The Remarkable Journey from Desiccated Scabs to Genomic Vaccines

Anthony L. Esposito, MD George M. Abraham, MD

The practice of immunization against communicable diseases is centuries old. Evidence exists that by 1000 BCE, Chinese practitioners were immunizing against smallpox by grinding up desiccated smallpox scabs and blowing the material through long, silver tubes into the noses of children. Immunization may also have been achieved in Asia by scratching material from a lesion of a patient with a mild case of smallpox into the skin of a susceptible person, a practice referred to as variolation. Not surprisingly, the use of such crude preparations resulted not only in protection against severe smallpox but also in the transmission of both mild and serious infections. Variolation was also practiced in Turkey and Africa before arriving in Europe and the Americas.

Vaccine development in the west began in 1796 when Edward Jenner, a country physician, inoculated an eight-year-old boy with pus taken from a cowpox lesion on a milkmaid’s hand. A few weeks later, Jenner inoculated two sites on the boy’s arm with variolous material, either desiccated smallpox scabs or fluid from pustules. The boy remained well after that challenge as well as after a second. On the basis of 12 such experiments and other clinical cases, Jenner published a report, “Inquiry Into the Causes and Effects of the Variolae Vaccine,” in which he concluded, “the cowpox protects the human constitution from the infection of smallpox.”

It was common knowledge milkmaids were unaffected by smallpox, a disease which killed 10 to 20% of the population in towns and cities. It is also of note that others in England and Europe had immunized subjects with material containing the cowpox virus. However, Jenner was the first to expose cowpox-vaccinated subjects to smallpox and to prove vaccination protected against the disease. Jenner’s investigations, and his efforts to disseminate what he learned, led to the eventual eradication of smallpox in 1979. It is not an understatement to say that Jenner’s work and the subsequent investigations it spawned have saved more lives than any other medical intervention in human history.

Programs designed to vaccinate large populations against smallpox in the 1800s were met with criticisms and resistance based on religious, scientific and political grounds. Some of the objections were easy to understand. For example, the concept of scoring a child’s arm and exposing the open wound to infectious material from another human would have been daunting in any era. Other objections were anchored in religious beliefs (i.e., the vaccine were “unchristian”), scientific skepticism (i.e., show me the data), and common knowledge of the era (i.e., smallpox was due to putrid humors in the air). In addition, others of the period resisted because of a general distrust in medicine or because vaccinations violated their personal rights. As governments, including those in the United States, created laws known as Vaccination Acts requiring vaccination and, in some cases, included penalties for non-compliance, resistance hardened as citizens demanded the right to control their and their children’s bodies. In England, the Vaccination Act spawned the London Society for the Abolition of Compulsory Vaccination and the Anti-Compulsory Vaccination League, which campaigned against “The Vaccination Humbug” and which became the National Anti-Vaccination League. Political theater of the time included the Leicester Demonstration March of 1885 in which 80,000 to 100,000 anti-vaccinators marched with banners, a child’s coffin, and an effigy of Jenner.

Resistance to mandatory vaccination spread to the United States and, in 1882, the New England Anti-Compulsory Vaccination League was formed followed in 1885, by the Anti-Vaccination League of New York City. Using pamphlets, court battles and fights on the floors of state legislatures, the anti-vaccinationists succeeded in repealing compulsory vaccination laws in several states. The struggle between anti-vaccinationists and public health officials was protracted in the courts and beyond. Anti-vaccinationists were responsible in 1894 for instigating riots in Milwaukee which included the stoning of ambulances and public health workers.

Beyond the political arena, the 1880s and 1890s were periods of explosive microbial discovery when many of the bacteria causing human diseases were first isolated. These diseases included anthrax, first isolated by Robert Koch; cholera (Filippo Pacini and Robert Koch); diptheria (Edwin Klebs and Friedrich Löffler); tetanus (Arthur Nicolaier); and tuberculosis (Koch). Other bacteria isolated from ill humans with respiratory tract infections during the period included hemophilus (Richard Pfeiffer) and pneumococcus (Louis Pasteur).

