Smallpox

In 2007, a boy got a “smallpox-like” reaction from his father’s smallpox vaccine. (1) Which is curious. Because that vaccine is not made from smallpox, it is made from vaccinia. “Although the exact origins of vaccinia virus are uncertain, vaccinia may represent a hybrid of the variola and cowpox.”(2) So what disease did the boy get, then?
Sources:
(1) http://emedicine.medscape.com/article/231773-overview
(2) http://www.reuters.com/article/2007/05/18/us-smallpox-boy-idUSN1744524120070518

To view all Smallpox Vaccine reactions reported to the Vaccine Adverse Event Reporting System through July 7, 2013, cut and paste this web address into your own browser:

http://medalerts.org/vaersdb/findfield.php?TABLE=ON&GROUP1=AGE&GRAPH=ON&GROUP6=VACY&EVENTS=ON&VAX[]=
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