Five-week-old Syrian golden hamsters (8 animals per group) were infected intranasally with 10 6 PFU/animal of virus or placebo medium in 100 uL. Four days post infection, the nasal turbinates and lungs were harvested from 4 animals per group, homogenized and titered by plaque assay in Vero cells. On day 28 post infection, immunized hamsters were challenged with an intranasal dose of 10 6 PFU/animal of wthMPV/NL/1/00. Four days post-challenge, the nasal turbinates and lungs were harvested and assayed for challenge virus replication by plaque assay.