Promising Bird Flu Vaccine produced in Monkey Cells

Baxter International’s new bird flu vaccine Celvapan was found to be effectual during experiments as it produced a satisfactory immune response in human trials.

According to a study published in Thursday's New England Journal of Medicine, the vaccine may provide protection against three variants of the deadly H5N1 virus, responsible for causing bird flu.

Two shots of the new vaccine are given with a gap of three weeks. The most effective dose of the vaccine brings forth supposedly protective levels of antibodies in 76 percent of the individuals.

The antibodies produced counteract the clade 1 H5N1 bird flu virus, which is used in the vaccine.

But the vaccine seems to have a broad range as it also elicited the levels of antibodies that neutralized a clade 3 H5N1 virus in 76 percent of volunteers, as well as antibodies that neutralized a clade 2 H5N1 virus in 45 percent of the people.

"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.

The vaccine does not need an adjuvant-- a substance that reinforces the effect of a vaccine. Lately, there have been safety concerns about adjuvants.

Another advantage of the vaccine is that it's much faster to make than the currently available flu vaccines. Current vaccines are cultured in fertilized hens' eggs, which requires about 22 weeks. And it can start only seasonally, when the eggs are available.

The new vaccine is grown in green monkey cell lines, which were adapted for laboratory use long time back and it takes only 12 weeks to produce.

One major drawback of the new vaccine is that unlike previous vaccines produced from purified bird flu virus proteins, it uses the whole virus, which tends to cause side effects in people receiving the vaccine.

Also, there is a risk of virus spread from production facility; so the viruses must be grown in biosafety level 3 laboratories.

Bird flu, which kills about two-thirds of people infected.

Since the first outbreak in Hong Kong in 1997, more than 240 people in Asia, Europe and Africa have died of the disease and nearly all had close contact with infected poultry.

Scientists fret because they believe the bird flu virus could mutate to a form which easily spreads among people, who have no natural immunity. Many experts believe a pandemic will eventually occur.

On Wednesday, Hong Kong health officials ordered the culling of all live poultry in street markets after the disease was confirmed in four markets.