Development of vaccines against influenza A virus (H5N1).

Three influenza pandemics took place during the 20th century, including the 1918 pandemic, which killed an estimated 50 million people. We are facing the threat of another pandemic, which may be caused by an A/H5N1 influenza virus. These viruses have expanded their territory from Asia to the Middle East, Africa and Europe and have caused more than 190 human deaths up to the present. Vaccines in response to this pandemic threat are currently under development. Reverse-genetics-based inactivated whole-virion vaccines and adjuvanted split-virion vaccines are undergoing clinical trials and are among possible candidates to be approved as H5N1 vaccines for human beings. Problems, including low immunogenicity in the generally naive human population, a lack of data on these vaccines in relation to immunocompromised Dr. Yhu-Chering Huang patients, young children and the elderly and the currently limited global capacity to manufacture influenza vaccines, all need to be resolved. Several innovative approaches, such as the use of novel adjuvants, an antigen-sparing policy and the use of adenoviral-vector-based or DNA vaccines, are being used to develop more efficient vaccines. Every effort should be made to shorten the gap that remains and improve greatly influenza pandemic vaccine access.