Otherworlders by Angela Cavanaugh

SPSFC

When a virus threatens humanity with extinction, the desperate and dwindling number of uninfected seek refuge in a parallel universe. The technology is untested. The other universe is unprepared and one thing is made violently clear: they are not wanted. As a fatal virus mutates and threatens to kill all life forms on Earth, Special Agent Williams conspires to send the healthy away. After space travel and going underground are ruled out, all that remains is the theoretical technology of an autistic savant: escaping to a parallel universe. But when they travel to the other dimension, their arrival is met with suspicion and hatred. To evade persecution, experimentation, and to save their lives, the Otherworlders must find a way to escape, survive, and outwit Agent Williams's murderous double.