Let’s look at vaccine issues and objections; first acknowledging that vaccination has been the greatest medical advance since modern sanitation (including purifying drinking water).
First, modified viruses or cross reactivity of close viral (less pathogenic) relatives were the first vaccines, smallpox and rabies. Smallpox vaccine virus, vaccinia origins are fuzzy, cowpox, extinct horse pox, or weakened smallpox virus? Vaccination started with variolation, an obsolete medical procedure involving the inoculation of a susceptible person with material from the pustules of a smallpox patient to induce a mild form of the disease and hopefully confer immunity. Lady Mary Wortley Montagu, who had witnessed the practice in Turkey, introduced variolation to Britain in the early 18th Century. Benjamin Franklin was also a strong advocate for variolation, even having his own son variolated. Catherine the Great, Empress of Russia, played a significant role in promoting variolation within Russia. Variolation was not without risks. There was a chance of contracting a severe form of smallpox, and some individuals died from the procedure. Variolated individuals could still transmit smallpox to others.
The Jenner vaccine eliminated the former problem but vaccinia could still be transmitted by contact from a vaccinated person to a naive one. On very rare occasion (particularly with an immune suppressed patient) could lead to systemic disease. Edward Jenner postulated that the pus in blisters from sufferers of cowpox (a disease similar to smallpox but much less virulent) protected them from smallpox. On 14 May 1796, Jenner tested his hypothesis by inoculating James Phipps, the eight-year-old son of Jenner’s gardener. He scraped pus from cowpox blisters on the hands of Sarah Nelmes, a milkmaid who had caught cowpox from a cow called Blossom (whose hide now hangs on the wall of the St George’s Medical School library, in Tooting, London).
Even then, people objected to vaccination, like now for exaggerated, often irrational reasons: Some members of the Church believed that disease was sent by God, so the vaccine interfered with God’s will. The vaccine worked by giving people an animal disease. Some people felt that this was not safe and that vaccinated people would grow horns. Although the vaccine has lead to the first and only elimination of an infectious disease in humans (now the niche is being filled by Mpox) we still hear these kind of stange objections. Smallpox was officially declared eradicated on May 8, 1980, by the World Health Organization (WHO). The last known case of natural smallpox infection occurred in Somalia in 1977.
The second elimination of an infectious disease by vaccination was one in cattle, Rinderpest. It was a highly contagious and fatal disease of cattle and other ruminants. It was declared eradicated globally in 2011. This achievement, the second disease to be eradicated after smallpox, was the culmination of a decades-long effort, primarily through the Global Rinderpest Eradication Programme (GREP). The eradication of rinderpest is considered a significant milestone in the field of animal health and a major contribution to global food security and livelihoods.
The production and application of a live whole attenuated vaccine did not always give expected immunity, regardless of its closeness to the original virulent form. Originally, in France, Pasteur and his successors had developed four such anthrax vaccine strains administered in the numerical order of I-IV, with IV being equivalent to wild type fully pathogenic anthrax. At times serum from immune animals was administered in conjunction with the anthrax vaccine. All the strains were administered as vegetative forms and, therefore, were unstable for field use, conferring various levels of immunity and often not halting anthrax outbreaks at all. What was needed was a very stable vaccine that did not require cooling and could endure the conditions of the South African pasture lands as well as the natural disease bacillus.
In 1922, they started using a spore vaccine like one first invented in Australia by amateur bacteriologists John Gunn and John MacGarvie-Smith during the 1890s. It was designed to overcome deterioration during long-term storage and transportation at elevated temperature by exploiting the natural heat-resistant spores. More effective than Pasteur’s vaccine, under severe field conditions, spore vaccines were in widespread use in America, Australia and Japan by the early 1920s. They were first produced at Onderstepoort about the same time.
However, they failed to be protective, demonstrated by failures in the field in 1926 and 1933. An attenuated strain that killed susceptible guinea pigs but not rabbits and provided protection for the latter was required in the laboratory to be considered a vaccine candidate. Heating the cultures to 42°C during culture was considered the way to generate the attenuated vaccine strains. However, this approach is what produced the mixed results experienced in 1926 and 1933.
