H3 Stalk-Based Chimeric Hemagglutinin Influenza Virus Constructs Protect Mice from H7N9 Challenge

The recent outbreak of H7N9 influenza virus infections in humans in China has raised concerns about the pandemic potential of this strain. Here, we test the efficacy of H3 stalk-based chimeric hemagglutinin universal influenza virus vaccine constructs to protect against H7N9 challenge in mice. Chimeric hemagglutinin constructs protected from viral challenge in the context of dif-ferent administration routes as well as with a generic oil-in-water adjuvant similar to formulations licensed for use in humans. In early spring 2013, the Chinese authorities reported the firsthuman cases of avianH7N9 influenza virus infections (1), and a total of 137 cases and 45 fatalities have been officially confirmed by the World Health Organization by 25 October 2013 (including 2 cases in October 2013) (2). Characterization of viral isolates re-vealed that H7N9 binds to 2.6-linked sialic acids and that it can replicate in the mammalian upper respiratory tract, indicating that it could be able to acquire sustained human-to-human trans-missibility (3–5). These findings, together with the fact that neur-aminidase (NA) inhibitor-resistantmutants have arisen quickly in treated patients, without apparent fitness loss (6), have generated concerns for an H7N9 pandemic