British drugmaker GlaxoSmithKline announced plans Thursday to open a new vaccine research center in Rockville by this fall, a project that could bring up to 700 new jobs to Montgomery County. The center — at the site of the former Human Genome Sciences, which Glaxo acquired in 2012 for $3.6 billion — would combine two Glaxo research facilities on the East Coast and is expected to employ 1,000 people by 2016, a company spokeswoman said.