The identification of bacteria responsible for common infections coupled with the success of Jenner’s vaccine in controlling smallpox across the globe spurred subsequent efforts to develop vaccines against a range of human maladies. Examples of early successes include the work of Jaime Ferran who, in 1885 developed a live, attenuated cholera vaccine that, when administered into soft tissues of the arm was partially effective against the disease. Also of note are the studies of Shibasaburo Kitasato and Emil von Behring who demonstrated serum derived from immunizing laboratory animals with heat-treated diphtheria toxin could cure other laboratory animals and, in 1892, proved these same positive results when given to humans with diphtheria.

The most successful vaccine of the era was Pasteur’s against rabies, an invariably fatal infection. Studies done in 1804 demonstrated saliva from a rabid dog could transmit the disease to a non-infected one and to other animals. Later investigations showed animals injected intravenously with saliva from a rabid animal would not develop the disease. Pasteur extended this work and showed the virulence of the microbe which was causing rabies became progressively attenuated when passed from a dog to a monkey and then from monkey to monkey. On the other hand, virulence could be increased when passed from rabbit to rabbit or guinea pig to guinea pig. He showed the exposure of neural tissues from a rabid animal to dry air also produced an attenuation in virulence. In 1885 using emulsions of spinal cords from rabid rabbits that had been kept in dry air for varying times, he “treated” successfully, i.e., administer a 9-year-old boy bitten by a rabid dog, thus demonstrating the efficacy of post-exposure prophylaxis. In 1886, Pasteur reported he had similarly treated 350 patients with only one fatality.

Pasteur’s contributions included discovering methods to attenuate the virulence of animal pathogens leading to vaccines that prevented outbreaks which decimated flocks and herds. He demonstrated sheep and other domesticated animals could be successfully vaccinated with an anthrax bacillus exposed to high temperatures or carbolic acid and that chickens could be protected from fowl cholera by inoculation with old cultures of the bacterium that caused the disease. Unaware of the impact of genetic changes on a microbe’s virulence, he attributed attenuation to a depletion of some element crucial to growth. Pasteur’s demonstration that microbial attenuation could lead to useful vaccines became a mainstay in the subsequent development of human vaccines. By the end of the 19th and early 20th centuries, attenuated, whole cell vaccines had been developed against typhoid, plague and other bacterial diseases.

The 20th century process of vaccine development followed the paths established in the late 19th century: isolate or identify the offending microbe, identify potential virulence factors (i.e., exotoxins or capsular polysaccharides), and develop vaccines based on the administration of an attenuated microbe, the microbe’s exotoxin (e.g., inactivated diphtheria toxin or diphtheria toxoid), or a virulence factor potentially linked to a carrier molecule (e.g., protein conjugated pneumococcal, meningococcal or Hemophilus influenzae capsular polysaccharides). The development of a potential vaccine would be accompanied by trials to confirm safety and an adequate immune response followed by clinical trials to confirm efficacy or protection.

Unavailable to researchers in the 19th century, 20th-century vaccine researchers had tools to quantitate the humoral and cellular immune response to bacterial and viral antigens and to assess the effectiveness of that response in in vitro tissue cultures and in vivo animal models prior to introducing a vaccine into humans where measures of immune response, such as antibody titers, could be correlated with vaccine efficacy.

The value of the traditional process of vaccine development and introduction is highlighted by the impact vaccines had during the 20th century. The Centers for Disease Control and the National Institute of Allergy and Infectious Diseases report that prior to the introduction of effective vaccines and immunization programs, 500,000 cases of measles, 175,000 cases of diphtheria, 47,000 cases of rubella and 16,000 cases of polio occurred each year in the United States. What has been the impact of effective vaccines? In 2019, there were 1,282 cases of measles, a record high for the decade; two cases of diphtheria; and less than 10 cases of rubella reported in the United States. Polio, like smallpox, has been eradicated and a bacterium; Haemophilus influenza, type B, which only decades ago caused 20,000 infections annually and 1,000 deaths in infants and children; has largely become a disease of historical interest.