Max Sterne, an Onderstepoort-trained veterinary scientist and bacteriologist, appointed in 1934 to manage vaccine production, decided to take up the challenge of overcoming these setbacks. Sterne thought previous researchers had missed the potential significance of the link of the virulence of Bacillus anthracis to the ability of the organism to form a “capsule” over the cell wall, which allowed it to evade destruction by phagocytic white blood cells. In the course of propagating a series of these smooth variants, those making capsule, in his attempts to produce immunity, he discovered unencapsulated “rough” mutants. Sterne cited German studies done around 1910, which indicated unencapsulated forms of naturally occurring Bacillus anthracis could sometimes produce immunity. Guinea pigs injected with the unencapsulated, aviru-lent “disassociants” of certain strains were shown to be able to resist very large doses of a highly virulent strain. These results raised the possibility that a completely avirulent vaccine with the stability of previous spore vaccines could solve the problem of safety. A method of consistently producing encapsulated smooth colonies out of which rough mutants could be picked was required.
Sterne theorized that the characteristic roughness of otherwise virulent strains obtained from dead animals might be an adaptation to the culture conditions in the laboratory. The conditions under which Bacillus anthracis normally multiplied, however, were found in the bloodstreams of living animals. Encapsulated smooth cultures might be obtained more easily under conditions which emulated the natural environment for the propagation of the bacteria in the animal body. One of Sterne’s colleagues, the British bacteriologist J. H. Mason, constructed a tube containing a semi-solid medium of horse serum and agar in which the concentration of carbon dioxide could be controlled.
Using this innovation, Sterne found he could easily grow encapsulated smooth variants which regularly produced visible colonies of mutants of rough unencapsulated bacilli. These unencapsulated variants all turned out to be avirulent when injected into guinea pigs and some gave a good degree of protection against the injection of virulent cultures.
He eventually chose an unencapsulated variant of a strain isolated from a severe outbreak, designated 34F2. To produce the vaccine, bacilli were picked from the rough colony, allowed to sporulate, and then freeze-dried. When vaccine was needed, the manufacturer germinated the spores and propagated them in large quantities on solid agar. These cultures were then allowed to sporulate in oxygen and washed off into saline at a standard concentration for division into individual doses.
The avirulent nature of the new vaccine was very important because it now im-munized, rather than killed guinea pigs,
making them useful for testing the level of protection produced by the vaccine.
Furthermore, these results for the guinea pig were predictive for large animals, so there was no longer the need for expensive large-scale testing on sheep. Initially a small number of animals were injected in the field to check that the vaccine produced no severe reactions. Vaccine derived from strain 34F2 was used for all animals (this strain still killed mice), but smaller doses were used for horses and goats. The “avirulent” vaccine was first released for field trials in 1936 and used on a large scale beginning in 1938. This vaccine is still used today globally for large animals.


For anthrax, like many modern vaccines such as DPT for other bacterial diseases, the antigen the vaccine is actually effective against is the toxin rather than the bacterium itself, and toxoids (“detoxified” toxins must be included in the vaccine such as for diphtheria and tetanus and, in part, pertussis) are included in the vaccines.
The pXO1 and pXO2 plasmids in Bacillus anthracis, which are crucial for its virulence, were discovered in the late 1980s and early 1990s. Specifically, pXO1, which carries the genes for anthrax toxins, was identified by Makino et al. in 1989. It is still in the Sterne vaccine strain. The pXO2 plasmid, which encodes the capsule that protects the bacteria from the host’s immune system, was identified by Reif et al. in 1994 was eliminated from the Sterne strain making reversion to a pathogenic one impossible. PA is the key targetted antigen to block both anthrax toxins and confer protective immunity by the vaccine.
