Influenza vaccine development
Influenza is an acute respiratory illness that affects the upper and/or lower respiratory tract and is caused by influenza virus, usually of type A or B. Influenza circulates continuously, causing seasonal epidemics in temperate regions and year-round epidemics in some tropical regions. Influenza viruses are continuously changing, necessitating annual change in vaccine strains to better match with currently circulating influenza strains globally. Influenza A viruses may also cause pandemics characterized by rapid dissemination of a new, virulent influenza A subtypes to which there is little or no existing immunity.
Status of vaccine development
Immunization is the major public health measure for the prevention of influenza virus infection. There are numerous licensed seasonal influenza vaccines available, several of which have been prequalified by the WHO for purchase by UN agencies . There are also several vaccine candidates under development against animal influenza A viruses – influenza strains considered at greatest risk for causing a future pandemic.
For WHO, the development of vaccines against influenza viruses with pandemic potential, as well as seasonal influenza vaccines that induce broadly protective and long-lasting immune responses are high priorities.
Challenges to vaccine development
Due to the constant changing of circulating influenza viruses, influenza vaccines strains are changed annually (for both the Northern Hemisphere and the Southern Hemisphere) to more closely match currently circulating virus strains.