Recombinant modified vaccinia virus Ankara expressing the hemagglutinin gene confers protection against homologous and heterologous H5N1 influenza virus infections in macaques.

Highly pathogenic avian influenza viruses of the H5N1 subtype have been responsible for an increasing number of infections in humans since 2003. More than 60% of infected individuals die, and new infections are reported frequently. In light of the pandemic threat caused by these events, the rapid availability of safe and effective vaccines is desirable. Modified vaccinia virus Ankara (MVA) expressing the hemagglutinin (HA) gene of H5N1 viruses is a promising candidate vaccine that induced protective immunity against infection with homologous and heterologous H5N1 influenza virus in mice. In the present study, we evaluated a recombinant MVA vector expressing the HA gene of H5N1 influenza virus A/Vietnam/1194/04 (MVA-HA-VN/04) in nonhuman primates. Cynomolgus macaques were immunized twice and then were challenged with influenza virus A/Vietnam/1194/04 (clade 1) or A/Indonesia/5/05 (clade 2.1) to assess the level of protective immunity. Immunization with MVA-HA-VN/04 induced (cross-reactive) antibodies and prevented virus replication in the upper and lower respiratory tract and the development of severe necrotizing bronchointerstitial pneumonia. Therefore, MVA-HA-VN/04 is a promising vaccine candidate for the induction of protective immunity against highly pathogenic H5N1 avian influenza viruses in humans.