The live virus vaccine objections have had some merit due to mutation reversion in attenuated oral polio vaccine (now replaced by killed vaccine, but with still some persistence of the live oral less pathogenic strain, due to prior use, in certain populations in other countries, spread through contaminated water and poor sanitation). Other live vaccines have been removed because of reversion to pathogenic forms, or on rare occasion, failure to provide sufficient protection from wild type disease. Examples being modified live rabies vaccine which gave strong protection in dogs but could revert to cause rabies in cats and primates, Venezuelan Equine Encephalitis live vaccine (TC83) that could revert, cause fever, or fail to protect because the attenuated form had so few genetic changes and the very simple genome of the pathogenic form, Strain 19 Brucella vaccine in cattle because it persisted in cattle as a low-grade infection, causing false positives on brucella tests, and because it caused brucellosis in humans (accidentally self-inoculated). Strain 19 was replaced by RB51 Brucella vaccine to avoid the false positives and human disease. There have been less human infections. but still a few.
The Johnson & Johnson Adenovirus vaccine is a non-replicating COVID spike-gene-containing virus that induces synthesis of the COVID spike protein from copy DNA inserted in its genome. Other viruses used to make desired vaccine proteins from nucleic acid templates include canary pox virus (in vaccines for canine distemper virus, feline leukemia virus, or West Nile virus). and modified retroviruses (vaccine platform specifically aimed at inducing immune responses against Hepatitis C Virus (HCV) antigens displayed by recombinant retrovirus-based virus-like particles (VLPs) made of Gag protein of murine leukemia virus). Naked DNA vaccines delivered by nanoparticles or electroporation have also been made but are less popular. DNA vaccines have been approved for use in certain animal diseases, such as West Nile Virus in horses and melanoma in dogs. They are also being developed for Human Immunodeficiency Virus (HIV) and Cancer: Research is ongoing to explore the potential of DNA vaccines for these diseases. The DNA must be transcribed into messenger RNA (mRNA) then translated into proteins to be immunogenic. This is true for all live virus vaccines and carrier virus vaccines,
DNA and mRNA vaccines must have the protein antigens expressed from nucleic acid templates to be immunogenic and protect against infectious diseases. Their advantage compared to attenuated or carrier viruses is they have no proteins, except those expressed after administration. Like live vaccines they do not deliver a finite amount of antigen or just protein as killed vaccines do. The nucleic acid vaccines (DNA or mRNA) can only deliver immunogens they are programmed for. They have finite life times in host cells and mRNA is even more fragile than DNA because of the arsenal of enzymes in cells to destroy RNA even with modifications to delay them. mRNA do not need to travel to the nucleus, like DNA, to be translated into the protein antigens.
Another concern is preservatives and adjuvants. Preservatives such as antibiotics and thimerosal (thio ethyl mercury) are necessary because the viruses for vaccines are grown in cell culture or embryonated chicken eggs (standard influenza vaccines which may become contaminated with bacteria that can grow alongside the viruses in production or after bottling and produce products such as endotoxin that are harmful even at low concentrations.)
The claims of toxicity are because of confusing different compounds of mercury, like methyl mercury which is more toxic than ethyl mercury. Mercuric chloride has been used in medicine as an antiseptic and syphilis treatment, its toxicity and corrosive nature led to its discontinuation in modern medical practice. All compounds of mercury are not equivalent in toxicity.

Adjuvants have been blamed for a variety of adverse effects of vaccination through induction of chronic inflammation (linked to cancer in humans in general, other mammals, and, particularly, in cats through injection site fibrosarcomas). However, they are necessary to achieve robust immune responses to vaccines by triggering the non-specific innate response which then triggers a specific immune response that supersedes innate responses and suppresses the former when adequate specific immunity is achieved. Among the most commonly used ones are:
Aluminum Salts (Alum):
These are the most widely used adjuvants in human vaccines, found in
vaccines for hepatitis A, hepatitis B, and others. They are known to promote
a Th2-biased immune response, which is important for antibody production.
Oil-in-water emulsions:
MF59 and AS03 are examples, composed of squalene, polysorbate 80, and other components. They are used in influenza vaccines and other vaccines.
These emulsions can prolong antigen exposure and enhance antigen
presentation.
Saponins:
These natural compounds, found in the bark of the Quillaja saponaria tree,
are used in adjuvants like Matrix-M™, which is used in the R21/Matrix-M
malaria vaccine. Saponins stimulate both humoral and cellular immune
responses.
