His office has confirmed. Nate Silver points out:

Byrd’s current term expires on January 3, 2013. Under West Virginia state law on handling Senate vacancies, “if the vacancy occurs less than two years and six months before the end of the term, the Governor appoints someone to fill the unexpired term and there is no election”. Otherwise, Manchin would appoint an interim replacement, and an special election would be held in November to determine who held the seat in 2011 and 2012. In other words, we are within a week of the threshold established by West Virginia law. If a vacancy were to be declared on July 3rd or later, there would not be an election to replace Byrd until 2012.

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