By Steven Reinberg
TUESDAY, Aug. 5 (HealthDay News) -- With the memory of last season's flu vaccine mismatch still fresh, U.S. health officials announced Tuesday that they have approved vaccines for the 2008-09 season that include new strains of the virus most likely to circulate.
The U.S. Food and Drug Administration said it changed all three strains for this year's vaccine, which officials called an "unusual occurrence." Typically, just one or two strains are updated year to year. Two of the three strains recommended for the United States this year are now in use for the Southern Hemisphere's 2008 flu season, which is under way.
"One of the biggest challenges in the fight against influenza is producing new vaccines every year," Dr. Jesse L. Goodman, director of FDA's Center for Biologics Evaluation and Research, said in a news release. "There is no other instance where new vaccines must be made every year."
Each season's vaccines are altered to anticipate the virus strains most likely to be circulating. The closer the match between the circulating strains and the strains in the flu shots, the better the protection, officials said.
To puzzle out the best potential match, officials from the FDA, the U.S. Centers for Disease Control and Prevention, the World Health Organization and other institutions study virus samples and patterns collected throughout the year from around the world. Based on those forecasts, the FDA decides on the three strains that manufacturers should include in their vaccines for Americans.
The six vaccines for the 2008-09 season and their manufacturers are: CSL Limited, Afluria; GlaxoSmithKline Biologicals, Fluarix; ID Biomedical Corporation of Quebec, FluLaval; MedImmune Vaccines Inc., FluMist; Novartis Vaccines and Diagnostics Limited, Fluvirin; and Sanofi Pasteur Inc., Fluzone.
They are designed to protect against A/Brisbane/59/2007 (H1N1)-like virus; an A/Brisbane/10/2007 (H3N2)-like virus; and a B/Florida/4/2006-like virus, the FDA said on its Web site.
But, there's always the chance that the scientists' best guesses will fall short, as was the case during the 2007-08 flu season in the United States. Last year's flu season was the worst in four years, due, in part, to a vaccine that wasn't a good match for certain circulating flu strains, U.S. health officials said.
For strains of influenza A (H3N2) -- the most prevalent virus during the 2007-08 season, the vaccine was only 58 percent effective. And it was 100 percent ineffective against influenza B infections, leaving an overall vaccine success rate of about 44 percent, according to the U.S. Centers for Disease Control and Prevention.
Despite that 44 percent rate, it has been higher in some years and lower in others, Dr. Dan Jernigan, deputy director of CDC's Influenza Division, said during an April 17 teleconference. "In the last 20 seasons, 16 have had good matches, and there have been four that were less than optimal matches," he said.
Even if the vaccines and the circulating strains aren't an exact match, they will provide some protection and may reduce the severity of the illness or prevent flu-related complications, officials said.
A study published in the April 17 issue of Science could eliminate much of the guesswork, however. Researchers reported that flu viruses originate in East Asia and Southeast Asia, and it takes about eight to nine months before these new viruses reach western Europe and North America.
Jernigan said last spring that the CDC was involved in promoting better surveillance of emerging flu viruses in East Asia and Southeast Asia. The hope is that these surveillance efforts will lead to more effective and better-matched vaccines.
According to the CDC, each year from 5 percent to 20 percent of the U.S. population gets the flu. More than 200,000 people are hospitalized from flu complications, and about 36,000 people die from the disease. Some people, such as older people, young children, and people with certain health conditions, are at high risk for serious flu complications.