An open label Phase I trial of a live attenuated H6N1 influenza virus vaccine in healthy adults.

BACKGROUND: We describe the results of an open label Phase I trial of a live attenuated H6N1 influenza virus vaccine (ClinicalTrials.gov Identifier: NCT00734175).

METHODS AND FINDINGS: We evaluated the safety, infectivity, and immunogenicity of two doses of 10(7) TCID(50) of the H6N1 Teal HK 97/AA ca vaccine, a cold-adapted and temperature sensitive live, attenuated influenza vaccine (LAIV) in healthy seronegative adults. Twenty-two participants received the first dose of the vaccine, and 18 received the second dose of vaccine 4 weeks later. The vaccine had a safety profile similar to that of other investigational LAIVs bearing avian hemagglutinin (HA) and neuraminidase (NA) genes. The vaccine was highly restricted in replication: two participants had virus detectable by rRT-PCR beyond day 1 after each dose. Antibody responses to the vaccine were also restricted: 43% of participants developed a serum antibody response as measured by any assay: 5% by hemagglutination-inhibition assay, 5% by microneutralization assay, 29% by ELISA for H6 HA-specific IgG and 24% by ELISA for H6 HA specific IgA after either 1 or 2 doses. Following the second dose, vaccine specific IgG and IgA secreting cells as measured by ELISPOT increased from a mean of 0.6 to 9.2/10(6) PBMCs and from 0.2 to 2.2/10(6) PBMCs, respectively.

CONCLUSION: The H6N1 LAIV had a safety profile similar to that of LAIV bearing other HA and NA genes, but was highly restricted in replication in healthy seronegative adults. The H6N1 LAIV was also not as immunogenic as the seasonal LAIV.