New Bird Flu Vaccine Nears Human Tests
DNA-Based Vaccine Could Be Ready Fast if Flu Pandemic Hits
Jan. 30, 2006 -- A new bird flu vaccine promises broad protection against
bird flu -- even if the virus mutates.
In animal tests, the genetically engineered vaccine protects chickens and
mice against the deadly H5N1 bird flu virus, the strain that has killed people
in Asia and Europe.
Human safety tests are poised to start in just a few months, says University
of Pittsburgh researcher Andrea Gambotto, MD.
"We are ready to go," Gambotto tells WebMD. "We are ready to
start production of vaccine for human trials. In a couple of days, we expect to
hear from the federal government about funding for clinical production. Four to
six months after that, we can begin human trials."
Vaccines and Virus Mutations
It's not your dad's flu vaccine. Normal flu vaccines -- including the bird
flu vaccine now in limited production -- are made from inactivated flu virus
grown in hens' eggs. It's a tried-and-true technology that's been around for
But inactivated flu vaccines work only against the exact virus strain they
are made from. If a flu virus mutates even slightly -- what experts call
genetic "drift" -- the vaccine won't work. That's why the seasonal flu
vaccine has to be changed every year or so.
Also, it takes longer to grow vaccine viruses in eggs than it does to grow
them with more modern cell-culture techniques. And in the case of bird flu, to
which humans have no pre-existing immunity, vaccine protection may take at
least two shots given weeks apart.
How the New Approach Works
Gambotto's team uses a different approach. Instead of making a vaccine from
pieces of killed virus, the researchers use a common cold virus -- adenovirus
-- genetically engineered to carry bird flu DNA. When given by nose spray or
injection, these vaccine viruses infect human cells. They go through a single
round of replication, during which they "express" pieces of bird flu
These pieces of bird flu virus do two things. One is to stimulate production
of antiflu antibodies. These antibodies quickly form a first line of defense
against flu infection and disease.
The second thing they do -- something the current inactivated vaccine does
not do -- is stimulate antiflu T-cell immunity. This long-lasting form of
immunity offers a second line of defense. And it may offer protection against
drift variants of the virus used in the vaccine.
"In humans, the H5N1 bird flu takes about two weeks to kill, so there is
time for T cells to come out and give protection," Gambotto says.
Will It Work?
Adenoviruses induce very powerful immune responses, says flu expert John
Treanor, MD, director of the vaccine and treatment evaluation unit at the
University of Rochester in New York.
"Applying this to an H5 bird flu vaccine makes a lot of sense,"
Treanor tells WebMD. "Gambotto's team shows it can be quite protective in
the mouse model. ... That is interesting because this could be a pathway toward a
more broad-based vaccine that could protect against all viruses in the H5