Bird Flu Vaccine Works in Humans
But if Mutant Flu Comes, Will Vaccine Match?
Bird Flu Mutant Might Mean New Vaccine
The new bird flu vaccine is based on a bird flu virus isolated directly from an infected person in Vietnam. The good news, Treanor says, is that this bird flu virus is very much like the virus seen in people with more recent bird flu infections. This means the vaccine likely would work against current bird flu virus infection.
However, Treanor and Fauci both say there's no guarantee that this vaccine will work against a bird flu virus that makes the genetic changes needed to spread easily among humans.
"If the virus does evolve, this current vaccine may not be protective," Fauci says. "You would have to substitute for the currently circulating virus. But even if you have to change vaccines later on, we now know how to do it. This puts us months ahead. This is not the end. But it is an important first step."
How Much Time Needed to Prepare Vaccine?
Treanor estimates that if a pandemic flu virus did appear, it would take about six months to come up with a vaccine. Why so long? Flu vaccines are still made using a decades-old process requiring millions of sterile chicken eggs. Newer technologies exist but have not yet been fully tested or licensed.
"It is important that we have been able to go through the process of making an H5N1 bird flu vaccine," Treanor says. "It is a dry run. Going through every step lets us encounter all the unforeseen difficulties you might encounter in a pandemic situation. We are far ahead of where we would have been if we were starting from scratch."
The promising early findings are based on 113 people vaccinated at the University of Rochester, UCLA, and the University of Maryland. An additional 350 people have also received the vaccine or placebo; those results are now being analyzed.
One drawback to the new vaccine is that it takes two doses given four weeks apart. That's no surprise. It takes two flu shots to vaccinate children for the first time. During flu season one shot annually is recommended because the flu shot is really a booster vaccination for those previously vaccinated or who have had the flu. Since few humans have ever had H5N1 flu infections before, full immunity will take two doses.
And doses are also a problem. Vaccination against bird flu is going to take a higher vaccine dose than is usual for flu vaccines. This means that a scarce vaccine supply can't be diluted to make more doses. Treanor says that researchers are testing vaccine ingredients called adjuvants -- alum, for example -- that boost immune responses and might stretch limited vaccine supplies.