The first experimental bird flu vaccine made from lab-grown cells instead of chicken eggs shows promise in blocking the highly lethal virus, scientists report.
The advance is good news not just for preparations in case of a pandemic but also because it offers a way to make shots for seasonal flu much faster. That gives health officials crucial extra time to match annual shots to the flu strains circulating.
It also would reduce dependence on the old system of using millions of eggs to make flu vaccines and could cut production time in half, to as little as 12 weeks, said maker Baxter International Inc.
Results of midstage testing of the Baxter vaccine, Celvapan, showed two shots produced an immune response considered strong enough to protect 76 percent of healthy adults from both the H5N1 Vietnam strain it targets and the related Hong Kong strain; it seemed to protect 45 percent from a third, Indonesian strain.
"I think it is a big leap forward," said Wilbur Chen, a vaccine researcher at the University of Maryland School of Medicine who is not involved in the study.
Since the first outbreak in Hong Kong in 1997, more than 240 people in Asia, Europe and Africa have died from bird flu, which kills about two-thirds of people infected. Nearly all had close contact with poultry, but scientists worry bird flu could mutate to a form easily spread among people, who have no natural immunity. Many experts believe a pandemic will eventually occur.
Yesterday Hong Kong health officials ordered the slaughter of all live poultry in street markets due to one of the largest outbreaks of the virus in birds in years.
The United States has stockpiled 23 million doses of egg-based human bird flu vaccine made by GlaxoSmithKline P.L.C., Sanofi Pasteur Inc. and Novartis AG. Some European countries also have such stockpiles and are ordering Baxter's cell-based vaccine.
Other human vaccines - a few using cells or genetic engineering but most made from eggs - are being tested in dozens of government and commercial projects. Baxter officials say theirs is the first produced in cells that has been tested in people, and they expect to get a European Union license for Celvapan around year's end.
The company-funded study was reported in today's New England Journal of Medicine.
A total of 275 volunteers in Austria and Singapore got one of four doses. The best results - the 76 percent protection - came from the second-lowest dose.
That dose also proved effective in a final-stage test last year of 550 volunteers in Austria and Germany, said Harmut Ehrlich, head of research and development for Baxter's Vienna-based Bioscience unit. It protected 73 percent of adults under 60 and 74 percent of those over 60 from the Vietnam strain. It was less effective for the Indonesian strain and was not tested on the older Hong Kong one.
William Schaffner, a Vanderbilt University infectious-disease specialist, said that researchers needed to keep pursuing a better vaccine but that Baxter's had "pretty darn good results" at low doses.
"I'm excited about this," he said, "but we have not yet reached the finish line."
In the half-century-old egg method, virus samples are injected into hundreds of millions of specialized eggs and incubated. The egg fluids are later harvested, concentrated and purified into the vaccine.
With cell technology, small amounts of virus are put in large fermenting tanks with nutrients and cells derived from monkey kidneys, and the virus multiplies. Then the virus is inactivated, purified, and put into vaccine vials.