by consistent data, plausible mechanistic insights, and supportive experimental findings. Additionally, there are other unexplained findings, as illustrated in the following images:

Image 1 and 2: The images above are from a living patient who was reportedly in stable remission prior to receiving two vaccinations. He expelled these through his drain at home, and his medical team subsequently disposed of the drain tube waste

Unusual Fibrous Amyloid Clots and Myocarditis: Applying Bradford Hill to mRNA Vaccines
Since 2021, reports have emerged linking mRNA Covid-19 vaccines with unusual fibrous amyloid clots (SFAC) and myocarditis. These reports have spurred debate and concern. In this discussion, the Bradford Hill criteria is applied to determine whether these correlations suggest causation, drawing on surveys, such as those conducted by retired U.S. Air Force Major Thomas Haviland, and scientific studies.

Unusual Fibrous Amyloid Clots: A New Phenomenon?
Haviland’s surveys (2022–2024) of embalmers and the public respondents reveal a troubling trend. The companion People’s Blood Clot Survey gathers more than 1,400 self-reported and observed clotting cases from individuals across 40 countries, offering further insight into delayed clotting complications following vaccination.

2024 Worldwide embalmer blood clot survey key findings (Haviland 2022, 2023,2024, Dumais 2024, Hulscher 2025):

Respondents: 301 embalmers from multiple countries

· 83% (250 embalmers) reported seeing large, white, fibrous amyloid clots in corpses during 2024, up from 73% in 2023.

· These clots were found in an average of 27.5% of all embalmed bodies, up from 20% in the previous year.

· Most embalmers reported never encountering white fibrous clots before 2021, though some noted seeing this new type of clot in 2020. This correlation suggests that both the spike protein from the virus and the spike protein produced in greater quantities by the vaccine could enter the bloodstream and interact with fibrinogen, potentially contributing to clot formation.

· 78% also reported seeing signs of micro clotting, described as “dirty blood” or “coffee grounds”, in about 22% of cases, compared to less than 5% before 2020.

· Most embalmers acknowledged that their professional associations have never addressed this issue, despite high visibility in the field.

2024 People’s blood clot survey key findings (Haviland 2022, 2023,2024, Dumais 2024, Hulscher 2025):

Respondents: 1,425 individuals from over 40 countries findings:

• 1,294 individuals (91%) with clotting issues had received at least one COVID-19 vaccine dose.

• Only 79 clotting cases were reported in 2020 (pre-vaccine), compared to over 500 per year in 2021–2024.

• 26% of clotting cases occurred six months to over a year after injection, supporting theories of delayed-onset clot development.

• Most common clot locations: The legs, lungs, brain, and heart, precisely match CDC’s V-safe “free text” field analysis. Embalmers discovered these atypical, unusual structures in both arteries and veins."

• 257 individuals required surgical removal of clots; 242 individuals died from clot-related complications.

When evaluated through the Bradford Hill lens:

• Strength: Fibrous amyloid clots increased from nearly 0% pre-COVID to 27.5% of embalmed bodies in 2024, with 91% of public cases tied to vaccination.

• Consistency: Similar clotting patterns have been reported among embalmers in the U.S., Canada, the U.K., and Australia.

• Specificity: Although traditional clots have multiple potential causes, the fibrous amyloid clots appear to be a phenomenon unique to the post-2020 period.

• Temporality: The rise in clot reports followed the 2021 vaccine rollout, with a peak occurring 6–18 months thereafter.

• Biological Gradient: Preliminary data suggest that multiple vaccine doses may be associated with an increased prevalence of clotting.

• Plausibility: There is a potential mechanism where vaccines might trigger clotting via immune responses or the effects of the spike protein, although detailed mechanisms remain to be fully elucidated.

• Coherence: The escalating incidence of clots aligns with broader post-vaccination health reports, recognizing that COVID-19 itself can also induce clot formation.

