A look into the development of vaccines and the scientists who invented them
Written by Shriya
Vaccines have saved millions of lives worldwide and dramatically reduce the prevalence of many life threatening infectious diseases. Unlike most medicines that treat or cure diseases, vaccines prevent a person from getting sick with the disease in the first place. In this way, they can give a person immunity from getting the disease. Vaccines cause a small amount of a weakened or killed virus, bacteria, or protein that imitates the virus in order to prevent infection by the same virus or bacteria. (1) Immunization currently prevents 2-3 million deaths every year from diseases like diphtheria, tetanus, pertussis, influenza and measles.
A Brief History:
Before we explore more about vaccines, it is important to understand how they were developed.
The practice of immunization dates back hundreds of years. Buddhist monks drank snake venom to confer immunity to snake bite and variolation was practiced in 17th century China. (2)
Edward Jenner is considered the founder of vaccinology in the West. The basis of
vaccinations began when Dr. Jenner observed that milkmaids who had previously gotten cowpox did not show any symptoms of smallpox after variolation. (3) The first experiment to test this theory involved milkmaid Sarah Nelmes and James Phipps, the 9 year-old son of Jenner’s gardener. Dr. Jenner took material from a cowpox sore on Nelmes’ hand and inoculated it into Phipps’ arm. Months later, Jenner exposed Phipps a number of times to the virus, but Phipps never developed smallpox. In doing so, it was shown that Phipps had developed an immunity to smallpox. Based on these findings, Jenner developed the first smallpox vaccine in 1798. Jenner’s method underwent medical and technological changes over the next 200 years and eventually resulted in the eradication of smallpox. (4)
Louis Pasteur’s vaccine was the next to make an impact on human disease. Influenced by Edward Jenner, Pasteur reasoned that if a vaccine could be found for smallpox, vaccines could be also found for other diseases. In 1879, Pasteur observed that old bacterial cultures
lost their virulence. He had instructed an assistant to inject chickens with a fresh culture of the viral bacteria. (5) However, the assistant forgot to do so. When he returned some time later, the assistant performed the procedure using the old culture. The chickens only showed mild signs of the disease and survived. When they were healthy again, Pasteur injected them with fresh bacteria. Since the chickens did not become ill, Pasteur reasoned the factor that made the bacteria less deadly was exposure to oxygen. The microbe, weakened in the lab, had taught the chicken immune system to fight the infection without causing any serious harm to the chicken. This type of vaccine is called a live, attenuated vaccine. By applying this technique, in 1881, he helped develop a vaccine for anthrax, which was used successfully in sheep, goats and cows. Then, in 1885, while studying rabies, Pasteur tested his first human vaccine. Pasteur produced the vaccine by attenuating the virus in rabbits and subsequently harvesting it from their spinal cords. Through his discoveries, Pasteur revolutionized work in infectious diseases and his work can be considered the birth of immunology. (5)
Waldemar Haffkine stressed the importance of the discovery of inoculating with microorganisms of an increased and fixed state of virulence obtained by passage through animals. After many false starts, Haffkine discovered that by repeated passages of Asiatic cholera bacilli through the peritoneal cavity of guinea pigs, he could obtain a culture of bacilli with an increased virulence. An attenuated culture was produced by exposing the fixed culture to raised temperature conditions. These findings confirmed the efficacy of the inoculation. Haffkine then used this knowledge to develop the anti cholera vaccine. Experience gained from testing the anti cholera vaccine was used to try and evaluate the effectiveness of the anti plague vaccine. (6)
The developments in vaccines proved especially important in combating the polio epidemic. In the U.S. in 1916, more than 27,000 people were paralyzed by the disease and at least 6,000
people died from it. For the next several decades, the epidemic expanded throughout the U.S. and Europe. In 1952 alone, there were 58,000 new cases of polio and 3,000 deaths from the disease in the U.S. (7) Researchers began working on a polio vaccine in the 1930s. However an effective vaccine didn't come around until 1953, when Jonas Salk introduced his inactivated polio vaccine. Salk was able to grow poliovirus in monkey kidney cells. He then isolated the virus and inactivated it with formalin, which is an organic solution of formaldehyde and water. Salk's vaccine was unique because instead of using a weakened version of the live virus, it used a "killed," or inactivated, version of the virus. (6) When this version of poliovirus is injected into the bloodstream, it is unable to cause an infection since the virus is inactive. However, the immune system can't distinguish an activated virus from an inactivated one, so it still creates antibodies to fight the virus. Those antibodies persist and protect the person from poliovirus infection in the future.
While Salk was developing his inactivated polio vaccine, Dr. Albert Sabin was working on a
vaccine made with an active, weakened virus. Sabin opposed Salk's vaccine design and considered an inactivated virus vaccine to be dangerous. By 1963, Sabin had created an oral live-virus vaccine for all three types of poliovirus. This version was cheaper and easier to produce than the Salk vaccine, and it quickly supplanted the Salk vaccine in the U.S. in 1972. (7) Sabin's oral polio vaccine was critical for helping to decrease the number of polio cases globally. However, unlike the Salk vaccine, Sabin’s vaccine did carry an extremely small risk of causing paralysis.
Throughout history, vaccines have been developed and improved to address a wide number of diseases. The past two decades have seen the application of molecular genetics in immunology, microbiology and genomics applied to vaccinology. Molecular genetics sets the scene for a bright future for vaccinology, including the development of new vaccine delivery systems. Innovative techniques now drive vaccine research, with recombinant DNA technology and new delivery techniques leading scientists in new directions. Disease targets have expanded, and some vaccine research is beginning to focus on non-infectious conditions such as addiction and allergies. (4) Various diseases that once led to death are now seen as rare and preventable. As we continue making strides in research, vaccinations have proven to be truly life-changing.
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