Vaccine - FAQs:

The influenza (flu) viruses selected for inclusion in the seasonal flu vaccines are updated each year based on which influenza virus strains are circulating, how they are spreading, and how well current vaccine strains protect against newly identified strains. Currently, 130 national influenza centers in 101 countries conduct year-round surveillance for influenza and study influenza disease trends. These laboratories also send influenza viruses to the four World Health Organization (WHO) Collaborating Centers for Reference and Research on Influenza located in Atlanta, Georgia, USA (Centers for Disease Control and Prevention, CDC); London, United Kingdom (National Institute for Medical Research); Melbourne, Australia (Victoria Infectious Diseases Reference Laboratory); Tokyo, Japan (National Institute for Infectious Diseases) for additional analyses.

The seasonal flu vaccine is a trivalent vaccine (a three component vaccine) with each component selected to protect against one of the three main groups of influenza viruses circulating in humans. (Last year's 2009 H1N1 vaccine was made in response to the pandemic first recognized in April 2009. Unlike seasonal flu vaccines, the pandemic vaccine protected against only one flu virus strain, the 2009 H1N1 virus.)

The influenza viruses in the seasonal flu vaccine are selected each year based on surveillance-based forecasts about what viruses are most likely to cause illness in the coming season. WHO recommends specific vaccine viruses for inclusion in influenza vaccines, but then each individual country makes their own decision for which strains should be included in influenza vaccines licensed in their country. In the United States, the U.S. Food and Drug Administration (FDA) determines which vaccine viruses will be used in U.S.–licensed vaccines.

For the 2011-2012 Flu Season, the H1N1 vaccine is included with the seasonal flu vaccine. In the future, the H1N1 vaccine will be included as long as it is active.

Each year, many labs throughout the U.S., and the world, collect influenza viruses from people who have the flu. Some of these flu viruses are sent to 1 of 4 World Health Organization (WHO) reference labs for detailed testing. These labs test how well antibodies made to the current seasonal vaccine react to the circulating virus and to new flu viruses.

Flu experts use these test results to predict what viruses will circulate in the population the following year. Then, 3 viruses are chosen to go into the flu vaccine for the following fall and winter:

• 2 subtypes of influenza A viruses; and
• 1 subtype of influenza B virus.

One or 2 of the 3 strains in the vaccine are usually changed each year.

On Mutation:

Clearly the issue that concerns us all is what if H1N1 evolves, mutates to remain a virus that spreads quite easily, but becomes a virus that has higher likelihood of making people very sick like H5N1. One of the pieces of good news is that, even if this virus were to become more deadly, it's likely that the vaccine that we currently have would be effective because the part of the virus that we make the vaccine against is distinct and independent from the part of the virus that determines whether it makes you very sick and is very deadly. If the H1N1 virus would mutate, the reaction or response would be the same as the current response.

The seasonal flu shot can be given on the same day as any other vaccine, including the shingles and the pneumococcal vaccine. If given on the same day, the shots should be given in different sites on the body. If desired, they can also be given at any interval before or after each other.

If you are moderately or severely ill, you might be advised to wait until you recover before getting the vaccine. If you have a mild cold or other illness, there is usually no need to wait.

Antibiotics have no effect on any type of influenza vaccine.

In general you should always talk to your doctor before getting a flu shot if you:

If you are sick with a fever when you go to get your flu shot, talk to your doctor or nurse about getting your shot at a later date. However, you can get a flu shot if you have a respiratory (breathing) illness without a fever; or if you have another mild illness

• Have ever had a severe allergic reaction to eggs;
• Have ever had a severe allergic reaction to a previous flu shot
• Have a history of Guillain-Barré syndrome (GBS)

If you have questions or concerns about your child getting the seasonal flu vaccine (or any) vaccine, talk with their doctor.

If you are sick with a fever when you go to get your flu shot, talk to your doctor or nurse about getting your shot at a later date. However, you can get a flu shot if you have a respiratory illness without a fever; or if you have another mild illness. The nasal-spray influenza (flu) vaccine can be given to people with minor illnesses, such as:

• diarrhea, or
• a mild upper respiratory tract infection, with or without a fever. 

If a person has nasal congestion, he or she should consider waiting to get the nasal-spray flu vaccine. He or she may want to wait until the nasal congestion is reduced. This is because the nasal congestion may limit the vaccine's ability to reach the nasal lining.  

Definitely talk to your doctor before getting a flu shot if you have:

• Any questions about whether you should get a flu shot;
• Ever had a severe allergic reaction to eggs;
• Ever had a severe allergic reaction to a previous flu shot; or
• A history of Guillain-Barré syndrome (GBS).  

Both the flu shot and the nasal-spray flu vaccine provide good protection against influenza when they match the influenza strains circulating that season.