History of the Vaccine

Influenza vaccines have been used since 1945. Each year, the vaccines contain three virus strains that are expected to affect the United States in the upcoming winter.

Until recently, all available influenza vaccines were trivalent inactivated (killed) virus vaccines (TIV). In spite of common belief, inactivated vaccines cannot cause influenza. In June of 2003, a live, attenuated, cold adapted, temperature sensitive, trivalent influenza virus vaccine (LAIV) was licensed in the United States. The temperature sensitive type A and B strains of influenza virus contained in LAIV replicate (multiply) in the nasal passages but not in the lower respiratory tract.

TIV came in whole-virus and split-virus forms prior to 2001; however, because of fewer side effects, including fever and reactions at the injection site, only split-virus vaccines are currently available in the U.S. Due to the change in the types of virus circulating each year, some of the components of the influenza vaccine must be changed as well.

Who should receive the TIV each year?

People (including children over six months of age) at increased risk of developing complications from influenza, including those who:

• Are children ages 6 to 23 months of age
• Are 50 years old or older (especially those 65 and older)
• Live in nursing homes or other long-term care facilities
• Have long-term disorders of the lungs, heart, or circulation (including asthma or cystic fibrosis)
• Have metabolic diseases (including diabetes)
• Have kidney disorders
• Have blood disorders (including anemia or sickle cell disease)
• Have weakened immune systems (including immunosuppression caused by medications, malignancies, organ transplant, or HIV infection)
• Are children who receive long-term aspirin therapy (and therefore have a higher chance of developing Reye syndrome if infected with influenza)
• Are women who will be pregnant during the influenza season (November to April)
• People who can transmit influenza viruses to those at high risk for complications, including:
  • All health care personnel.
  • Children who are members of households with high-risk persons. 

In addition, an influenza vaccine is encouraged for healthy people six months of age or older, who:

• Plan to travel to foreign countries and areas where flu outbreaks may be occurring, such as the Tropics and the Southern Hemisphere from April through September
• Travel as a part of large organized tourist groups that may include persons from areas of the world where flu viruses are circulating
• Attend school or college and reside in dormitories, or reside in institutional settings
• Wish to reduce their risk of becoming ill with influenza

Women who are breastfeeding may receive the vaccine. TIV does not affect the safety of mothers who are breastfeeding or the safety of their infants. It is not known if LAIV is excreted in human milk, therefore, caution is recommended.

Who should not receive influenza vaccine:

• Infants younger than six months of age
• Children younger than four years of age should not receive Fluvirin® (Chiron Corp.) because it has not been proven effective for them.
• Children younger than five years of age and adults over 49 years of age should not receive LAIV because safe use in these age groups has not been established.
• LAIV should not be given to children and adolescents (5-17 years of age) receiving aspirin or aspirin-containing medications, because of the complications associated with aspirin and wild-type influenza infection in this age group.
• People with a history of asthma or other reactive airway diseases should not be given LAIV because the safety of LAIV in people with a history of these problems has not been established.
• People with chronic underlying medical conditions that may predispose them to severe influenza infections should also not be given LAIV. For these people, TIV is indicated.
• LAIV should not be given to pregnant women.
• LAIV should not be given to people with a history of Guillain-Barre syndrome.
• LAIV should not be given concurrently with other live-virus vaccines. 
• People who have had an anaphylactic reaction (allergic reactions that cause difficulty breathing, which is often followed by shock) to eggs, egg products, or other components of the flu vaccine. There are antiviral agents which doctors can prescribe as an alternative for preventing influenza in such people.
• People with acute serious illness with fever
• People who are moderately or severely ill should consult with their physician before receiving any vaccine
• Under no circumstances should LAIV be given by injection.