TLR Agonists:
These adjuvants mimic pathogen-associated molecular patterns (PAMPs)
and activate Toll-like receptors (TLRs), triggering immune responses. CpG
1018, a TLR9 agonist, is used in some vaccines.
In humans, up until the 1960’s, no virus was thought to cause cancer. Epstein-Barr virus (EBV) was first discovered in 1964, in Burkitt lymphoma cells. Researchers Anthony Epstein, Yvonne Barr, and Burt Achong identified the virus in a cell line derived from a patient with Burkitt lymphoma. This discovery marked the first time a human virus was shown to be associated with cancer. However, it does not always cause cancer, lymphoma appearing predominantly in children, causing “Kissing Fever”, mononucleosis in youths and adults. A breakthrough vaccine against a virus that causes cancer in humans was developed in 2006. The Human Papillomavirus (HPV) vaccine is a vaccine that protects against infection by certain types of HPV and protects against several types of HPV that can cause cervical, vaginal, vulvar, penile, anal, and oropharyngeal cancers. It also prevents genital warts caused by certain HPV types. The CDC recommends routine vaccination for adolescents starting at age 9-12, and it can be given up to age 26 for those not previously vaccinated or with a weakened immune system. The HPV vaccine has been shown to significantly reduce HPV infections, genital warts, and precancerous cervical changes. ACOG recommends it as an important tool for cancer prevention, and it is recommended that healthcare providers increase vaccination rates.
Lipid nanopa!icles:
These are used extensively in mRNA vaccines to deliver the mRNA and also
have an adjuvant effect, enhancing the immune response.
Amongst these, aluminum has been attacked the most recently by those who oppose vaccination, especially of children but this accusation has not stood up to the data and scientific analysis.
The most notorious adjuvant historically is Freund’s Adjuvant, only used in research in mice and rats and other research animals to experimentally induce a strong immune response. Freund’s adjuvant is a water-in-oil emulsion that helps prolong the release
of antigens, leading to a stronger and longer-lasting immune
response. It is named after Jules T. Freund, who developed it in the 1940s. Complete Freund’s Adjuvant includes heat-killed mycobacteria (like Mycobacterium tuberculosis) in addition to the oil emulsion. Freund’s adjuvants are not for human or veterinary use. CFA can cause significant side effects, including infammation, pain, and granulomas.
The most notorious example of vaccine adjuvant associated reactions is in cats, injection site fibrosarcomas. Feline injection-site sarcoma specifically denotes a type of cancer, often linked to injections (FISS). While adjuvants are crucial for vaccine efficacy, they can also trigger inflammation at injection sites, and in some predisposed cats, this inflammation may contribute to the development of FISS. The link is tenuous as vaccine causative because of the often long delay in the cancer development (up to years). Also, chronic inflammation is a non-specific promoter and weak initiator of the appropriate genetic changes of proto-oncogenes (necessary for normal growth and development of tissues) possibly through inflammatory oxygen free radical or nitric oxide/nitrite damage to DNA causing initiating mutations. The condition is rare and specifically results in sarcomas (specifically, fibrosarcomas). This specificity is unique for such a non-specific cause. This specificity could result from the site of injection chronic inflammation or something more hidden.
