Flu Viruses Change Each Year; Developing Updated Vaccines is Challenging

March 3, 2008

After a relatively mild beginning to this influenza season, the Centers for Disease Control (CDC) reported last week that 49 states, including Mississippi, were experiencing widespread flu activity.  Because of its impact on public health, the federal government commits significant attention and resources to battling this highly-infectious ailment.  This season has been particularly difficult as newly-emerging flu strains have diminished the effectiveness of this year’s vaccine.   

The CDC notes that flu activity began to increase in December and reports that cases have continued to rise through February.  It is hard to predict the severity of flu outbreaks from year to year due to the uncertainty about new viruses in circulation and the ability of the vaccine to counter them.  

                                NEW STRAIN EMERGED LATE
The spike in cases this year is due in large measure to new and evolving strains of the flu virus.  The flu virus changes from year to year, and vaccines are developed using the most prevalent strains of the virus from the previous season.  As a result, the current vaccine is said to be a good match for only about 40 percent of the viruses active now in the U.S. and around the world.   One of the most prevalent strains responsible for this year’s epidemic did not emerge until after scientists had ordered the vaccine in preparation for this season.

Flu vaccines have to be reconstituted each year, and there must be enough lead-time to produce more than 100 million doses before the next flu season.   The vaccine is approved in February to be available in the fall of each year.  One FDA official said, “Influenza viruses are changing all the time.  We try to have a window which allows us enough time to manufacture a vaccine, but we can’t just turn on a dime.”

                             DEDICATED HEALTH PROFESSIONALS
When I was a member of the House of Representatives, I served on the subcommittee that funded the government agencies tasked with fighting influenza and other infectious diseases.  I have seen first-hand the commitment our health care professionals have to protecting the American people from these public health threats.  Their record against influenza outbreaks over the past two decades has been impressive, having produced well-matched vaccines in 16 of the past 19 years.

The epidemiologists at CDC work closely with counterparts in the World Health Organization to track global flu activity.  They use the most advanced scientific methods to try and predict which strains will threaten the U.S. in the next flu season.  Armed with that information, they coordinate with the Food and Drug Administration to predict the strains that might pose a threat and then design the contents of the flu shot.

                                NEXT YEAR’S VACCINE APPROVED
Just last week, the FDA approved the vaccine for the 2008-2009 flu season, and it will include a complete reformulation of the inoculation.  This marks the first time in 20 years that all three flu strains comprising the vaccine have been replaced.   One influenza expert at CDC said surveillance methods and activities have been enhanced in the U.S. and around the world this year in efforts to meet this ever-changing challenge.  

While this year’s vaccine has not been as effective as planned, health officials say it is still providing some protection and will likely lead to a milder case if individuals contract the flu.  The CDC says it is also still a good idea for anyone classified as vulnerable to get a flu shot now, since the season could run as late as May.  Those individuals include children age six months to five years, pregnant women, anyone over 50, individuals with chronic medical conditions and nursing home residents.