Xiaohui Li, Peter Pushko and Irina Tretyakova
Cases of H7N9 human infection were caused by a novel, avian-origin H7N9 influenza A virus that emerged in eastern China in 2013. Clusters of human disease were identified in many cities in China, with mortality rates approaching 30%. Pandemic concerns were raised, as historically, influenza pandemics were caused by the introduction of novel influenza A viruses into the immunologically naïve human population. Currently, there are no approved human vaccines for H7N9 viruses. Recombinant protein vaccine approaches have advantages in safety and manufacturing. In this review, we focused on the evaluation of the expression of recombinant hemagglutinin (rHA) proteins as candidate vaccines for H7N9 influenza, with the emphasis on the role of oligomeric and particulate structures in immunogenicity and protection. Challenges in preparation of broadly protective influenza vaccines are discussed, and examples of broadly protective vaccines are presented including rHA stem epitope vaccines, as well as recently introduced experimental multi-HA VLP vaccines.