• Experiment: Epidemiological observations indicate that declining booster uptake correlates with fewer reported clot cases in 2023–2024.

• Analogy: Notably, other vaccines (e.g., AstraZeneca) have been associated with clotting.

These findings are alarming, particularly considering the strong signals from temporality and consistency. However, reluctance within the medical community to acknowledge a direct link between clots and vaccines has, arguably, impeded further investigation.

Myocarditis: A Notable Risk
Myocarditis reports have also emerged post-vaccination. (Barda 2021, Mevorach 2021, Oster 2022, Patone 2022, Oster 2022, Witberg 2021) Applying Bradford Hill:

• Strength: Studies indicate higher myocarditis rates in the vaccinated compared to unvaccinated populations.

• Consistency: Data from sources such as VAERS, EudraVigilance, and studies from Israel consistently show elevated myocarditis rates after vaccination, especially following the second dose. (Bozkurt 2021)

• Specificity: While myocarditis can result from several causes (including COVID-19 itself), the incidence pattern post-vaccination, especially in young males, is distinctive. (Witberg 2021)

• Temporality: Cases of myocarditis typically occur within days to one week after vaccination. (Bozkurt 2021, Oster 2022)

• Biological Gradient: There is a higher risk observed after the second dose compared to the first dose. (Note: Read Table 2 of this reference: Bozkurt, B., Kamat, I., & Hotez, P. J. (2021). Myocarditis With COVID-19 mRNA Vaccines. Circulation, 144(6), 471–484. https://doi.org/10.1161/CIRCULATIONAHA.121.056135)

• Plausibility: One hypothesis is that the spike protein might trigger an inflammatory cascade in the heart through an overactive immune response or via molecular mimicry. Studies support this view:

  • Schreckenberg et al. (2024) reported that mRNA vaccines affect rat cardiomyocytes differently, with Moderna associated with arrhythmic contractions and Pfizer linked to increased protein kinase A activity, suggesting a possible cardiac side-effect mechanism .

  • Krauson et al. (2023) demonstrated that vaccine mRNA can be detected in the myocardium up to 30 days post-vaccination .

Fig 1 SARS-CoV-2 vaccine in the heart is associated with healing myocardial injury at the time of vaccination and macrophage infiltration in the myocardium. Krauson (2023)

• Coherence: The pattern of myocarditis post-vaccination fits into the broader context of cardiac issues noted with other immunizations, although COVID-19 itself is known to cause myocarditis. (Note: mRNA vaccine is based on the genetic sequence of COVID-19 with a modified nucleotide. Nance 2021 )

• Experiment: Evidence indicates that extending the interval between vaccine doses reduces the myocarditis risk, which supports a potentially modifiable link.

“Data specific to men aged 18-29 years indicated that the dosing interval might need to increase to ≥56 days to substantially drop myocarditis or pericarditis incidence.” (Pillay 2022)

• Analogy: Similar mechanisms of myocarditis have been observed with other vaccines and infections. Furthermore, Nakahara et al. (2023) found that vaccinated individuals exhibit increased myocardial 18F-FDG uptake for up to 180 days post-vaccination, pointing toward a physiologic response in the heart .

Why This Matters Today

Historical events have shown that when multiple strands of evidence align, ranging from consistent epidemiological data to robust mechanistic studies, correlation can indeed signify causation. The thalidomide tragedy led to fundamental changes in drug regulation, the link between smoking and cancer galvanized public health campaigns, and asbestos bans have safeguarded workers for decades.

In the case of mRNA vaccines, the data on myocarditis and clotting show strong signals in temporality, consistency, and plausibility. However, there remain gaps, particularly concerning specific mechanistic insights and controlled experimental data. An added complexity is that COVID-19 itself can lead to similar adverse outcomes, which muddies issues of specificity.

