Health and Human Services Secretary Kathleen Sebelius said that a massive school closing wouldn't stop the spread of the swine flu virus, saying vaccinations must be the defense against a menace that one report said could infect up to half of the population. She said people should plan ahead for a potential outbreak, particularly those with pre-existing medical conditions, pregnant women, and healthcare industry workers. Sebelius said federal health authorities also are recommending that people should immediately get their regular "seasonal" flu vaccine to bolster their health for the scenario yet to play out later this year regarding the swine flu virus.