Why did doctors and scientists develop vaccines in the first place?

Short Answer

Before vaccines were invented and widely used, disease outbreaks caused massive public health crises around the world that killed thousands of people at a time, sometimes decimating whole towns. Many other people who survived the diseases were left with permanent, often debilitating injuries and side effects. To prevent mass casualties and lifelong damage caused by diseases like polio, measles, malaria, and others, doctors and scientists began to study ways to prevent people from catching diseases in the first place. They started by developing a vaccine for smallpox, a disease that was responsible for thousands of deaths on nearly every continent throughout the 1700s.



Military research programs throughout history have made significant contributions to medicine and, in particular, to vaccine development. These efforts have been driven primarily by the effects of infectious disease on military conflicts: smallpox devastated the Continental Army in 1776, as well as troops on both sides of the United States Civil War; typhoid fever was common among soldiers in the Spanish-American War. More person-days were lost among U.S. soldiers in malaria-endemic regions to malaria than to bullets throughout the entire 20th century; indeed, malaria continues to sap military strength into the current century.

To respond to these diseases and the many others that threaten both soldiers and the public, military forces have devoted significant time and effort toward public health methods and medical research.

For a better understanding of the toll vaccine-preventable diseases took on the United States, and the tragedy they still cause in other parts of the world, visit our interactive timeline.


Smallpox was a scourge of the American Colonies, decimating Native American populations and then playing a part in the Revolutionary War. British soldiers had better immunity to the disease than the Colonial troops, and may have even used it as a weapon. In 1776, half of the 10,000 Continental Army soldiers around Quebec fell ill with smallpox; of the outbreak, John Adams wrote, “The smallpox is ten times more terrible than the British, Canadians, and Indians together. This was the cause of our precipitate retreat from Quebec.”

The following year, George Washington, as commander-in-chief of the Continental Army, ordered mandatory inoculation against smallpox for any soldier who had not gained prior immunity against the disease through infection. The procedure in that era was known as variolation, intentionally exposing someone to a mild form of the smallpox virus (Jenner would not develop the smallpox vaccine until 1796).  For the British Army in the North American colonies, inoculation was voluntary.

As a result of Washington’s orders, the Continental Army was the first in the world with an organized program to prevent smallpox. Some historians have suggested that if smallpox inoculation had been performed earlier, the smallpox outbreak among Continental soldiers in Quebec could have been avoided—speeding up the conclusion of the Revolutionary War and potentially allowing for the addition of some or all of the British colony of Canada to the United States.


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