I recently saw someone post this NSFW screenshot image about vaccines in a discussion about the COVID-19 outbreak. It is a screenshot from this NSFW 4chan thread.

The anonymous poster argues that childhood diseases prevent cancer:

The more the immune system is trained to mount Th2 responses to infectious agents, the less the immune system is capable of mounting Th1 responses. Why is this important? The literature is packed with peer-reviewed research that conclusively proves that infection with childhood illnesses reduces cancer risks later in life. Why? The immune system is being actively trained to have strong Th1 responses to anything that looks weird. Failure to contract childhood illnesses leaves the body less equipped to deal with weird shit, and thus cancer is more likely to take root.

The poster goes on to deny that such a protective effect arises from vaccinations:

So ... wouldn't vaccination cause this same response? [F**K] NO. NEVER. This is why understanding the immune system is critical to understanding the vaccine debate: vaccines inevitably cause ONLY a Th2 response by the immune system. The point of vaccines is to generate antibody-producing memory B cells, so the next time the immune system is presented with the antigen from the vaccine, antibodies can be produced. It is ABSOLUTELY CRITICAL to understand that this in no way protects the body in the same way as an acute, natural infection, and in no way prevents an acute infection from the source of the antigens if the humoral immune system gets overwhelmed. Should this happen, the vaccinated individual is less-equipped to handle the infection than an individual that is totally naive to the infectious agent, as Th1 immunity has been actively stunted and suppressed. Furthermore, even if the humoral (Th2) response is sufficient to stymie acute infection from a programmed antigen, the immune system of vaccinated individuals will be less able to mount an effective Th1 response to any infection that they body has not been programmed to recognize.

Is this true? It seems to pass the woo sniff test. Many of their statements (but perhaps not this one) are backed up with links to the NIH website.

I'm not a doctor, so I'm unfamiliar with the science. Does being vaccinated against childhood illnesses leave the immune system less able to tackle cancer?

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    If you want the full details, biology.se would be more likely to be helpful. Feb 2, 2020 at 12:00
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    The gaping hole in the thread's logic is the implication that it's not the common cold and minor everyday infections that children's immune systems train themselves with, but the major, life-threatening diseases that vaccines prevent, like rubella, polio and measles. But I'm not sure how to go about disproving something so obvious with answer-quality evidence - has anyone bothered making a study proving that the common cold is still just as common in children vaccinated against other unrelated illnesses? Feb 2, 2020 at 15:04
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    There is a school of thought that reduced early immune activity increases leukaemia risk, but the target is excessively sterile environments which prevent children being routinely exposed to minor everyday infections, bugs and sniffles. Saying children shouldn't be vaccinated against potentially fatal infections because everyday, minor infections develop the immune system and reduce leukaemia risk is like saying bumps and bruises toughen children up, therefore, they shouldn't merely play outside more, they should also step out in front of traffic. Feb 2, 2020 at 15:07
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    There is what's known as the "sanitation hypothesis", the supposition that being raised in relatively sterile environments makes people more susceptible to diseases such as polio. And the parallel "hygiene hypothesis" that supposes that being raised in a relatively "non-challenging" environment makes one more susceptible to asthma. Both of these have some merit, according to the experts, but the arguments can be taken too far. Feb 2, 2020 at 19:58
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    Well, I wouldn't take 4chan seriously enough to even wonder if it was correct ...
    – RedSonja
    Feb 3, 2020 at 14:40

1 Answer 1



There are many debunked claims about possible dangers of vaccines in this 4chan thread, including the old standby that vaccines cause autism, which is dealt with in this Skeptics Q&A. I will address the specific claim discussed in the OP. It has a few parts:

  1. Acute infections with wild type pathogens produce a Th1 response, but vaccines can only produce a Th2 response
  2. Because of this, getting vaccinated makes people more susceptible to cancer


The claim is false.

For the first part of the claim, measles provides an excellent counter example. By it's very nature, infection with the wild type virus involves immune escape by inducing a Th2 response, and the vaccine has a confirmed Th1 response. Because the claim is absolute (no vaccines produce a Th1 response), the fact that the measles vaccine has a confirmed Th1 response is sufficient to show the claim is false.

