Liposomal Influenza Vaccine

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Very large academic studies in the US have established that influenza A and B vaccines (mainly subunit preparations) prevent hospitalisations and deaths in ‘at risk’ groups such as the elderly. Greater confidence in vaccine efficacy has resulted in the use of increased amounts of the vaccines in Europe and the US. In the UK, a record 8 million vaccine doses were manufactured during 1998. However, currently available vaccines induce protection in 70 to 80%, rather than 100%, of patients. Antigenic drift of the haemagglutinin (H) and neuraminidase (N) antigens affects the immunogenicity of influenza vaccines, but even with a good antigenic match between vaccine and virus, there is margin for improvement. Also, some elderly persons, fortunately in a minority, are ‘nonrespondent’ to certain viral strains. It is important to evaluate the data for liposomal influenza vaccine against this background. Liposomes are lipid particles that can serve as delivery systems and adjuvants for antigens. They are biodegradable if composed of phospholipids. In the case of liposomal influenza vaccine, the liposomes (or so-called ‘virosomes’) are novel structures of liposome bilayers into which are inserted influenza H and N antigens; the vaccine has a similar appearance to an influenza virus. Obviously the current studies with the novel liposomal influenza vaccine are still limited with respect to the number of patients who have received the vaccine, but the data look solid and significant. I was particularly impressed with the immune response to a single dose of the liposomal vaccine in children, who would often be unprimed to influenza. Similarly, I appreciated the comparison with whole virus vaccine which is often a good immunogen but which unfortunately also induces unwanted systemic responses, particularly in children. It would seem that by removal of viral egg lipids and RNA and nucleoprotein and matrix proteins, followed by reconstitution of H and N into liposomes, the immunogenicity of liposomal influenza vaccine is improved compared with conventional influenza vaccines, but without the adverse effects of whole virus vaccines. The scientific progress of the new liposomal vaccine will be followed with acute interest. ▲ GUEST COMMENTARY BioDrugs 1999 Feb; 11 (2): 145-146 1173-8804/99/0002-0145/$01.00/0