The fibrosarcomas are found in young cats more often than non-injection site fibrosarcomas (in cats mostly 11 years or older). The FISS are more aggressive and likely to fatally metastasize, and there seem to be predisposing factors. These characteristics suggest a viral association, although the common ones such as feline leukemia/lymphoma virus and the defective feline fibrosarcoma virus are not consistently present. The search for other viral causes or integrated components have not been exhaustively examined. Cats have endogenous retroviruses that can be expressed or defective integrated in the genomic DNA. An uncharacterized class of endogenous gammaretroviruses, termed ERV-DCs are present and hereditary in the domestic cat genome. Infectious gammaretrovirus is capable of infecting a broad range of cells from various species. Studies indicate that ERV-DC10 entered the genome of domestic cats in the recent past and appeared to translocate to or reintegrate at a distinct locus as infectious ERV-DC18. ERV-DC-like sequences were found in primate and rodent genomes, suggesting that these ERVs, and recombinant viruses such as RD-114 and BaEV (RD-114 is a feline ERV, while BaEV is a baboon ERV ) originated from an ancestor of ERV-DC. They found that a novel recombinant virus, feline leukemia virus subgroup D (FeLV-D), was generated by ERV-DC envelope gene transduction into feline leukemia virus in domestic cats. These results indicate that ERV-DCs behave as donors and/or acceptors in the generation of infectious, recombinant viruses. A precedent exists for defective viral recombination generating fibrosarcomas. Feline sarcoma virus (FeSV) is a type of retrovirus that causes tumors in cats, primarily fibrosarcomas (tumors of connective tissue). It’s a recombinant virus, meaning it’s formed by combining genetic material from Feline Leukemia Virus (FeLV) and the cat’s own cellular genes (specifically oncogenes). FeSV is replication-defective, requiring the presence of a helper FeLV to replicate.
Although vaccines or their adjuvants may be accused of causing cancer, at least in cats and much less so in dogs, they have a place in actually preventing cancer, such as for Feline Leukemia in cats and Marek’s Disease in chickens. Marek’s disease (MD) is a highly contagious viral disease in poultry, and vaccination is a key preventative measure. The Marek’s disease vaccine, typically a live virus, is administered to day-old chicks to help protect them from developing the disease and its associated tumors. Vaccinated birds can still become infected with MDV and potentially transmit it to unvaccinated birds, although the vaccine reduces the severity of the disease.
The final objection, beyond non-specific inflammatory reactions to vaccines, is allergic reaction to vaccines. This is wholly determined by the host. All vaccines have the potential to cause allergic, largely histamine mediated, acute reactions, swelling of the face, diarrhea, nausea, and hives (urticaria). However, any protein and some non-proteins can cause this, examples, peanut and penicillin, respectively. These on very rare occasions can be so severe that accidental aerosols from use in a confined area or drawing up the penicillin can cause even life threatening reactions. These are usually very rapid within 20 minutes up to 2 hours. Delayed reactions may arise from immune cellullsr responses,other than IgE and mast cell responses, which last longer than two hours to days. Allergic or hypersensitivity or autoimmune reactions to vaccines are usually the result of irrelevant antigens (those not responsible for the neutralization of the pathogens or prevention of disease) such as egg proteins in influenza vaccines because the viruses are grown in embryonated chicken eggs.
An autoimmune reaction often associated with vaccination is Guillain-Barré syndrome (GBS), an autoimmune disorder where the body’s immune system mistakenly attacks the peripheral nerves, leading to nerve damage and muscle weakness. However, the most common trigger for GBS is infection with Campylobacter jejuni, a bacterium that causes gastroenteritis, or infection of the digestive tract, the most common cause of food borne illness.
The first rabies vaccine was made from virus grown in rabbits and made from their spinal cords, leading to allergies and autoimmunity because of the presence of the rabbit neuronal proteins in the vaccine. This was replaced with vaccine produced in embryonated duck eggs with egg proteins on occasion causing allergic reactions, and finally from human cell cultured virus, which has the lowest probability of causing allergic reactions in humans. These irrelevant proteins may be introduced during the production of the vaccine.
When discovered, modern vaccine producers make every effort to remove these potentially allergenic materials. A classic example of this is in historical leptospirosis vaccines (more correctly called bacterins, killed pathogenic bacterial preparations) used in veterinary medicine. The media to grow leptospiras usually contains rabbit serum or bovine serum albumin that can trigger allergic reactions. Newer growth media or a protein extraction method are used in modern leptospirosis vaccines to reduce the potential for a reaction or make it no more frequent than with other canine vaccines. Rabbit serum provides essential nutrients and factors that support the growth of Leptospira, including native hemoglobin and other growth-promoting substances.
The concentration of rabbit serum in Leptospira media can vary between 3% and 10%.