The second part of the claim depends on the first, but I also address the evidence provided by the claimant below in the section on evidence. To summarize, the thread provides only one direct piece of evidence, which, in fact, shows a reduced risk of cancer for vaccinated individuals. Of note, there are vaccines that specifically prevent cancer because they prevent an infection that causes cancer. The best data here is for HBV, which I discuss briefly in the section on evidence.

Broadly, the arguments used to support the claims are based on a misunderstanding of the way the immune system works, the claim itself is absolute and readily falsifiable, and the evidence cited to support the claims is either misrepresented or poor.


The claim has some substantial misunderstandings about how the immune system works, which makes it a little tricky to systematically debunk without giving a great deal of detail, but I will try to hit the key points without getting lost in the weeds.

A key part of this claim involves the differentiation of naive CD4+ T-cells (helper T cells) into effector cells. This is generally textbook level stuff. In order of increasing complexity, I recommend Sompayrac's How the Immune System Works (Ch 6 discusses differentiation into effector cells), or Abbas Basic Immunology (Ch 5), or Janeway's Immunobiology (Ch. 9).

Differentiation of CD4+ T-cells

Cd4+ T-cells differentiate into one of several types of effector cells based on host and antigen properties at the time of activation. It is true that there is a T-helper 1 profile, and a T-helper 2 profile. There are also others, and (same reference) there is evidence that cells that have differentiated into one type may change types. The distinction between the different CD4+ T cells is based on the profile of cytokines they secrete. The classic Th1 and Th2 profile are based on the discovery of separate profiles in mouse experiments. The relevant profiles for this claim are T-helper 1 and T-helper 2. The cytokine IFN-gamma is specific for Th1. IL-4, IL-5, and IL-13 are specific for Th2.

To my reading, it seems the author of the thread has confused Th1 and Th2 profiles for CD4+ and CD8+ T-cells, so I want to be clear that Th1 and Th2 cells are types of CD4+ T-cells. The primary role for CD4+ T cells is to control the immune response, to decide which cells to use for a particular immune response, and what exactly they should do. Sompayrac uses the analogy of a quarterback. They do this through different cytokine profiles. Different cytokines will tell different cells to do different things.

The thread mentions CD8+ T cells as well. The primary role for CD8+ T cells is to directly attack intracellular pathogens. CD8+ T cells can be activated by CD4+ T cells, but they can be activated by other cells. Similarly, CD4+ T cells can use CD8+ T cells to attack intracellular pathogens, but they can also use other cells, e.g., macrophages and other phagocytes.

Importantly, differentiation into effector T-cells does not occur until after a naive T-cell is activated (by recognizing its cognate antigen in the presence of a costimulatory signal). The fact that differentiation occurs during and after activation of naive CD4+ cells is important here, so I will quote


After recognizing pathogen peptides presented by MHC class II molecules, naive CD4 T cells can differentiate down distinct pathways that generate effector subsets with different immunological functions. The main CD4 effector subsets are Th1, Th2, Th17, and Tfh, which activate their target cells; and regulatory T cells, or Treg cells, which inhibit the extent of immune activation.

We continue to maintain a pool of naive T-cells even in old age. Tumor antigen recognition by a T-cells starts when a naive T-cell recognizes its cognate antigen, either a mutated self peptide presented by a MHC class I molecule to a CD8+ T-cell, or a mutated self peptide that has been digested by an antigen presenting cell and presented on a MHC class II molecule to a CD4+ T-cell. Differentiation into one of the various T-helper types (in the case of the CD4+ T cell) is determined by the milieu in which recognition occurs. Abbas Ch. 10 provides a good introductory review of this process in the context of cancer. The point here is that these aren't previously activated, previously differentiated T-cells that have recognized childhood infections or childhood vaccines. They are naive T-cells with specific T-cell receptors. Those specific T-cell receptors have a cognate antigen that happens to be a tumor antigen, rather than e.g., a measles antigen. Just like every other naive T-cell, they have been sitting around since they initially developed in the thymus and are now recognizing that cognate antigen for the first time.

Acute infections with vaccine preventable diseases can produce Th2 responses, and vaccines can produce Th1 response

A key argument in this claim is that all acute infection produces Th1 response, while all vaccination produces a Th2 response.

