Note: These FAQs only pertain to seasonal flu and not H1N1 pandemic flu. To understand the difference, see “Seasonal vs. H1N1 Flu Vaccine: What’s the Difference?”

• What is influenza vaccine?
• Who should get influenza vaccine and when?
• Who should not get the influenza vaccine?
• What are the side effects of the influenza vaccine?
• Is a thimerosal-free vaccine available?

What is influenza vaccine?

The standard flu vaccine is made from flu viruses that are grown on fertilized chicken eggs. The viruses are inactivated (killed) during the manufacturing process. The inactivated viruses are a source of proteins known as antigens that trigger a protective antibody response when injected into the arm or thigh muscle. Protective antibodies begin to appear one to two weeks after receiving a flu vaccination and last three to six months. This vaccine protects you against the three strains of seasonal flu that have been circulating in various forms over the last 30 years.

The flu vaccine must be given every year because the proteins on the surface of flu viruses, which the antibodies attack, tend to change from year to year. These antigens changes often require modification of the vaccine to match the most recent strains of flu. The 2009-2010 influenza vaccine contains antigens of the following strains: A/Brisbain/59/2007 (H1N1)-like, A/Brisbane/10/2007 (H3N2)-like and B/Brisbane/60/2008-like antigens.

A live, intra-nasal influenza vaccine was introduced in 2003. Its use is limited to healthy persons 2 to 49 years of age. The intranasal vaccine is generally as effective as the flu shot but may cause symptoms of a mild upper respiratory infection.
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Who should get influenza vaccine and when?

Patients who should receive a flu vaccine early in the flu season are:

1. High-risk patients:
   • Persons 50 years or older
     
   • Residents of nursing homes or long-term care facilities
     
   • Patients with chronic heart or lung conditions, including asthma, chronic obstructive pulmonary disease (COPD) and heart failure
     
   • Patients with chronic medical conditions such as diabetes, kidney problems, cancer, chemotherapy, long-term steroid treatment, sickle-cell disease or HIV infection
     
   • Women who will be pregnant during the flu season
     
   • Children receiving chronic aspirin therapy
     
   • Individuals with neuro-muscular conditions (such as individuals with multiple sclerosis, Alzheimer’s and spinal cord injuries)
2. All children 6 months to 18 years of age (both those with high-risk medical conditions and those who are healthy)
   
3. Household contacts and out-of-home caregivers of high-risk patients (including contacts of children 0 to 59 months)
   
4. Health care workers and first responders

For a complete list of patients who fall into a high-risk category and for more information about the flu, visit www.cdc.gov/flu.

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Who should not get the influenza vaccine?

The flu shot is fine for the vast majority of people, including breastfeeding women. However, several groups of people should take caution.

• Persons with a history of severe allergic reaction to eggs or the influenza vaccine should consult a physician before receiving influenza vaccine.
  
• Anyone ill with a fever should wait until the fever has resolved before being vaccinated.
  
• Children under 6 months of age should not get the flu shot because the vaccine is ineffective in this age group.
  
• Persons with a history of Guillain-Barre syndrome should consult their physicians before receiving the flu shot.
  
• The live, intranasal influenza vaccine is restricted to healthy, non-pregnant persons 2 to 49 years of age.

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What are the side effects of the influenza vaccine?

Influenza vaccine rarely causes serious adverse effects. The most common reaction to the flu shot is mild soreness at the site of injection, which is well tolerated. Flu-like symptoms, such as fever and muscle aches, occasionally occur six to 12 hours after receiving the flu shot and last one to two days. However, these symptoms are very rare with the split virus vaccine product used in the United States. The live, intranasal flu vaccine can cause symptoms of a head cold.

Guillain-Barre syndrome (GBS), an acute paralytic illness, was linked to the swine flu vaccine of 1976. Since 1976, studies have failed to show a similar association between subsequent flu vaccines and GBS. It is estimated that perhaps one to two excess cases of GBS per million persons vaccinated may be attributable to the flu shot. This extremely low incidence of GBS stands in contrast to the thousands of lives saved among high-risk persons by the flu shot.
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Is a thimerosal-free vaccine available?

Thimerosal, a preservative in the standard seasonal flu vaccine, is considered safe by the U.S. Centers for Disease Control and Prevention (CDC). Nonetheless, thimerosal, which contains a minute amount of mercury, has been phased out of routine childhood vaccines. A California state law effective July 1, 2006 mandates the use of influenza vaccine that has zero or trace amounts of thimerosal in two patient groups: children under 36 months of age and pregnant women. For patients not in these groups, thimerosal-free vaccine will be available at some PAMF locations.
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