FluMist is a live, "attenuated"--or weakened--virus vaccine administered as a nasal spray. The Food and Drug Administration has approved FluMist for use in healthy people between the ages of 2 and 49 who are not pregnant. Children under age 9 who have not been vaccinated for flu in the past require two doses.
Viruses in FluMist
FluMist is a trivalent vaccine, which means it actually contains three kinds of influenza viruses. For the 2010-2011 flu season, the viruses selected by the FDA include A/California/7/09 (H1N1)-like virus, A/Perth /16/2009 (H3N2)-like virus and B/Brisbane/60/2008-like virus.
Attenuation
The FDA reports that the viruses in FluMist differ from circulating influenza viruses in two ways. First, they are "cold-adapted" and "temperature sensitive," which means they exhibit minimal growth at human body temperature. Second, they do not produce the classic symptoms of influenza, such as fever, dry cough and muscle pain in the back and lower extremities.
Risk of Spread
According to the Centers for Disease Control and Prevention, the risk of spreading the viruses in FluMist is extremely low--about 0.6 to 2.4 percent for close contacts of vaccinated people. Contacts of people who are severely immunosuppressed, such as those who are undergoing bone marrow transplant, should not be immunized with FluMist. FluMist is safe for contacts of people with lesser degrees of immune system compromise, such as people with HIV, people who are taking corticosteroids and people with diabetes.
Effectiveness
FluMist may result in more robust immunity to flu since it mimics the natural history of influenza virus infections. The CDC reports that some studies show that FluMist is more effective than the flu shot; however, it is difficult to make comparisons because FluMist is not approved for use in many of the groups classified as high risk for flu-related complications.
Side Effects of FluMist
According to the FDA, side effects of FluMist include runny nose, nasal congestion, cough, chills, fatigue, sore throat and headache. Side effects are typically mild and short-lived compared to the flu.
Contraindications
Contraindications of FluMist include age younger than 2 or older than 49, pregnancy, chronic lung, heart or kidney disease, diabetes, immune system problems or use of immunosuppressive medications, history of wheezing, aspirin use, history of Guillain-Barre syndrome within six weeks of a previous flu vaccine or allergy to any component of FluMist. With the exception of the last two, these contraindications relate to the low risk that the viruses in FluMist could mutate back to the wild-type viruses that cause the flu.