Common media:
EMJH medium, a widely used medium for Leptospira, is often supplemented with rabbit serum.
Other media:
Other media, like Fletcher’s medium, also utilize rabbit serum for Leptospira cultivation.
Variations:
Some pathogenic strains may require specific supplements, like Ellis’s T80/40/LH medium, which includes polysorbate 40, lactalbumin hydrolysate, and superoxide dismutase along with rabbit serum.
Protein-Free Options:
Protein-free and low-protein media have also been developed, such as one based on charcoal-detoxified Tween and another supplemented with 0.1% bovine serum albumin.
Finally, in respect to COVID vaccines triggering autoimmunity compared to the infection itself:
Coronaviruses in general and SARS-CoV-2 in particular are associated with T17 pathway activation which plays a role in autoimmunity. I suspect repeated SARS-CoV-2 infections would more likely trigger autoimmunity (IgG4) than mere vaccination. Type T17 immunity is a specialized immune response crucial for defending against certain extracellular bacteria and fungi, particularly those that cause mucosal tissue damage, and intestinal parasites. It’s a distinct arm of the immune system, mediated by T helper 17 (Th17) cells and group 3 innate lymphoid cells (ILC3s), and characterized by the production of the cytokine IL-17A. This type of immunity is important for maintaining mucosal homeostasis and can be involved in both protective and inflammatory responses. Dysregulation of type 17 responses can contribute to chronic inflammatory disorders, such as inflammatory bowel disease (IBD) and other autoimmune diseases.
All modern vaccine producers have carefully considered all these potential problems, and the best of biomedical science has worked hard to reduce them to insignificance so vaccines can continue to save millions of lives from suffering and death.
Selected References
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Kinney RM, Chang GJ, Tsuchiya KR, Sneider JM, Roehrig JT, Woodward TM, Trent DW. Attenuation of Venezuelan equine encephalitis virus strain TC-83 is encoded by the 5′-noncoding region and the E2 envelope glycoprotein. J Virol. 1993 Mar;67(3):1269-77. doi: 10.1128/JVI.67.3.1269-1277.1993. PMID: 7679745; PMCID: PMC237493.
Woodward KN. Origins of injection-site sarcomas in cats: the possible role of chronic inflammation-a review. ISRN Vet Sci. 2011 Apr 12;2011:210982. doi: 10.5402/2011/210982. PMID: 23738095; PMCID: PMC3658838.
Zajc AL, Harper A, Benoit J, Mason S. Non-injection-site soft tissue sarcoma in cats: outcome following adjuvant radiotherapy. J Feline Med Surg. 2022 Aug;24(8):e183-e193. doi: 10.1177/1098612X221098961. Epub 2022 May 31. PMID: 35639367; PMCID: PMC10812266.
Anai Y, Ochi H, Watanabe S, Nakagawa S, Kawamura M, Gojobori T, Nishigaki K. Infectious endogenous retroviruses in cats and emergence of recombinant viruses. J Virol. 2012 Aug;86(16):8634-44. doi: 10.1128/JVI.00280-12. Epub 2012 Jun 6. PMID: 22674983; PMCID: PMC3421742.
Esau D. Viral Causes of Lymphoma: The History of Epstein-Barr Virus and Human T-Lymphotropic Virus 1. Virology (Auckl). 2017 Sep 25;8:1178122X17731772. doi: 10.1177/1178122X17731772. PMID: 28983187; PMCID: PMC5621661.
Leonard RA, Spurrier MA, Skavicus S, Luo Z, Heaton BE, Spreng RL, Hong J, Yuan F, Heaton NS. Development of DNA and mRNA-LNP vaccines against an H5N1 clade 2.3.4.4b influenza virus. J Virol. 2025 Jul 16:e0079525. doi: 10.1128/jvi.00795-25. Epub ahead of print. PMID: 40667976.
















































































































