Newborns need a vaccination within the first day of life to prevent transmission of the virus from their mothers, and babies need two more doses within the first six months for full immunity.

VOA: standard.2010.07.26

So, you couldn't introduce the live virus in because that would cause the disease not just immunity.

所以 不可以直接接种活体病毒,因为这会使人致病而不仅是引起免疫应答

耶鲁公开课 - 生物医学工程探索课程节选

Head of the International Red Cross Federation's Influenza team, Robert Kaufman, says the impact of a novel virus on a community without immunity is not just about the number of illnesses and deaths.

VOA: standard.2009.09.04