Vaccine development is a long process and 10 to 15 years are often required to move a potential vaccine through the customary stages of exploration; preclinical laboratory studies; Phase I, II and III clinical trials; and finally review and approval by the U.S. Food and Drug Administration. In addition, the use of attenuated, whole microbes as antigens suffers from the limitation that the vaccinated host may respond to multiple antigens not relevant to protective immunity. Past pandemics have shown that vaccine development and introduction during outbreaks were not fast enough to have an impact on the disease at hand, even when the technology to produce the vaccine was available (e.g., H1N1 influenza pandemic of 2009). Indeed, recent Ebola and Zika epidemics ended before vaccines under development became available.

As we have witnessed with the current COVID-19 pandemic, the evolution of molecular biology and genetic engineering has changed the landscape of vaccine development. In early genetic vaccine development, bacteria, yeast or other cells were given the genetic sequences necessary to produce a desired antigen such as the hepatitis B surface antigen. Although the engineered cells may be able to produce substantial quantities of the antigen, the amount needed might not be met by the process. In particular, the failure to expeditiously produce a vaccine during the 2009 H1N1 pandemic led to a search for novel development and production platforms.

We have witnessed one such novel platform in action. Within weeks following the release of the gene sequences of SARS-CoV-2, the cause of COVID-19, scientists had identified the genetic segment responsible for encoding the virus’ primary virulence factor, the spike glycoprotein. In turn, the molecular structure and chemical composition of the spike glycoprotein were quickly elucidated. Using an entirely synthetic processes, Moderna and Pfizer–BioNTech each created a vaccine that consisted of the mRNA sequence encoding a portion of spike protein; the receptor binding domain, or RBD; and a lipid envelope. In March 2020, within three months of the publication of the virus’ genome, Phase I clinical trials were underway. Phase II and III trials quickly followed and, on Dec. 11, 2020, the Pfizer BioNTech vaccine was released under an emergency use authorization. The Moderna vaccine received the same clearance the following week.

The platforms for synthesizing mRNA vaccines created an enormous number of doses. By the end of August 2021, approximately 350 million doses of the two mRNA vaccines had been administered to residents of the United States. Epidemiologists have estimated the two vaccines, which had demonstrated efficacies of greater than 90% in persons of all ages in reducing the risk of hospitalization and death, have saved tens of thousands of hospitalizations and lives.

The stunning introduction and efficacy of the mRNA vaccines have not been without controversy due to misinformation, especially regarding a belief that the vaccine can alter a recipient’s DNA. In fact, the mRNA injected into the muscle cells of the upper arm promptly instructs the cells to produce the RBD of the spike protein, but it does not enter the cell’s nucleus or comingle with the host’s DNA. Indeed, being a fragile molecule, the mRNA disintegrates about 72 hours after entering muscle cells. The spike RBD protein produced in response to the mRNA is seen as foreign and as such elicits a cellular and humoral immune response, the latter including the production of neutralizing antibodies. These antibodies bind to the spike’s RBD, which is responsible for attaching to host-cell receptors; the angiotensin converting enzyme, or ACE2; and initiating host-cell invasion. Thus, neutralized by antibodies, SARS-CoV-2 cannot infect targeted cells and the recipient’s DNA remains intact and unaltered.

Given the impact of global warming, the extent of human intrusion on ecosystems and the scope of international travel, the likelihood of another coronavirus or other viral pandemic appears almost certain. One reassuring lesson from the current crisis is that the scientific ability to swiftly characterize novel microbes to the atomic level is remarkable and without precedent. Similarly, the ability of dedicated researchers to elucidate interactions between microbe and host at the molecular level is equally breathtaking. Finally, the ability of governments and private industry to work together to produce and distribute life-saving vaccines is equally impressive. In short, medical science has come a long way from using desiccated scabs to inoculate susceptible populations. However, it is worth remembering, “antivaxxers” agitating in 2021 were preceded by those in the 1800s who found the smallpox vaccine unacceptable and who resisted its introduction. So, while mRNA vaccines should be considered game changers in medicine, human nature appears sadly unyielding in its adherence to irrational, narcissistic and self-destructive impulses.

Anthony L. Esposito, MD Hospital Epidemiologist, Saint Vincent Hospital Professor of Medicine University of Massachusetts School of Medicine

George Abraham, MD Chief of Medicine, Saint Vincent Hospital Professor of Medicine University of Massachusetts School of Medicine