Universal Influenza Virus Vaccines That Target the Conserved Hemagglutinin Stalk and Conserved Sites in the Head Domain

Due to limitations of current influenza virus vaccines, new vaccines that mediate broad protection and show high efficacy against seasonal and pandemic viruses are urgently needed. The conserved stalk of the viral hemagglutinin has been identified as potential target antigen for this new generation of vaccines. A vaccination strategy based on chimeric hemagglutinin (cHA), which refocuses the immune response toward the stalk domain and the conserved neuraminidase, is currently being tested in clinical trials. Here we discuss how to improve the cHA antigens to generate vaccine candidates that both induce a broad antistalk response and target conserved immunosubdominant epitopes in the head domain of the hemagglutinin. These novel constructs, termed mosaic hemagglutinins, should provide enhanced protection and should be tested in clinical trials to assess their improved potential as universal influenza virus vaccine candidates.