Of all the scientific breakthroughs that have transformed humanity, the development of vaccines is undoubtedly among the most important in terms of human survival. Diphtheria, polio, rubella and whooping cough are just a few of the diseases that can be prevented with vaccines [source: History of Vaccines]. In fact, some diseases have been completely eradicated through the use of vaccines. One example is smallpox, which once killed 35 percent of its victims [source: History of Vaccines].
In 1796, English physician Edward Jenner determined that injecting a boy with pus from cowpox blisters (a mild disease transmitted by cows) prevented him from contracting the much deadlier smallpox. At first Jenner's discovery attracted doubt and ridicule but later he was proved to be right and vaccinations became widespread. Incidentally, Jenner coined the word "vaccine" from the Latin word for cow, vacca [source: BBC].
There is no doubt that humans are living longer and healthier lives thanks to the development of vaccines. Most people alive today would not have been around during the time when polio paralyzed between 13,000 and 20,000 people each year or whooping cough killed 9,000 or more children [source: CDC]. The Centers for Disease Control and Prevention (CDC) recommends that children from birth to 6 receive at least 14 different immunizations in the first few years of life. And most parents oblige – each year babies in the U.S. receive more than 10 million vaccinations [source: History of Vaccines]. Some people believe that vaccines, or perhaps the methods used to administer them, are linked with autism or other serious conditions, though current evidence does not support this [source: CDC].