Development of otitis media (OM) in juvenile chinchillas. (A) Adult chinchillas were immunized with adjuvanted PE, PilA, or PE-PilA or adjuvant alone. Sera were collected and used for passive transfer to juvenile chinchillas. Anti-PE and anti-PilA immune sera were combined to form the PE + PilA group. After passive transfer, the juvenile chinchillas were intranasally challenged with NTHi strain 86-028NP, and the development of otitis media was monitored by video otoscopy and tympanometry for 35 days after bacterial challenge. *, P < 0.05; **, P < 0.01; ***, P < 0.001 for PE + PilA versus AS04. (B) Adult chinchillas were immunized with adjuvanted PE-PilA or adjuvant alone. Sera were transferred to juvenile chinchillas, and the animals were intranasally challenged with NTHi strain 86-028NP. The development of otitis media was monitored in a blind manner for 35 days after bacterial challenge. **, P < 0.01 for PE-PilA versus AS04.