To determine if the lower level of replication in lungs and nasal turbinates of hamsters was sufficient to protect the hamsters from subsequent infection with hMPV, 4 hamsters were challenged with 10 6 PFU of wthMPV/NL/1/00 4 weeks post immunization. Four days post administration of the challenge, no virus was detected in either lungs or nasal turbinates of the immunized hamsters while unvaccinated animals had 5.6 +/-0.6 PFU/gm in URT and 4.5 +/-1.5 PFU/gm in the LRT (Table 2) . Therefore, replication of rhMPV/ΔM2-2 was restricted in hamsters and animals were protected from challenge with wthMPV/NL/1/ 00.