It is critical to avoid misinterpreting correlations, as doing so can lead to inappropriate policy decisions or unwarranted public panic. The overarching lesson is to rigorously evaluate the evidence, challenge assumptions, and demand high-quality studies. The unusual fibrous amyloid clot reports, in particular, deserve urgent and thorough investigation given their unprecedented nature and severe clinical outcomes. Unfortunately, a certain reticence in the medical community, possibly due to fear of backlash, has slowed the pace of further inquiry.

My Suggestions

The distinction between correlation and causation remains a critical challenge in scientific debates. Have you encountered instances where these concepts were misinterpreted, leading to flawed conclusions? Applying rigorous analytical frameworks like the Bradford Hill criteria can provide clarity, ensuring complex issues are properly examined.

Keeping the conversation alive around data, assumptions, and evidence is essential for strengthening public health policies and maintaining scientific integrity.

Additionally, understanding key biological mechanisms is crucial in evaluating emerging concerns. Amyloidogenic refers to the ability of certain proteins to misfold and aggregate into amyloid fibrils, contributing to various diseases. These misfolded proteins interfere with normal cellular functions, potentially leading to conditions such as amyloidosis and neurodegenerative disorders.

Likewise, Atypical Fibrinogenic describes an abnormal composition of fibrinogen sheets, where the ratios deviate from typical physiological patterns. Recognizing these deviations helps differentiate normal biological processes from pathological ones.

Due to these concerns, we must halt the mRNA vaccine to ensure public health and safety.

References

Asbestos Exposure and Cancer Risk Fact Sheet, NCI (nciglobal,ncienterprise). (2024, August 15). [cgvArticle]. https://www.cancer.gov/about-cancer/causes-prevention/risk/substances/asbestos/asbestos-fact-sheet

Barda, N. et al. Safety of the BNT162b2 mRNA Covid-19 vaccine in a nationwide setting. N. Engl. J. Med. 385, 1078–1090 (2021).

Bozkurt, B., Kamat, I., & Hotez, P. J. (2021). Myocarditis With COVID-19 mRNA Vaccines. Circulation, 144(6), 471–484. https://doi.org/10.1161/CIRCULATIONAHA.121.056135

DOLL, R., & HILL, A. B. (1950). Smoking and carcinoma of the lung; preliminary report. British medical journal, 2(4682), 739–748. https://doi.org/10.1136/bmj.2.4682.739

Dumais, JM (2024, Jan 22). Exclusive: 70% of Embalmers Report Finding Strange Blood Clots Beginning in Mid-2021. Children’s Health Defense. Retrieved June 3, 2025, from https://childrenshealthdefense.org/defender/blood-clots-embalmers-report-mid-2021-covid-vaccines/

Haviland, T (2022, 2023, 2024). Survey can be found:

Results of the 2024 Worldwide Embalmer Blood Clot Survey

Hulscher, N. (2025, May 16). Worldwide Embalmer Survey Reveals Striking Rise in White Fibrous Clots Following COVID-19 Vaccination.

Worldwide Embalmer Survey Reveals Striking Rise in White Fibrous Clots Following COVID-19 Vaccination

Krauson, A. J., Casimero, F. V. C., Siddiquee, Z., & Stone, J. R. (2023). Duration of SARS-CoV-2 mRNA vaccine persistence and factors associated with cardiac involvement in recently vaccinated patients. NPJ vaccines, 8(1), 141. https://doi.org/10.1038/s41541-023-00742-7

Lucarelli, J. (n.d.). Banning Asbestos | U.S. History, Progress & Laws. Mesothelioma.Com. Retrieved June 4, 2025, from https://www.mesothelioma.com/lawyer/legislation/asbestos-ban/

McBride, W. G. (1961). Thalidomide and congenital abnormalities. The Lancet, 2(7216), 1358. https://doi.org/10.1016/S0140-6736(61)90927-8 https://www.softenon.nl/uploaded/Library/BriefMcBride_TheLancet19611216.pdf

