FDA panel recommends flu vaccine changes for 2006/07

By Todd Zwillich

BETHESDA, Maryland (Reuters) – A U.S. Food and Drug
Administration advisory panel on Friday recommended changing
two of the three virus strains used in this year’s seasonal flu
vaccine for the 2006/07 flu season.

Experts on the panel voted unanimously to replace two of
this year’s strains because of surveillance data showing shifts
in the activity of viruses circulating in Europe and Asia.

They stressed that their recommendations represent a “best
guess” of what viruses will affect the United States in the
2006-2007 flu season. “Influenza viruses are inherently
unpredictable,” Nancy Cox, chief of the influenza branch at the
Centers for Disease Control and Prevention, told the panel.

The seasonal flu vaccine is known as a “trivalent” vaccine
because it contains three different virus strains. Each of the
strains is chosen for their ability to inhibit infection with
dozens of different but closely related viruses.

Viruses shift their potency and frequency each flu season.
Manufacturers alter the vaccine’s makeup each year to maximize
the chances that it will effectively protect humans.

Influenza causes an estimated 200,000 hospitalizations and
36,000 deaths per year in the United States, according to the
CDC.

The vast majority of cases are caused by Influenza A
viruses.

The FDA advisory panel voted to change the current
vaccine’s “California” strain of the H3N2 Influenza A virus to
a different H3N2 strain known as a “Wisconsin” strain. Experts
also recommended a shift from the less common “Shanghai”
Influenza B strain to a different B strain known as
“Malaysia/2506.”

The panel recommended no change to the current vaccine’s
“New Caledonia” strain of the H1N1 Influenza A virus.

The vaccine recommendations match others issued by the
World Health Organization earlier this week.

Manufacturers typically hope for few changes in the
vaccine. Changes mean more uncertainty in production, because
different strains grow at different rates during the
manufacturing process.

“Obviously it is a concern,” said Albert Thomas, director
of vaccine manufacturing for Sanofi-Pasteur, the largest U.S.
vaccine maker and a unit of French company Sanofi-Aventis. “It
does put more uncertainty into the total number of doses you’re
producing at any one time,” he told the panel.

But Kathleen Coelingh, senior director for scientific
affairs for FluMist manufacturer MedImmune Inc., said there
were few surprises in Friday’s recommendation. “Everyone has
been expecting this to happen based on the epidemiology we’ve
been seeing,” Coelingh said in an interview.

Less than 1 percent of all U.S. flu cases this year were
caused by Influenza B viruses. But experts are still
considering the possibility of recommending a “quadrivalent, or
four-strain, vaccine in the future that contains two types of
Influenza B virus.

That possibility has occupied expert vaccine panels for
years, and Friday’s committee recommended that the FDA convene
a new committee to discuss scientific data justifying the
manufacture of a four-strain vaccine.