Wild type measles infection produces a Th2 response

One of the reasons the measles virus is so successful is because it has a number of strategies to escape immune detection. A Th1 mediated immune response is required to clear a wild type infection. The virus attempts to escape clearance by inducing a Th2 response, effectively tricking the immune system into thinking it has an infection that requires a Th2 response. See Murray Medical Microbiology, Ch 58:

Measles depresses the immune response by (1) directly infecting monocytes and T and B cells and (2) by promoting a switch from the Th1 associated interferon gamma and IL12 cytokines to the production of Th2 associated cytokines, especially interleukin 4 (IL4), Il5, IL10, and IL13.

If you prefer the primary literature, see: https://www.ncbi.nlm.nih.gov/pubmed/8101549/

The measles vaccine produces a Th1 response

The claim states:

So ... wouldn't vaccination cause this same response? FUCK NO. NEVER. This is why understanding the immune system is critical to understanding the vaccine debate: vaccines inevitably cause ONLY a Th2 response by the immune system

If this is true, there should be no counter example.

The MMR vaccine is a combined measles, mumps, and rubella vaccine given to children beginning at 12 months of age in the United States. The measles component is a live attenuated measles strain known as Edmonston Enders. One of the ways this vaccine is attenuated is by removing the ability to induce a Th2 response. Vaccination thus produces a Th1 response, as confirmed here

This Mayo clinic study is particularly useful here. This group studied the cytokine profiles of T-cells from individuals with documented MMR vaccination (Edmonston-Enders) strain and no record of wild type measles or exposure to wild type measles. It demonstrates that re-exposure of these T-cells to the attenuated strain (vaccine) produces a Th1 response, while exposure to wild type measles does not.

Evidence provided in the thread is limited, poor quality, or completely misrepresented

Evidence provided by the claim's source

The thread attempts to demonstrate the legitimacy of the claim with a number of links to literature. However, there is only one citation regarding an association between vaccines and cancer. The citation does not, in fact, support the claim.


Children who received 3 or more doses of hepatitis B vaccines had a significantly increased risk of leukemia (OR = 2.6). Infants who receved hepatitis B vaccines were approximately 5 times more likely to develop leukemia. https://www.ncbi.nlm.nih.gov/pubmed/15951359

Citation states:

The citation states the opposite. Specifically, it states HBV vaccination is not associated with leukemia risk.

The OR for hepatitis B vaccination (ever/never) was 0.76 (95% CI 0.36–1.59) ...

The number of doses of hepatitis B vaccine received was not associated with leukaemia risk.

From the table, those who received 3 or more doses of HBV during infancy did have an OR > 1, but it was not significant.

1.41 (0.90, 2.20)

Importantly, there are 14 comparisons reported here, and the only significant associations were in the opposite direction (vaccination was associated with a reduced risk of cancer) and for Haemophilus influenzae vaccination (Hib)

Compared with children who received two or fewer doses of Hib vaccine, those who received three or more doses had a significantly reduced risk of childhood leukaemia (odds ratio = 0.55, 95% confidence interval 0.32-0.94)

Of note, the HBV vaccine is one of the few vaccines that both has a direct effect of preventing cancer and has been around long enough for direct evidence of that effect. Heptatis B virus is an important cause of hepatocellular carcinoma, and vaccination is protective.

So, the one study cited by the thread to give evidence of vaccines causing cancer does not actually show that. The thread says HBV vaccination is led to a 5 fold increase in the risk of leukemia. The study shows no significant association between HBV and leukemia. The only significant association in the study between vaccination and leukemia is that Hib vaccination is associated with a reduced risk of childhood leukemia, and vaccination against HBV has a direct benefit of preventing liver cancer (HBV infection being an important cause of liver cancer).

Indirect evidence provided by the claim's source

The thread also cites a 1998 case control study of patients of anthroposophic medicine practitioners that reports an association between patient recall of febrile childhood illnesses and cancer risk. This study does not provide good evidence for the claim that vaccination impairs the immune systems ability to fight cancer. In addition to not comparing vaccinated and unvaccinated individuals, this study has a number of methodological problems, most importantly, it uses adult recall of childhood illnesses to measure exposure, and the subjects are a convenience sample. Since individuals who decide to see an anthroposophic medicine practitioner are more likely to believe that childhood fevers prevent cancer, there are important selection and recall bias effects here.

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    @DeNovo this answer is epic - the quality and citations are spot on. You are why I keep coming back to skeptics :-) Feb 12, 2020 at 9:50

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