Fears of a potential pandemic due to A(H5N1) viruses have focussed new attention on our current vaccines, their shortcomings, and concerns regarding global vaccine supply in a pandemic. The bulk of current vaccines are inactivated split virus vaccines produced from egg-grown virus and have only modest improvements compared with those first introduced over 60 years ago. Splitting, which was introduced some years ago to reduce reactogenicity, also reduces the immunogenicity of vaccines in immunologically naïve recipients. The A(H5N1) viruses have been found poorly immunogenic and present other challenges for vaccine producers which further exacerbate an already limited global production capacity. There have been some recent improvements in vaccine production methods and improvements to immunogenicity by the development of new adjuvants, however, these still fall short of providing timely supplies of vaccine for all in the face of a pandemic. New approaches to influenza vaccines which might fulfil the demands of a pandemic situation are under evaluation, however, these remain some distance from clinical reality and face significant regulatory hurdles.
The ongoing epizootic of avian influenza due to A (H5N1) viruses, the growing count of associated human fatalities, and the fear that this may be the forerunner to a severe human pandemic have focussed new attention on the status, and in particular the shortcomings, of our current human influenza vaccines. It is now over 60 years since the demonstration that influenza viruses could be readily cultivated in the allantois of embryonated hens’ eggs and the subsequent application of this method of cultivation to prepare inactivated virus vaccines that were protective against infection.
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