Scientists have used a common cold virus in lab mice to test a prototype vaccine against the H5N1 strain of bird flu.

Flu vaccines are traditionally made in hen's eggs. But H5N1 kills poultry, which could lead to a scarcity of eggs if the strain becomes deadlier and gains the ability to spread easily between people, triggering a pandemic.

There are three other disadvantages to creating flu vaccines in eggs:

  • It takes up to six months to produce vaccines in eggs.
  • The vaccines can't be stockpiled because it only works against one sub-type of a flu strain, which may mutate.
  • Egg-based vaccines aren't safe for people who are allergic to eggs.

The H5N1 strain is so lethal to poultry that it kills the chicken embryos.
The H5N1 strain is so lethal to poultry that it kills the chicken embryos.

Instead, researchers in the U.S. used human cold virus or adenovirus that was changed so it could not make copies of itself.

The genetically engineered virus delivered a prototype vaccine that seems to stimulate a more powerful immune response in animals compared to previous flu vaccines.

Two teams of researchers, one based at the University of Pittsburgh, the second at the U.S. Centers for Disease Control in Atlanta, targeted the main protein, or hemagglutinin, sticking out from the surface of the virus.

Mutations in hemagglutinin are why flu shots need to changed to work against the strain circulating each flu season.

Both teams found their prototype vaccines completely protected mice who were later exposed to H5N1 viruses isolated from people, compared to mice injected with a harmless saline solution.

In the case of the Pittsburgh team, the test vaccine also worked in chickens, they reported in last week's issue of the Journal of Virology.

Suryaprakash Sambhara of the CDC and his colleagues said their prototype cold virus vaccine seemed to not only induce antibodies like other vaccines, but also created a response from the immune system's T cells.

The T cell response may mean the vaccine could work against more strains of bird flu, allowing the vaccine to be stockpiled before a pandemic.

"This approach is a feasible vaccine strategy against existing and newly emerging viruses of highly pathogenic avian influenza to prepare against a pandemic," the CDC team wrote in the Feb. 2 online issue of The Lancet medical journal.

Researchers face several hurdles before the vaccine could be used in people, including more tests in lab animals and clinical trials in humans to show if it works and is safe.