# 764
Helen Branswell of the Canadian Press brings us another excellent article, this time on the unknowns we face when trying to devise an effective vaccine for the H5N1 virus. As always, her work is top notch.
Amid bird flu vaccine debate, scientists aren't sure what dose will protect
HELEN BRANSWELL
(CP) - Concerns about the developing world's access to affordable pandemic vaccines are expected to take centre stage this week at the World Health Organization's annual general meeting, the World Health Assembly.
But as global health leaders struggle to ensure pandemic vaccines won't just be a tool for wealthy countries, influenza scientists admit they face an enormous conundrum, one that could stand in the way of efforts to transform vaccine for the few into vaccine for the many.
Simply put, scientists can't be certain how much vaccine is needed to protect people against novel influenza viruses such as H5N1 avian flu, because they don't know what the immune system of a person protected against a new flu strain would look like.
Sure, they can observe whether immunization with H5N1 vaccine produces certain antibodies and to what levels the antibodies rise, but they have no way of gauging how much protection those antibodies will provide if the person is exposed to the virus.
"We can't get the answer to that until the pandemic comes. There's just no way," admits Dr. Robert Webster, the renown flu researcher from St. Jude Children's Hospital in Memphis, Tenn.
The uncertainty about what protection against H5N1 actually looks like is bedevilling ongoing debates over whether people should be pre-vaccinated against the virus or whether a program of ultra-low or single dose vaccines could be safely used to stretch limited supplies and protect millions more people.
"There are two very bad scenarios. And it's not that anybody's wrong or right, it's just that the science isn't there," explains Dr. Jesse Goodman, director of the branch of the U.S. Food and Drug administration that assesses and licenses vaccines.
"So one bad scenario is that if you could have used less (vaccine per person) and you didn't have enough doses and you didn't use less. Less people are protected. But an equally bad scenario is you cut a dose to a certain thing and it doesn't protect anyone."
"The truth is probably somewhere in between. And the science . . . to get there is not going to be trivial."
