There are two forms of this vaccine; the injectable form and the nasal spray. The injectable form contains heat-killed virus and comes in single dose vials and multiple dose vials. It is approved for use in healthy people 6 months of age and older. Children between the ages of 6 months and 9 years should receive two doses of the vaccine about a month apart. Because the seal on the multiple dose vial will be penetrated several times in order to withdraw doses of vaccine, the antiseptic and antifungal compound Thimerasol has been added as a preservative. Thimerasol contains nearly 50% mercury by weight and its presence in certain vaccines is the subject of growing concern because of its toxic potential. Single-dose vials of the vaccine are reported not to contain Thimerasol and this should be confirmed beforehand by asking your physician. If you decide to be vaccinated by injection and are concerned about mercury, you should request vaccine that does not contain Thimerasol.
The nasal spray contains live, weakened virus, which is temperature-sensitive. It is approved for use in healthy people between the ages of 2 and 49 but should not be given to pregnant women. The vaccine is contained in single-dose spray syringes and does not contain Thimerasol. Children between the ages of 2 and 9 will need two doses of this vaccine separated by about a month. A recipient of this live but weakened virus will not get the flu but for three weeks afterwards they should not be close to anyone whose immune system is seriously compromised by illness or by treatment such as chemotherapy. For more information on FluMist nasal spray vaccines, please refer to the article written by Dr. Iannelli (1).
The following people should not receive flu vaccine (2):
a) Those who have a severe allergy to hens’ eggs.
b) Individuals who have previously had a severe reaction to a flu vaccination.
c) People who developed Guillain-Barré syndrome (GBS) within 6 weeks of getting an influenza vaccine previously.
d) Children younger than 6 months of age.
e) People who have a moderate-to-severe illness with a fever. They should consult their physician and wait until they are well before getting vaccinated.
References
1) http://pediatrics.about.com/cs/immunizations/a/new_flu_vaccine.htm
2) Centers for Disease Control and Prevention (CDC) (2009) http://www.cdc.gov/h1n1flu/vaccination/vaccine_keyfacts.htm
© Christopher J. Jones, M.Sc., Ph.D.
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