A potential vaccine for the H5N1 bird flu virus helps protect healthy people at low doses, raising hopes for protecting millions of people if the virus mutates into a pandemic form.
A pandemic could be triggered if H5N1 or another deadly flu virus gains the ability to spread easily between people.
Chinese researchers tested the effectiveness of a vaccine that contains a modified version of the whole H5N1 virus, plus a booster to stimulate the immune system.
Vaccines made of whole viruses trigger a greater immune response than those using virus particles alone, allowing lower doses to be used, although there may be more side-effects.
"During a pandemic, the demand for influenza vaccines will far outstrip the manufacturing capacity of such vaccines, a situation that has led to [the World Health Organization] encouraging investigation into dose-sparing strategies," said study author Weidong Yin, CEO of Sinovac Biotech Co. Ltd., in Beijing.
No differences in side-effects
The 120 volunteers aged 18 to 60 were randomly assigned to receive two doses of the vaccine or a placebo at various doses.
After 56 days, all doses of the vaccine led to antibodies against the virus, with the 10-microgram dose showing the best response, the team reports in Thursday's online issue of the medical journal The Lancet.
The 10-microgram vaccine also met all European regulatory requirements for licensing a flu vaccine, and there were no differences in side-effects between the vaccine and placebo group.
"These findings identify a potential dose-sparing approach that could be crucial for a global supply of pandemic vaccine," infectious disease specialist Dr. Iain Stephenson of Leicester Royal Infirmary, U.K., said in a journal commentary.
If a pandemic occurs, experts say it will be easier to modify an existing vaccine for the pandemic strain if the safety of the vaccine design has already been shown.
The safety and effectiveness of two other potential H5N1 vaccines have been shown in early trials, one at a dose of 90 micrograms and the other at 30 micrograms.