Trevor James
Jonas Salk developed one of the first successful polio vaccines, which was announced in 1955. The vaccine was based on three wild, virulent reference strains, Mahoney (type 1 poliovirus), MEF-1 (type 2 poliovirus), and Saukett (type 3 poliovirus), grown in a type of monkey kidney tissue culture (Vero cell line). However, it was later discovered that the monkey kidney cells used in the development of the Salk and Sabin polio vaccines contained a cancer-causing monkey virus called SV40. Koprowski, a polio researcher, also worked on a version of the polio vaccine grown in fetal cells, but this approach was not agreed upon by all scientists.
| Characteristics | Values |
|---|---|
| Fetal cells used in the development of vaccines for | Polio, rubella, chickenpox, shingles, hepatitis A, and rabies |
| Fetal cell researcher | Leonard Hayflick |
| Scientist who successfully grew the poliovirus in cell culture | Frederick Robbins, Thomas Weller, and John Enders |
| Year the poliovirus was successfully grown in cell culture | 1949 |
| Creator of the Salk vaccine | Jonas Salk |
| Year the Salk vaccine was created | 1953 |
| Year the Salk vaccine was announced as safe | 1955 |
| Year the Salk vaccine reached about 90 countries | 1959 |
| Creator of the oral polio vaccine | Albert Sabin |
| Year the oral polio vaccine came into commercial use | 1961 |
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What You'll Learn
The development of the Salk polio vaccine
Polio is a highly infectious disease that primarily affects young children, attacking the nervous system and leading to potential paralysis and even death. The development of the Salk polio vaccine was a groundbreaking achievement in the history of medicine, significantly reducing the number of poliomyelitis cases worldwide. The story of its development began in the early 20th century and involved the contributions of numerous scientists and researchers.
In 1908, Landsteiner and Popper conducted a study using porcelain size exclusion filters, demonstrating that polio paralysis was caused by something smaller than a bacterium. This led to the conclusion that a virus was responsible for polio, setting the goal of developing a vaccine. Several decades later, in 1949, Bodian, Morgan, and Howe classified three different types of poliovirus (Types I, II, and III) based on the immunologic responses of monkeys to various polio strains. This discovery was crucial as it indicated that a maximally effective poliovirus vaccine would need to be trivalent, containing inactivated viruses from each of the three distinct viral groups.
That same year, John Enders, Thomas Weller, and Frederick Robbins successfully cultivated poliovirus in human tissue at Boston Children's Hospital. Their method did not require human embryonic brain tissue, addressing health concerns associated with previous culturing techniques. Enders, Weller, and Robbins received the 1954 Nobel Prize in Physiology or Medicine for their groundbreaking discovery, paving the way for vaccine development.
In 1953, Hammon's research demonstrated the protective effects of antipolio immunoglobulin against paralytic polio in epidemic areas. This provided further evidence that generating an antipolio antibody response could be an effective strategy for preventing paralytic polio. Following these scientific breakthroughs, Jonas Salk, a US physician, began working on a poliovirus vaccine at the University of Pittsburgh.
Salk's commitment to equitable access to his vaccine was evident as he did not profit from sharing the formulation or production processes. He believed that the vaccine belonged to the people, famously stating in a 1955 interview, "There is no patent. Could you patent the sun?" Salk's inactivated polio vaccine (IPV) was licensed on April 12, 1955, after successful trials and testing. The results showed a significant drop in polio cases, and by 1961, only 161 cases remained.
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Fetal cells in vaccine production
The use of fetal cells in vaccine production is a highly debated topic, with various moral, ethical, and religious implications. While some people find the use of fetal cells from abortions morally reprehensible, others believe it is completely justified for scientific research and vaccine development.
The history of fetal cell use in vaccines goes back to the 1940s and 1950s when scientists like John Enders, Thomas Weller, and Frederick Robbins successfully cultivated the poliovirus in human tissue and cell culture. This breakthrough led to the development of the first polio vaccines by Jonas Salk and Albert Sabin in the early 1950s. However, it was later discovered that the monkey kidney cells used to grow the Salk and Sabin polio vaccines contained a cancer-causing virus called Simian Virus-40 (SV40).
Following the success of the initial polio vaccines, researchers explored the use of fetal cells in creating vaccines for other diseases. Leonard Hayflick, a scientist at the Wistar Institute, focused on creating continuous cell lines from fetal tissue. The WI-38 cell line, derived from a single abortion, was shared with researchers worldwide and used to develop vaccines against polio, rubella, and rabies. This cell line was also used in public health labs and sent to World Health Organization (WHO) labs on four continents for disease detection.
The use of fetal cells in vaccine production has continued, with vaccines for rubella, chickenpox, shingles, hepatitis A, and rabies being made using these cells. However, the use of fetal cells has sparked controversy, with some scientists and organizations expressing concerns about undetected viruses and the need for better characterization of the cells. Additionally, religious beliefs opposing abortion and the use of aborted fetal tissue for research or medical purposes have also been raised as objections to the use of fetal cells in vaccines.
While the use of fetal cells in vaccine production has been a subject of debate, it is important to note that fetal cells are not present in the final vaccine product. Instead, their macromolecular proteins and growth factors are utilized to facilitate the rapid proliferation of the desired cells. Strict guidelines and quality control measures are implemented by global government agencies to ensure the safety and integrity of vaccine manufacturing processes.