Mevorach, D., Anis, E., Cedar, N., Bromberg, M., Haas, E. J., Nadir, E., Olsha-Castell, S., Arad, D., Hasin, T., Levi, N., Asleh, R., Amir, O., Meir, K., Cohen, D., Dichtiar, R., Novick, D., Hershkovitz, Y., Dagan, R., Leitersdorf, I., Ben-Ami, R., … Alroy-Preis, S. (2021). Myocarditis after BNT162b2 mRNA Vaccine against Covid-19 in Israel. The New England journal of medicine, 385(23), 2140–2149. https://doi.org/10.1056/NEJMoa2109730

Nakahara, T., Iwabuchi, Y., Miyazawa, R., Tonda, K., Shiga, T., Strauss, H. W., Antoniades, C., Narula, J., & Jinzaki, M. (2023). Assessment of Myocardial ¹⁸F-FDG Uptake at PET/CT in Asymptomatic SARS-CoV-2-vaccinated and Nonvaccinated Patients. Radiology, 308(3), e230743. https://doi.org/10.1148/radiol.230743

Nance, K. D., & Meier, J. L. (2021). Modifications in an Emergency: The Role of N1-Methylpseudouridine in COVID-19 Vaccines. ACS Central Science, 7(5), 748–756. https://doi.org/10.1021/acscentsci.1c00197

Oster ME, Shay DK, Su JR, et al. Myocarditis Cases Reported After mRNA-Based COVID-19 Vaccination in the US From December 2020 to August 2021. JAMA. 2022;327(4):331–340. doi:10.1001/jama.2021.24110

Patone, M., Mei, X.W., Handunnetthi, L. et al. Risks of myocarditis, pericarditis, and cardiac arrhythmias associated with COVID-19 vaccination or SARS-CoV-2 infection. Nat Med 28, 410–422 (2022). https://doi.org/10.1038/s41591-021-01630-0

Pillay J, Gaudet L, Wingert A, Bialy L, Mackie A S, Paterson D I et al. Incidence, risk factors, natural history, and hypothesised mechanisms of myocarditis and pericarditis following covid-19 vaccination: living evidence syntheses and review BMJ 2022; 378 :e069445 doi:10.1136/bmj-2021-069445

Schreckenberg, R., Woitasky, N., Itani, N., Czech, L., Ferdinandy, P., & Schulz, R. (2024). Cardiac side effects of RNA-based SARS-CoV-2 vaccines: Hidden cardiotoxic effects of mRNA-1273 and BNT162b2 on ventricular myocyte function and structure. British journal of pharmacology, 181(3), 345–361. https://doi.org/10.1111/bph.16262

The History of Asbestos Regulation in the US. (n.d.). Eurofins Scientific. Retrieved June 4, 2025, from https://www.eurofinsus.com/environment-testing/built-environment/resources/recent-news-blogs/blog-the-history-of-asbestos-regulation-in-the-us/

U.S. Surgeon General The 1964 Report on Smoking and Health. (2019, March 12). Reports of the Surgeon General - Profiles in Science. https://profiles.nlm.nih.gov/spotlight/nn/feature/smoking

WHO 2024., Asbestos. (27 September 2024). Retrieved June 4, 2025, from https://www.who.int/news-room/fact-sheets/detail/asbestos

Witberg, G., Barda, N., Hoss, S., Richter, I., Wiessman, M., Aviv, Y., Grinberg, T., Auster, O., Dagan, N., Balicer, R. D., & Kornowski, R. (2021). Myocarditis after Covid-19 Vaccination in a Large Health Care Organization. The New England journal of medicine, 385(23), 2132–2139. https://doi.org/10.1056/NEJMoa2110737

Vanderbes, J. (2023, July 26). Sixty Years ago, a Series of Mysterious Birth Defects Spurred A Search For Answers. National Endowment for the Humanities. https://www.neh.gov/article/series-mysterious-birth-defects-spurred-search-answers