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It is hard to fully appreciate how vaccines have revolutionized modern medicine. The long schedule of vaccines may seem like a hassle, and rumors about harmful effects unnerve parents. But, the fact is, vaccines have helped save millions and millions of lives. Just a few generations ago, people lived under the constant threat of deadly infectious diseases, like smallpox, polio, and hepatitis.
Let's look at the greatest infectious scourges of the past 1,000 years and how vaccines have mitigated or even eradicated the danger.
Prior to the 15th Century: Infectious disease has always impacted humanity, but even as early as 1,000 years ago, there is evidence people recognized the connection between exposure and immunity. The ancient Chinese may have used pulverized smallpox scabs taken from the sick and inhaled or rubbed them onto skin to immunize themselves. This primitive form of inoculation was practiced in Africa and the Middle East too before spreading to Europe.
16th Century: Smallpox, measles, and whooping cough were terribly common in the 1500s, with outbreaks recorded around the world. Contagious diseases like these spread quickly, especially in crowded, dirty cities. Children were especially vulnerable. Records from 16th century England indicate that as many as 30% of all children died before the age of 15, likely from dysentery, scarlet fever, whooping cough, influenza, smallpox, and pneumonia.
17th Century: When Christopher Columbus discovered the Americas in 1492, he and the Europeans that followed him unwittingly brought with them smallpox, measles, whooping cough, chicken pox, bubonic plague, typhus, and malaria. The native people, with no history of these diseases and no natural resistance, died by the millions over the 150 years that followed initial contact with European explorers. An estimated 80% to 95% of the population perished. There is perhaps no more terrible an example from history to illustrate the importance of antibodies in resisting infectious disease.
18th Century: The 1700s were a watershed century for vaccine development. Europeans realized that survivors of certain infectious diseases were immune to future exposure, and began a primitive form of inoculation by intentionally infecting themselves with a disease to gain immunity.
The risk of sickness and death with this early approach was high, but it shed light on the basic principles behind immunology and enabled British doctor Edward Jenner to develop the world's first true vaccine. In 1796, Jenner discovered that if he infected people with the related, though relatively benign, cowpox virus he could inoculate patients with far lower mortality rates.
19th Century: After Dr. Jenner's discovery of "cow pox" as the first relatively safe vaccination against smallpox, knowledge of the procedure spread rapidly and became common throughout the world. Vaccine development finally made another major step forward 85 years later when Louis Pasteur identified bacteria as a major culprit behind several diseases and used this knowledge to produce the first "lab-made" vaccination.
20th Century: At the start of the 20th century, infectious diseases like yellow fever and polio still ravaged populations in Europe and the United States. But as the century progressed, scientists built upon the immunological fundamentals discovered over the past century and developed individual vaccinations for 27 major infectious diseases. By the year 2000, centuries-old scourges like smallpox and measles were virtually eliminated from the developed world, along with yellow fever, polio and several others.
21st Century: Since 1995, five new vaccines were added to the children's immunization schedule in the U.S., which the CDC estimated saved thousands of lives. The pneumococcal conjugate vaccine, added in 2001, likely saved 13,000 U.S. lives from 2001 to 2008. And the rotavirus vaccination, added in 2006, is now estimated to prevent 40,000 – 60,000 hospitalizations yearly.
On the global scale, health organizations continue to distribute vaccines to poorer countries. Thanks to increased access to the measles vaccine internationally, the annual death toll from the disease has fallen from almost 600,000 in 2000 to just 122,000 in 2012, a reduction of 79%.
Future of Vaccines: While existing vaccines continue to be improved and distributed, the scientific community continues to work on a few difficult diseases. There is no working vaccine for HIV, malaria, or tuberculosis (there is a TB vaccine for children, but not adults). Consequently, these diseases continue to kill millions around the world.
A new generation of cancer vaccines, designed to train the body to better fight cancer, is also in early stages of development. The scientific community believes these drugs hold great promise for addressing growing rates of cancer, now the second most common cause of death in the United States.