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Vaccine Success Has Long History

In September 2008, a group of researchers at the University of Pennsylvania modified messenger RNA (mRNA) in a way that stabilized the molecule and made mRNA a promising tool for both gene replacement and vaccination. This relatively new technology was used in 2020 to rapidly develop and manufacture a COVID-19 vaccine. This represents the latest in a series of breakthroughs in the realm of viral vaccines, each building on the last and each with a compelling record of disease prevention.

The first major vaccine-related advance occurred in 1796 when Edward Jenner, a physician who had a laboratory in southern England, found that an animal virus (cowpox) could protect against a human virus (smallpox), although it would be over 100 years before viruses were discovered as causative agents of disease. Jenner’s work ultimately led to the elimination of a disease that is estimated to have killed over 300 million people in the 20th century. That strategy of using animal viruses to prevent human disease continues today.

The second vaccine breakthrough occurred almost 100 years later, in 1885. Louis Pasteur found that the spinal cords of rabbits that had been experimentally injected with rabies virus were no longer infectious after 15 days of desiccation (drying). On July 6, 1885, Joseph Meister, a 9-year-old boy who had been attacked by a rabid dog, was taken to Dr. Pasteur’s lab. Using a series of inoculations with suspensions of desiccated rabbit spinal cords, Pasteur saved Meister’s life. Rabies, a disease with a mortality rate of nearly 100%, was now preventable after exposure.

Pasteur opened the door for vaccines made with physically or chemically inactivated viruses. During the 20th century, vaccines using this killed-virus strategy included an influenza virus developed by Thomas Francis in the early 1940s, a polio vaccine developed by Jonas Salk in the mid-1950s (Salk had trained at Francis’ laboratory at the University of Michigan), and a hepatitis A vaccine that was developed in 1991.

The third major advance occurred in 1937 when Max Theiler attenuated (weakened) the yellow fever virus by serial passage through mouse and chicken embryos. This rendered the virus less capable of causing disease but still capable of inducing protective immunity in humans. He won the 1951 Nobel Prize in Medicine for that work. Other attenuated virus vaccines followed including measles, mumps, rubella, varicella, and rotavirus. The next breakthrough came in 1980 when biochemists at Stanford University published their work that used Escherichia coli genes that were passed through monkey kidney cells, causing those cells to make a bacterial protein (antibodies). This recombinant DNA technology allowed for the creation of vaccines for hepatitis B, human papillomavirus, and influenza.

Despite the fact that there is still much work to be done to address vaccine hesitancy, build trust, and ensure equitable benefits from vaccination, the list of vaccine successes is long. For example, after the introduction of Salk’s polio vaccine, the number of polio cases in the U.S. dropped from 29,000 in 1955 to 900 in 1962, and the disease is now eliminated here. During the 2019-2020 flu season, flu vaccines prevented an estimated 7.52 million infections, 3.69 million medical visits, 105,000 hospitalizations, and 6,300 deaths in the U.S. And now, with the worst pandemic since 1918, when influenza killed about 50 million people worldwide, we are again seeing vaccines become an important strategy in ridding the world of SARS-CoV-2, especially the Pfizer and Moderna vaccines that use the new mRNA technology which, as they don’t contain the actual virus, cannot cause even a mild case of case of COVID-19.

Questions and comments may be sent to editor@rockawaytimes.com.

 By Peter Galvin, MD

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