New Bird Flu Vaccine a Shot of Hope
Faster-to-Make Vaccine May Protect Against Multiple Bird Flu Strains
June 11, 2008 -- A new, faster-to-make type of flu vaccine may protect against multiple bird flu strains, early studies in humans suggest.
Two shots of the new vaccine are given three weeks apart. The most effective dose of the vaccine elicited supposedly protective levels of antibodies in 76% of volunteers. Those antibodies neutralized the clade 1 H5N1 bird flu virus used in the vaccine.
But the vaccine also raised antibodies that neutralized a clade 3 H5N1 virus in 76% of volunteers, as well as antibodies that neutralized a clade 2 H5N1 virus in 45% of volunteers.
"A broadly reactive immune response to clade 2 and clade 3 of H5N1 virus can be obtained with the use of a low-dose clade 1 vaccine," conclude Baxter Bioscience researcher Hartmut J. Ehrlich, MD, and colleagues.
Just as exciting as the vaccine's broad effect is the fact that it's much faster to make than flu vaccines currently in use. Current vaccines must be grown in fertilized hens' eggs. This process takes 22 weeks. And it can start only seasonally, when the eggs are available.
The new vaccine, grown in green monkey cell lines long ago adapted for laboratory use, takes only 12 weeks to produce. That could be a huge advantage, given how quickly flu pandemics spread when a bird flu learns to spread easily from human to human -- something that has not happened since 1968.
Why does the new vaccine appear to be so widely protective? Traditional flu vaccines use purified bird flu virus proteins. The new vaccine uses a whole virus that has been killed by chemicals and ultraviolet light. Whole-virus vaccines usually are more capable of producing an immune response than vaccines using viral subunits.
Whole-virus vaccines also tend to cause more reactions in people receiving the vaccine, although this did not seem to be the case in the Ehrlich team's 275-person study. Mild pain at the injection site and headache were the most common side effects.
The biggest drawback to the new vaccine is that it must start with living, potentially deadly, wild-type strains of bird-flu virus. These viruses must be grown in biosafety level 3 laboratories.
"Could virus spread from a production facility and initiate an epidemic?" asks Dartmouth researcher Peter F. Wright, MD, in an editorial accompanying the Ehrlich report in the June 12 issue of the New England Journal of Medicine.
Wright notes that polio vaccines are still being made with whole virus, and that no virus has yet escaped. To protect their sterility, vaccine viruses are grown in closed systems -- a precaution that also limits the opportunities for the viruses to escape.