Current Advances in Developments of New Influenza Vaccines

We have been now experiencing the first pandemic in the 21st century by a 2009 novel influenza A (H1N1) virus infection. The use of effective vaccination is the most reliable prophylactic measures against influenza virus infection. Hemagglutinin (HA) of surface viral glycoproteins plays a principal role as immunogenecity induced by natural infection or vaccination in our bodies. A split-product vaccine is prepared from inactivated influenza virus particles of epidemic strains and used worldwide. However, the administration of inactivated vaccine is not always effective. The antigenicity of HA proteins is continuously changed according to mutations in its gene for escaping from host immune systems. Therefore, vaccination against epidemic strains with mutations is needed to repeat annually. Contrary to epidemic strains, it is difficult to propagate pandemic strains of influenza viruses owing to the virulence. Consequently, a sufficient quantity of antigen cannot be obtained. Thus, currently licensed influenza vaccine has a lot of inevitable problems. New developments for influenza vaccination, such as live cold-adapted vaccine, reverse genetics vaccine, DNA vaccine, universal vaccine and co-administration with adjuvant, have been tested in order to solve the problems. It is noted that the development of vaccine preparation using genetic engineering progressed rapidly. This article, therefore, reviews recent knowledge regarding (1) influenza virus HA, (2) currently licensed influenza vaccines, and (3) new devices for developing influenza vaccines.