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Monkey kidney cells and the SV40 virus
Jonas Salk's inactivated polio vaccine (IPV), developed in the early 1950s, was a major breakthrough in the fight against polio. However, it was later discovered that the monkey kidney cells used to grow the Salk and Sabin polio vaccines contained a cancer-causing virus called Simian Virus-40 (SV40). This virus was present in the polio vaccine administered from 1955 to 1963, exposing 98 million Americans and countless others worldwide to the contaminated vaccine.
SV40 is a monkey virus that can cause cancers in animals. It induces transformation in primary cultures of monkey kidney cells, leading to the formation of complement-fixing viral antigens and increased resistance to the cytopathic effects of the virus. The presence of SV40 in the polio vaccine raised concerns about its potential impact on humans, as it has biological properties consistent with cancer-causing viruses.
While studies have been conducted to assess the risk of cancer development in those who received the contaminated vaccine, the results are inconclusive. Some studies have found SV40 in human mesotheliomas, brain and bone cancers, lymphomas, and other cancers. However, other studies have shown no increased cancer risk in those who received the contaminated vaccine. The Institute of Medicine's Immunization Safety Review Committee concluded that the evidence was inadequate to determine a definitive link between the contaminated polio vaccine and cancer risk.
In response to the contamination, steps were taken to eliminate SV40 from future vaccines. The vaccine was replaced with Aventis Pasteur's killed polio vaccine grown on a well-characterized VERO monkey cell line, reducing the likelihood of further contamination by unrecognized viruses. This incident highlights the importance of thorough virus detection and characterization in vaccine development to ensure the safety and effectiveness of vaccines for public health.
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Jonas Salk's work at the University of Pittsburgh
Jonas Salk was an American virologist and medical researcher who developed one of the first successful polio vaccines. He was born in New York City and attended the City College of New York and New York University School of Medicine. In 1947, Salk accepted a position at the University of Pittsburgh School of Medicine, where he began a project to determine the number of different types of poliovirus.
At the University of Pittsburgh, Salk devoted himself to developing a vaccine against polio. He collaborated with scientists from other universities to classify the various strains of poliovirus and identified three separate strains. He then demonstrated that a killed virus of each of the three strains, while unable to cause the disease, could induce antibody formation in monkeys. In 1952, he conducted successful field tests of his killed-virus vaccine on children who had recovered from polio and those who had not previously had the disease.
Salk's vaccine was first tested on himself and his family in 1953, and later on 1.6 million children in Canada, Finland, and the USA in 1954. The results were announced on April 12, 1955, and Salk's inactivated polio vaccine (IPV) was licensed the same day. Salk chose not to patent the vaccine or profit from it, instead focusing on maximizing its global distribution.
The University of Pittsburgh, along with the National Foundation for Infantile Paralysis, considered patenting the vaccine. However, their efforts were hindered as Salk's techniques were not considered novel. Salk's work at the University of Pittsburgh led to a significant reduction in polio cases, with annual cases dropping from 58,000 to 5,600 by 1957.
Salk's contributions to the field of medicine were recognized through numerous honours, including the Presidential Medal of Freedom awarded in 1977. The Municipal Hospital building at the University of Pittsburgh, where Salk conducted his polio research, was renamed Jonas Salk Hall in 1957.
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The global impact of the Salk vaccine
Jonas Salk created the first successful polio vaccine in the early 1950s. Unlike other vaccine developers of the time, Salk's vaccine was based on killed poliovirus, making it safer and simpler to produce. After testing his experimental vaccine on himself and his family in 1953, Salk's vaccine underwent rigorous testing in one of the largest clinical trials in history, with nearly 2 million children participating.
On April 12, 1955, it was announced that the vaccine was safe and effective, and Salk's inactivated polio vaccine (IPV) was licensed. This led to an unprecedented drop in polio cases. By 1957, annual cases in the US dropped from 45,000 to 5,600, and by 1961, only 161 cases remained. Worldwide, polio cases have fallen by more than 99% since the introduction of the Salk vaccine, thanks to expanded immunization programs and collaborative global efforts.
Salk's commitment to equitable access to his vaccine was demonstrated by his refusal to patent it, ensuring its widespread distribution. Six pharmaceutical companies were licensed to produce IPV, and Salk did not profit from sharing the formulation or production processes. This decision played a crucial role in the global impact of the vaccine.
The Salk vaccine's impact has been long-lasting. By 1994, polio had been eliminated from the Americas, and by 2000, the Western Pacific region was polio-free. As of 2020, the World Health Organization's (WHO) African region was certified polio-free, and the Eastern Mediterranean region has restricted the virus to a handful of districts. The ongoing efforts to completely eradicate polio remind us of the importance of global vaccination initiatives in safeguarding humanity.
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Frequently asked questions
No, Jonas Salk did not use fetal cells in his polio vaccine. The vaccine was based on three wild, virulent reference strains, Mahoney (type 1 poliovirus), MEF-1 (type 2 poliovirus), and Saukett (type 3 poliovirus), grown in a type of monkey kidney tissue culture (Vero cell line).
Salk created an inactivated (killed) polio vaccine (IPV), which was injected. This was different from the oral polio vaccine (OPV) developed by Albert Sabin, which came into commercial use in 1961.
Salk believed that an inactivated vaccine would be safer than using weakened forms of the poliovirus. He decided to use what he called a killed-virus vaccine, which he tested on himself and his family in 1953.
No, Salk did not patent the vaccine or seek any profit from it. Instead, he wanted to maximize its global distribution.
