They are the same.
To quote the C++11 standard (or the draft to be specific):
A typedef-name can also be introduced by an alias-declaration. The identifier following the using keyword
becomes a typedef-name and the optional attribute-specifier-seq following the identifier appertains to that
typedef-name. It has the same semantics as if it were introduced by the typedef specifier. In particular, it
does not define a new type and it shall not appear in the type-id.
I think the “the same semantics as the typedef specifier” say it all.