Scientists are claiming a breakthrough in the battle to produce a vaccine against the deadly H5N1 strain of bird flu. Their findings were published in an on-line report from The Lancet medical journal.
French scientists from the pharmaceutical company Sanofi Pasteur are developing a vaccine based on a modified strain of the virus.
An experimental vaccine has been produced and has passed its first clinical hurdle, with a phase one trial involving 300 volunteers proving conclusively that the vaccine can trigger a safe immune response in people.
Although there is no evidence yet that H5N1 can spread from person-to-person, a reliable vaccine will be a vital weapon if the virus mutates into a pandemic form. The virus is highly virulent, with a fatality rate of up to 70%.
Dr Melanie Saville and colleagues reported on an assessment of whether the vaccine is safe and capable of producing neutralising antibodies in humans.
In the trial, volunteers received one of six vaccine formulations at various doses with or without the addition of a “helper” adjuvant compound, aluminium hydroxide.
The scientists found that a two-dose regimen of 30 micrograms of the vaccine induced the highest antibody response after 42 days.
Vaccines given with aluminium hydroxide worked better than those without. However, the level of antibodies needed to offer protection against H5N1 was currently unknown.
In an accompanying article, US experts Dr Suryaprakash Sambhara, from the Centres for Disease Control and Prevention in Atlanta, Georgia, and Dr Gregory Poland, from the Mayo Clinic College of Medicine in Rochester, Maryland, warned that a vaccine powerful enough to hold back a pandemic was still lacking.
“We do not know if these vaccines are sufficient to protect individuals in the event of an influenza pandemic,” they wrote.
They added that vaccine stockpiling options were also limited with the new vaccine because two doses at 30 micrograms per dose were required. This restricted the number of doses of vaccine it was currently possible for global manufacturers to make.