The 2007-2008 Flu Season
NOTE: The information in this document is based on flu activity as of December 6, 2007. This document will be updated as needed as the flu season progresses.
What sort of flu season is expected this year?
Flu seasons are unpredictable in a number of ways. Although epidemics of flu happen every year, the beginning, severity, and length of the epidemic depends on many factors, including the different types and strains of influenza viruses circulating and whether the viruses in the vaccine match influenza viruses that are circulating.
The best way to prevent the flu is by getting a flu
vaccination
each year. Influenza activity in the U.S. has been low so far this season, but it is increasing. Flu activity typically does not reach its peak in the U.S. until January or February, making this a good time to get a flu vaccine. Flu activity can occur as late as May so getting a vaccine later in the season can still offer protection in most years.
Will new strains of influenza circulate this season?
Influenza viruses are constantly changing so it's typical for new strains of influenza viruses to appear each year. For more information about how influenza viruses change, visit
How the Flu Virus Can Change
.
What has the flu season been like in the United States so far?
So far during the 2007-2008 flu season, low levels of influenza activity have been reported in the United States. This is similar to the low levels of activity seen at this point in time during most years.
CDC’s Influenza Division collects, compiles and analyzes information on influenza activity in the United States each week from October through May. For more information about CDC’s surveillance and to access the weekly reports, visit
Flu Activity & Surveillance
.
How effective is the flu vaccine?
The effectiveness of the vaccine depends in large part on the match between the viruses in the vaccine and influenza viruses that are circulating in the community. If these are closely matched, vaccine effectiveness is higher. If they are not closely matched, vaccine effectiveness can be reduced. However, it’s important to remember that even when the viruses are not closely matched, the vaccine can still protect many people and prevent flu-related complications. Such protection is possible because antibodies made in response to the vaccine can provide some protection (called cross-protection) against different, but related strains of influenza viruses. For more information about vaccine effectiveness, visit
How Well Does the Seasonal Flu Vaccine Work?
Will this season’s vaccine be a good match for circulating viruses?
It’s not possible to predict with certainty which influenza viruses will predominate during a given season or what the severity, timing, or duration of a flu season will be. Influenza viruses are constantly changing (called drift) – they can change from one season to the next or they can even change within the course of one flu season. Experts must pick which viruses to include in the vaccine many months in advance in order for vaccine to be produced and delivered on time. (For more information about the vaccine virus selection process visit
Selecting the Viruses in the Influenza (Flu) Vaccine
.) Because of these factors, there is always the possibility of a less than optimal match between circulating viruses and the viruses in the vaccine.
Over the course of a flu season CDC studies samples of influenza viruses circulating during that season to evaluate how close a match there is between viruses in the vaccine and circulating viruses. In addition, CDC conducts vaccine effectiveness studies to determine the vaccine’s effectiveness. At this time, however, there has not been enough influenza activity to characterize how closely matched the vaccine will be to circulating viruses or how effective the vaccine will be. However, it’s important to remember that even during seasons when the vaccine is not optimally matched to predominant circulating viruses, CDC and other experts continue to recommend flu vaccine as the best way to protect against the flu.
Can the vaccine provide protection even if the vaccine is not a “good” match?
Yes, antibodies made in response to vaccination with one strain of influenza viruses can provide protection against different, but related strains. A less than ideal match may result in reduced vaccine effectiveness against the variant viruses, but it still can provide enough protection to prevent or lessen illness severity and prevent flu-related complications. In addition, it’s important to remember that the influenza vaccine contains three virus strains so the vaccine can also protect against the other two viruses. For these reasons, even during seasons when there is a less than ideal match, CDC continues to recommend influenza vaccination. This is particularly important for people at high risk for serious flu complications and their close contacts.
In what years was there a good match between the vaccine and the circulating viruses?
In recent years the match between the vaccine viruses and those identified during the flu season has usually been good. In 16 of the last 19 U.S. influenza seasons, the viruses in the influenza vaccine have been well matched to the predominant circulating viruses. Since 1988, in fact, there has only been one season (1997-98) when there was very low cross-reaction between the viruses in the vaccine and circulating viruses and two seasons (2003-04 and 1992-93) when there was low cross-reaction.
What are other actions that I can take to protect myself and my family against the flu this season?
A flu vaccine is the first and best defense against influenza. However,
antiviral drugs
are an important second line of defense against the flu. They can be used to treat the flu or to prevent infection with flu viruses. Treatment with antiviral drugs should begin within 48 hours of getting sick, and can reduce your symptoms and shorten the time you are sick. When used for prevention, antiviral drugs are 70% to 90% effective in preventing infection with influenza viruses. Two FDA-approved influenza antiviral agents are recommended for use in the United States to treat or prevent flu during the 2007-08 influenza season: oseltamivir and zanamivir.
In addition, you can take
everyday preventive steps
like frequent hand washing to decrease your chances of getting the flu. If you are sick with flu, reduce your contact with others and cover your cough to help keep germs from spreading.
