What You Should Know for the 2013-2014 Influenza Season
Flu seasons are unpredictable in a number of ways. Although epidemics of flu happen every year, the timing, severity, and length of the season varies from one year to another.
Flu viruses are constantly changing so it's not unusual for new flu virus strains to appear each year. For more information about how flu viruses change, visit How the Flu Virus Can Change.
The timing of flu is very unpredictable and can vary from season to season. Flu activity most commonly peaks in the U.S. in January or February. However, seasonal flu activity can begin as early as October and continue to occur as late as May.
CDC recommends a yearly flu vaccine for everyone 6 months of age and older as the first and most important step in protecting against this serious disease. While there are many different flu viruses, the flu vaccine is designed to protect against the three main flu strains that research indicates will cause the most illness during the flu season. Getting the flu vaccine as soon as it becomes available each year is always a good idea, and the protection you get from vaccination will last throughout the flu season.
In addition, you can take everyday preventive steps like staying away from sick people and washing your hands to reduce the spread of germs. If you are sick with flu, stay home from work or school to prevent spreading influenza to others.
Flu vaccines are offered in many locations, including doctor’s offices, clinics, health departments, pharmacies and college health centers, as well as by many employers, and even in some schools.
Even if you don’t have a regular doctor or nurse, you can get a flu vaccine somewhere else, like a health department, pharmacy, urgent care clinic, and often your school, college health center, or work.
Visit the HealthMap Vaccine Finder to locate where you can get a flu shot.
A number of different manufacturers produce trivalent (three component) influenza vaccines for the U.S. market, including intramuscular (IM), intradermal, and nasal spray vaccines. See Key Facts About Seasonal Flu Vaccine for more information about the different types of vaccine available in the United States.
Most of the flu vaccine offered for the 2013-2014 season will be trivalent (three component). Some seasonal flu vaccines will be formulated to protect against four flu viruses (quadrivalent flu vaccines) and will be available as well according to manufacturers. All nasal spray vaccines are expected to be quadrivalent, however, this makes up only a small portion of total vaccine availability.
Flu vaccines are designed to protect against three influenza viruses that experts predict will be the most common during the upcoming season. Three kinds of influenza viruses commonly circulate among people today: Influenza A (H1N1) viruses, influenza A (H3N2) viruses, and influenza B viruses,. Each year, one flu virus of each kind is used to produce seasonal influenza vaccine.
The 2013-2014 trivalent influenza vaccine is made from the following three viruses:
- an A/California/7/2009 (H1N1)pdm09-like virus;
- an A(H3N2) virus antigenically like the cell-propagated prototype virus A/Victoria/361/2011;
- a B/Massachusetts/2/2012-like virus.
It is recommended that quadrivalent vaccines containing two influenza B viruses contain the above three viruses and a B/Brisbane/60/2008-like virus.
More information about influenza vaccines is available at Preventing Seasonal Flu With Vaccination.
Inactivated influenza vaccine effectiveness (VE) can vary from year to year and among different age and risk groups. For more information about vaccine effectiveness, visit How Well Does the Seasonal Flu Vaccine Work?
Multiple studies conducted over different seasons and across vaccine types and influenza virus subtypes have shown that the body’s immunity to influenza viruses (acquired either through natural infection or vaccination) declines over time. The decline in antibodies is influenced by several factors, including the antigen used in the vaccine, age of the person being vaccinated, and the person's general health (for example, certain chronic health conditions may have an impact on immunity). When most healthy people with regular immune systems are vaccinated, their bodies produce antibodies and they are protected throughout the flu season, even as antibody levels decline over time. People with weakened immune systems may not generate the same amount of antibodies after vaccination; further, their antibody levels may drop more quickly when compared to healthy people.
For everyone, getting vaccinated each year provides the best protection against influenza throughout flu season. It’s important to get a flu vaccine every year, even if you got vaccinated the season before and the viruses in the vaccine have not changed for the current season.
It's not possible to predict with certainty which flu viruses will predominate during a given season. Flu 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 flu viruses circulating during that season to evaluate how close a match there is between viruses used to make the vaccine and circulating viruses. Data are published in the weekly FluView.
In addition, CDC conducts studies each year to determine how well the vaccine protects against illness.
Yes, antibodies made in response to vaccination with one flu virus can sometimes provide protection against different but related viruses. A less than ideal match may result in reduced vaccine effectiveness against the virus that is different from what is in the vaccine, but it can still provide some protection against influenza illness.
In addition, it's important to remember that the flu vaccine contains three virus viruses so that even when there is a less than ideal match or lower effectiveness against one virus, the vaccine may protect against the other viruses.
For these reasons, even during seasons when there is a less than ideal match, CDC continues to recommend flu vaccination. This is particularly important for people at high risk for serious flu complications, and their close contacts.
CDC carries out and collaborates with other partners within and outside CDC to assess how well flu vaccines work. During the 2013-2014 season, CDC is planning multiple studies on the effectiveness of both the flu shot and the nasal-spray flu vaccine. These studies will measure vaccine effectiveness in preventing laboratory confirmed influenza among persons aged 6 months and older, since beginning in the 2010-2011 season the Advisory Committee on Immunization Practices (ACIP) recommended annual vaccination for everyone in this age group.
Information about vaccine supply is available on the CDC influenza web site.
Yes. If you get sick, there are drugs that can treat flu illness. They are called antiviral drugs and they can make your illness milder and make you feel better faster. They also can prevent serious flu-related complications, like pneumonia. For more information about antiviral drugs, visit Treatment (Antiviral Drugs).
Antiviral resistance means that a virus has changed in such a way that the antiviral drug is less effective in treating or preventing illness. Samples of viruses collected from around the United States and worldwide are studied to determine if they are resistant to any of the FDA-approved influenza antiviral drugs.
CDC routinely collects viruses through a domestic and global surveillance system to monitor for changes in influenza viruses. CDC will continue ongoing surveillance and testing of influenza viruses. Additionally, CDC is working with the state public health departments and the World Health Organization to collect additional information on antiviral resistance in the United States and worldwide. The information collected will assist in making informed public health policy recommendations.