Smallpox is a potentially life-threatening illness caused by the variola virus.  Because humans are the only known reservoir, naturally occurring smallpox was eliminated on the Earth in 1977--except for various stores of the virus in labs around the world.   A patient exposed to cowpox (vaccinia) is protected against smallpox infection.   The US and other military organizations routinely vaccinate against smallpox with vaccinia by injecting a small amount under the skin on the upper arm.


JAMA Derm 2015;151;13 and 482.

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