Process for the high-level expression of the outer membrane protein P2 of haemophilus influenzae type B (HIB-P2) in E.coli; purification process of the outer membrane protein P2 or fusion protein thereof, reduplication process of the outer membrane protein P2 or fusion protein obtained; substantially pure reduplicated P2 outer membrane protein from haemophilus influenzae type B (HIB-P2) or fusion protein thereof; vaccine comprising the outer membrane protein P2 of hamophilus influenzae type B (HIB-P2) or a fusion protein thereof; process for obtaining a P2 protein or P2-polysaccharide fusion protein conjugate; process to prevent bacterial meningitis in an animal; pNV-3 vector; pNV-2 vector, and pNV-6 vector