Sparrow knew that he didn't need them to be as vigilant as he was, especially since neither could engage in battle at the moment. Rose was injured, her breathing growing ragged as the virus began to infiltrate her brain through her bloodstream. Sparrow was determined to resolve the situation before Rose succumbed to the virus and turned into a zombie. He couldn't afford to divert his attention from the front, as any lapse in focus could lead to an immediate attack.
He reasoned that Rose could wait for the moment, as he and the other guy were now immune to the zombie virus after awakening their ability. Unless they faced an attack so fatal that it would cause instant death, they were confident in their survival. After all, they had been provided with vials of blue and black liquid for situations of serious danger.
