How vaccinations helped win the Revolutionary War

George Washington won the Revolutionary War not just by outsmarting and defeating the British Army. He also won it by successfully vanquishing what he referred to as another “most dangerous enemy”: smallpox.

And he did it by embracing science rather than by succumbing to fear.

In the winter of 1777, Washington decided to inoculate his troops against smallpox, despite the prevailing belief at the time among delegates to the Continental Congress and some of his own military doctors that doing so would lead to more, not fewer, deaths.

Washington’s decision turned out to be the right one. Not only did it save many lives, it also helped alter the course of the Revolutionary War.

As historian Thomas Shachtman (“Gentlemen Scientists and Revolutionaries: The Founding Father in the Age of Enlightenment”) points out in a 2014 article published in the Daily Beast: “Nothing that Washington did had a greater impact on the outcome of the war than his actions to protect his troops from death by smallpox.”

The leading killer

In the late 18th century, smallpox was the leading infectious killer in the American colonies, with a devastating death rate of up to 30 percent. A new outbreak had begun in 1775, ravaging both Boston and Philadelphia.

British troops tended to have immunity to smallpox, for most of them had already been exposed to the disease — and thus had developed immunity — back in England. 

But the same wasn’t true of Washington’s soldiers.

In 1776, “half of the 10,000 Continental troops dispatched to capture Quebec contracted the disease, forcing a hasty retreat,” explains Benjamin Drew, now a Harvard Medical School resident, in another article on the topic, which appeared in a 2015 issue of the journal JAMA Dermatology. “Some historians believe this tactical setback extended the Revolutionary War and is the reason Canada did not become an American colony.”

Washington had repeatedly asked the Continental Congress to lift its ban on variolation, the smallpox inoculation technique of that time. (It would be another two decades before Edward Jenner successfully tested his “cowpox” vaccine.) Variolation involved inserting pus from an infected person under the skin of an uninfected one. The inoculated person would develop a mild form of the disease, which would then immunize the person for a lifetime.

“Although championed by such scientific heroes as Benjamin Franklin, and undergone willing by John Adams, Thomas Jefferson, and other leaders, variolation was castigated as unsafe for the community because the patient had to be isolated for a week prior to the inoculation and two weeks or more after it,” explains Shachtman. “Congress had forbidden military doctors to administer it and forbidden army officers to take variolation or have their subordinates do it, on pain of being cashiered [dismissed].”

Washington did not undergo variolation himself, as he already had immunity to smallpox, having survived the disease as a teenager. His wife, Martha, was successfully inoculated, however — an outcome that Washington took as further evidence that the technique was safe and effective.

Seizing the moment

Finally, in January 1777, on the heels of his surprising victory at the Battle of Trenton and knowing that he had a few months before the fighting would pick up again, Washington decided “to seize the moment to unilaterally decree inoculation for smallpox as the policy of the army,” says Shachtman.

Washington was adamant on the issue, as is clear in a letter he wrote to his chief medical officer: “Necessity not only authorizes but seems to require the measure [inoculation against smallpox], for should the disorder infect the Army … and rage with its usual Virulence, we should have more to dread from it than from the sword of the enemy.” 

The mandatory inoculations were done in secret — small groups of men at a time — so as not to alert the British, who might have taken advantage of the situation had they known about it. Washington did write to the Continental Congress to tell them what he was doing, although he did not wait for their reply before issuing his order.

The inoculation campaign was remarkably successful. “Nearly 40,000 troops were inoculated,” writes Drew. “The following year, infection rates [in the Continental Army] fell from 17% to 1% — a landmark achievement representing the first successful case of inoculating an entire army against a disease.”

“Inoculating the American troops against smallpox effectively shielded Washington’s army from being decimated by disease until the arrival of foreign arms made it possible for them to turn the tide of battle in America’s favor,” adds Shachtman.

Have a happy — and healthy — Fourth of July. 

FMI: You can read Shachtman’s article, which is adapted from his book, “Gentlemen Scientists and Revolutionaries,” on the Daily Beast’s website. Drew’s article can be read on JAMA Dermatology’s website.