Preliminary results from the first study of CSL’s pandemic H1N1 vaccine show an immune response in adults that correlates with the prevention of influenza infection following a single 15mcg dose.

The study involving 240 healthy adults aged 18 to 64 years also found the vaccine has a similar side effect profile to that of seasonal influenza vaccines. Participants were randomised into two dose groups. Each participant received an initial vaccination followed by a second vaccination three weeks later. The first group received 15mcg of vaccine, the standard dose used for seasonal influenza vaccine, and the second group received 30mcg of vaccine. Blood samples were taken three weeks after each dose.

Preliminary data after the first vaccination demonstrated that post-vaccination antibody titres of 1:40 or greater were achieved in 96.7% of participants receiving the 15mcg dose and in 93.3% of participants receiving the 30mcg dose.

The study is being published online in the New England Journal of Medicine at www.nejm.org

(updated 3.20pm AEST, Monday 14 September)

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Associate Professor Raina MacIntyre is Professor of Infectious Diseases Epidemiology and Head of the School of Public Health and Community Medicine at the University of NSW. She sits on the Scientific Influenza Advisory Group to the Chief Medical Officer of Australia and is an expert in influenza and emerging infectious diseases.

“It is good news that one dose of vaccine appears to be sufficient to induce immunity against H1N1 09. The study also identified that a significant proportion of the population, including younger people, have pre-existing immunity to the virus. This could be due to exposure to related viruses in the past, or to H1N1 09 this year. Because influenza vaccine is time consuming to produce, it is encouraging that we may be able to use a one dose strategy using a standard dose (instead of 2 doses at higher antigen content as expected) to protect the population.”

Professor David Smith is Clinical Professor in the Faculty of Life and Physical Sciences and Faculty of Medicine, University of Western Australia, and the Division of Microbiology and Infectious Diseases, PathWest Laboratory Medicine. He is a member of the Influenza Specialist Group and the Australian Influenza Pandemic Planning Committee.

“The current issue of the New England Journal of Medicine provides exciting and encouraging data on the likely effectiveness of two new vaccines against the pandemic H1N1 (swine flu) virus using internationally accepted standards for measuring protection against influenza. One of these is the CSL-produced vaccine that has been purchased by the Australian government. This vaccine is made in the same way as our normal seasonal influenza vaccines and, in the age groups included in this study, it provided very good protection against the pandemic strain of influenza. It is particularly encouraging that these good responses occurred after a single dose of vaccine, indicating that people will be protected within 1-2 weeks of receiving the vaccine. It is possible that some sections of the population will only need a single dose of the vaccine, but that needs to be considered further.”

Dr Alan Hampson is an influenza consultant and Chair of the Australian Influenza Specialist Group

“The study showed that a very high percentage of the adult recipients produced a good antibody response, which should provide a high level of protection, to a single dose of vaccine made by conventional methods and formulated at the usual potency. This is great news as it means that available vaccine supplies will go much further than might have been anticipated and that protection can be achieved with a type of vaccine that has a long history of safe and effective use. It had previously been thought that two vaccine doses may be required or even that the conventional vaccines used each year may be poorly effective. The data also suggests that previous experience with viruses of the same subtype, even though quite distantly related as in the case of the current H1N1 outbreak, can prime the immune response so that a single dose of a pandemic vaccine can be effective. This may have important implications for the way that we might be able to respond to future, potentially far more severe, influenza pandemics.”

Professor Robert Booy is Head of Clinical Research at the National Centre for Immunisation Research & Surveillance (NCIRS) based at the University of Sydney.

“This is indeed very encouraging and perhaps as good as we could have hoped for in that it appears only one dose of vaccination is required, at a standard antigen level of 15mcg, to induce protective antibody concentrations in adults. It is important too that the safety profile is good. Results in children are keenly awaited”