Search for Highly Effective Bird Flu Vaccine Goes On
Thursday, April 19, 2007; 12:00 AM
THURSDAY, April 19 (HealthDay News) -- This week's approval by the U.S. Food and Drug Administration of a less-than-perfect vaccine against bird flu is only the beginning of the search for a truly effective shot against the virus, experts said.
Luckily, the annual search for a vaccine against seasonal flu is helping scientists as they seek immunization against its much deadlier cousin, H5N1 avian influenza.
"The two [efforts] go hand in hand," explained Dr. Roland A. Levandowski, chief of the influenza, SARS and other viral respiratory disease section at the National Institute of Allergy and Infectious Diseases. "You can't just all of a sudden manufacture an [avian] vaccine if you don't know how to make the seasonal vaccine. The hurdle for all vaccines is to demonstrate that they're safe and effective."
But big challenges remain.
According to Levandowski, there are vaccine products at all different levels of development for both seasonal and avian flu strains.
On Tuesday, the FDA approved the first bird flu vaccine for use in humans.
That vaccine, developed by drug maker Sanofi Aventis, is far from perfect, however, and was described as an "interim measure" by Norman Baylor, director of the FDA's Office of Vaccines Research and Review. According to the FDA, only 45 percent of people who received the vaccine produced infection-fighting antibodies to the virus.
That's much lower than the regular seasonal flu vaccine, making it unclear as to how effective the newly approved bird flu shot would be in the event of an epidemic.
"There's no way to know how effective this will be in practice," said Philip Alcabes, an epidemiologist and associate professor at the School of Health Sciences of Hunter College in New York City. "That's unlike the situation in seasonal flu, where we know from last year and the year before and the year before roughly how much protection you get from the vaccines. We have no way of knowing that from a new vaccine, because the epidemic hasn't happened."
It's also difficult to predict safety with any accuracy in a clinical trials setting. A 1970s vaccine developed for swine flu posed no problems in 100,000 volunteers but caused severe reactions in one in every 500,000 people once it went public, said Dr. Paul K. Carlton Jr., USAF (Ret.) and director of the Texas A&M Health Science Center Office of Homeland Security.
In the past two years, the H5N1 strain of avian flu has infected poultry throughout Southeast Asia, Central Asia, Africa and Europe, prompting the destruction of millions of birds. So far, more than 100 people have died worldwide from H5N1 infection, which has been spread through close contact with birds.
The big worry among health officials is that the virus will acquire the ability to jump easily between humans, leading to a pandemic and millions of deaths. Unlike the seasonal flu, humans have no immunity to bird flu.