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New Vaccine Designed for a Deadly Flu Strain

U.S. Officials Prepare for Next Year's Flu Season
WebMD Health News

Feb. 18, 2005 -- In a two-day meeting held in Washington earlier this week an FDA Advisory Committee voted to change next year's flu vaccine to include protection against the potentially deadly "California A" strain, reportedly one of the most lethal flu infections to have surfaced in many years.

First isolated in Santa Clara, Calif. last September, it has so far been responsible for up to 20% of the flu cases diagnosed this year. In January the CDC officially identified it as "A/California" -- and they say it's on a dangerous rise.

"Based on the isolates and what the surveillance shows we are seeing more and more of California A already; it is steadily going up every week in the United States and it is a great cause for concern," says Dave Daigle, spokesman for the CDC, in attendance at the FDA's vaccine meetings.

"It's important that it goes into next year's vaccine; it could save a lot of lives," says Daigle.

Indeed, in line with recommendations made earlier this month by the World Health Organization, the flu vaccine for 2005-2006 will include not only protection against California A, but also the "New Caledonia" and "B Shanghai" strains.

Different types of influenza viruses circulate each year. A virus type that appears in one year does not necessarily show up the following year. Influenza A and B are the two types of influenza viruses that cause epidemics in humans. Influenza A viruses are further broken down into subtypes based on surface antigens known as H and N.

Antigens from "New Caledonia" and "B Shanghai" strains of the influenza virus were present in the 2004-2005 flu season. Each vaccine can contain protection against only three strains. These three viruses will be used because they represent influenza viruses that will likely circulate during the 2005-2006 flu season.

"We are limited by volume as to how much can be put in and how effective it will be," says Daigle.

Of the three, health officials are most concerned about California A, which is a strain belonging to a family of Influenza A H3N2. It is believed to be among the most deadly of all flu strains. A slightly different strain of H3N2 -- not included in the current 2004 vaccine -- was blamed for the deadly disease outbreak that swept through Colorado and other western states earlier this year.

"Wherever you see H3N2 you are going to see life-threatening complications. It is a deadly strain with more hospitalizations and more deaths than any other type of flu virus," says Mary Jo DiMilia, MD, assistant professor of medicine at the Mount Sinai School of Medicine in New York City.

At greatest risk, says DiMilia, are the elderly, children, and those with weakened immunity, such as HIV infection or those with organ transplants on drugs which suppress the ability of the immune system to fight infection. Patients undergoing chemotherapy are also at risk.

"Truthfully, H3N2 is so dangerous, everyone is at risk -- this is not a flu strain to be taken lightly," says DiMilia.

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