Clinical Studies of Vaccines for Pandemic Influenza

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Although the study subjects were seronegative to the hemagglutinins in the vaccine viruses and were predicted to be susceptible to infection with the pLAIVs because the HA and NA genes were derived from novel influenza virus subtypes from avian/animal species, the vaccine viruses were highly restricted in replication. The immune responses to the pLAIVs were variable, ranging from high seroconversion rates to H9N2 and H7N3 to low seroconversion rates for H5N1, H6N1 and H2N2 vaccines. In order to pursue a live attenuated influenza vaccine strategy for influenza viruses with pandemic potential, it is important to learn more about factors that determine the level of replication of the pLAIV strains in seronegative healthy adults and factors that determine whether a vaccine recipient will develop an immune response to the vaccine. In FY13, we undertook a study to identify biomarkers that would that predict shedding and immune response to live attenuated influenza virus (LAIV) vaccines. This study would address the following questions: (1) Which biomarkers predict whether seasonal or pandemic LAIV replicate in the respiratory tract of healthy adults? (2) Which biomarkers predict whether seasonal or pandemic LAIV will elicit an immune response in healthy adults? These studies are in progress. We had previously evaluated H5N1 and H7N7 live attenuated influenza A virus vaccines in Phase I clinical trials at Johns Hopkins University and the University of Rochester; unfortunately, few vaccinees shed virus and/or seroconverted by hemagglutination inhibition or neutralization. However, a proportion of the vaccinees had other evidence (e.g. B cell ELIspot) of an immune response to the vaccine. We sought to determine whether the vaccinees were immunologically primed, and if so, would have a strong boost in their immune response to an inactivated H5 or H7 vaccine. This study would address the following questions: (1) Is there evidence of immunologic priming with a live attenuated H5N1 or H7N7 influenza virus vaccine that was highly restricted in replication and poorly immunogenic? (2) Does the H5N1 or H7N7 live attenuated influenza virus vaccine prime for an enhanced (and/or broad) immune response to the unadjuvated H7N7 inactivated virus vaccine? The analysis of the data from these studies is in progress.