Everyone Needs Seasonal Flu Vaccination, CDC Advisers Say

[April 1, 2010, AJHP News]

Kate Traynor

BETHESDA, MD 12 March 2010—Seasonal influenza vaccines should protect against the pandemic 2009 H1N1 virus, and every American over the age of six months should receive a vaccine starting this fall, advisers to FDA and the Centers for Disease Control and Prevention (CDC) declared in February.

The recommendation to include a pandemic H1N1 component in vaccines for the 2010–11 flu season was made unanimously on February 22 by FDA's Vaccines and Related Biological Products Advisory Committee.

Federal officials at the meeting said that the pandemic-causing virus is essentially the only H1N1 virus currently circulating and has caused the vast majority of influenza cases over the past year.

Nancy Cox, director of CDC's Influenza Division, told FDA officials that H1N1 samples analyzed by the agency have proved "very homogeneous" and remain a good match to the strain used to produce monovalent H1N1 vaccines for 2009–10.

The other strains recommended for the U.S. trivalent vaccine are the same influenza H3N2 and B virus components in vaccines produced for the Southern Hemisphere's 2010 influenza season.

CDC's Advisory Committee on Immunization Practices (ACIP), during a February 24–25 meeting, shifted away from the risk-group-focused recommendations made in the past regarding which U.S. populations should be vaccinated against flu each year.

Vaccination is now recommended for all Americans except those for whom the vaccine is contraindicated and infants under six months of age. No U.S.-licensed influenza vaccine is intended for use in that age group.

According to CDC, about 85% of Americans were already targeted for vaccination during the 2009–10 flu season. The revised recommendation "seeks to remove barriers to influenza immunization and signals the importance of preventing influenza across the entire population," the agency announced after the meeting.

CDC stated that experience gained during the H1N1 pandemic, which strongly affected adults ages 19–49 years, influenced the decision to recommend routine vaccination for that age group.

Each year's trivalent influenza virus vaccine formulation contains components from two type A influenza viruses—an H1N1 and an H3N2 strain—plus an influenza B virus strain of either the Yamagata or Victoria lineage.

Experts historically have had a poor record predicting which influenza B viruses will cause disease in the months ahead, since both lineages may circulate during an influenza season.

Michael Decker, chief medical officer for Sanofi Pasteur, said during the FDA meeting that in 6 of the past 11 flu seasons, the virus type chosen for U.S. vaccines did not match viruses circulating during those seasons.

"We would do better flipping a coin" to select a type B strain, he said.

Last year, Decker suggested that FDA's advisers consider recommending a primary and a secondary type B virus so that manufacturers could produce limited batches of influenza virus vaccine against both type B lineages [see April 1, 2009, AJHP News].

At this year's FDA meeting, Decker presented safety and efficacy data from a preliminary study of a quadrivalent influenza virus vaccine formulation containing antigens from a Victoria- and a Yamagata-lineage B virus and two influenza type A viruses.

The final formulation was identical to that used in the 2009–10 flu season except for the addition of antigen from the type B virus from the previous season's vaccine. A preliminary study in adults measured the serologic response and safety profile of the vaccine.

"As expected, the addition of a second B strain did not pose any safety or immunogenicity issues," Decker said.

He said Sanofi plans to begin a trial of quadrivalent vaccine in children soon and seek eventual licensure of the vaccine as part of the company's Fluzone product line.