US researchers are working on a new bird flu vaccine that could provide broader protection to people and be easy to produce in large quantities as well.
The vaccine protected mice from bird flu infection for more than a year and researchers are hopeful that similar results could be found in humans.
It is also broad enough to protect against some mutations of the virus, according to a study published in The Journal of Infectious Diseases.
"We want to have a vaccine that can be stored in advance and have the potential to provide protection for a period of time until we can change the vaccine to match the latest form of avian influenza," said study author Suresh Mittal of Purdue University.
"The combination of flu genes that we've used to produce the vaccine, I think, will provide that capability."
Mittal and his colleagues used a mutated version of a common cold virus to deliver genes from two types of the deadly H5N1 avian influenza.
This delivery system has a number of advantages.
Since their adenovirus is incapable of multiplying, people will not get sick from the vaccine.
It is also produced without the use of eggs, which become scarce during bird flu epidemics. This will lower costs and increase the speed at which the vaccine can be developed, Mittal said.
The vaccine also includes molecules which stimulate the body's immune system, allowing for the use of lower doses of the vaccine.
The molecules further allow the vaccine to be stockpiled, so more people can be vaccinated and helps the vaccine protect against new strains of H5N1.
The H5N1 strain of bird flu has killed 240 people worldwide since late 2003, according to the World Health Organization.
Experts fear the virus, which is usually spread directly from birds to humans, could mutate into a form easily transmissible between people, sparking a deadly global pandemic.
The only vaccine currently approved by US health officials requires a very high dose, only works in about 60 percent of those immunized and does not protect against new strains of the H5N1 virus.