The Children's Hospital of Philadelphia reports that "influenza hospitalizes and kills more people in this country [the U.S.] than any other vaccine-preventable disease." Yearly estimates average nearly 200,000 people admitted to hospitals, and nearly 40,000 deaths.The Centers for Disease Control (CDC) describes a flu shot as an injection of "an inactivated vaccine (containing killed virus) that is given with a needle, usually in the arm."
The Science
The flu virus is an RNA enveloped virus that is made up of an RNA core surrounded by a viral pocket. Each virus has specific characteristics determined by the tiny spikes, called surface proteins, on the surface of the pocket. Viruses are classified by the year in which they were isolated (the current H1N1 has the date 2009 included in the official identification), the geographic region first infected (as in Hong Kong Flu), and the host (such as bird flu or swine flu). Each of these elements is critical in determining the ingredients for the vaccine. Scientists working at the World Health Organization (WHO), national health organizations and drug manufacturers collaborate to identify yearly influenza outbreaks.
Virus Identification and Shot Formulation
Influenza viruses are also classified by the flu subtype. Most modern strains are part of the general classification of Influenza-A. Subtypes of this group include HA and NA. More than 16 different HA subtypes and nine NA subtypes have been recorded, and they are found mainly in the bird population. Only a handful of subtypes create influenza symptoms in humans. Influenza-B viruses are less common and two subtypes have been identified. Identification of the virus must be done to create the flu vaccine.
Specific Shot Ingredients
Vaccines include either a live attenuated or inactivated vaccine. The body creates antibodies to counter the injected virus and protect the host against future infection. This dead virus, which is called the "antigen preparation," may include an inactivated whole virus, a split vaccine (containing only purified virus particles), or subunits (specific parts such as HA or NA subtypes). Scientists cannot accurately predict genetic changes and modifications, called "antigenic shift" or "drift," that the virus will undergo as it is transferred during the season. For this reason, most flu shots contain a combination of virus strains and at least two influenza A and one B virus strains. Occasionally, the drift is so dramatic that the initial vaccine is ineffective against the new influenza strain. This virus shift requires a new vaccine and also mandates that patients receive a second flu shot formulated for the modified virus. The Mayo Clinic reports that persons obtaining shots for the 2009-2010 season, for instance, receive two vaccines: one routine combination season shot and a second shot specifically formulated for H1N1-2009 (also known as the swine flu).
General Shot Ingredients
Other ingredients, including preservatives, are included in vaccine formulas to keep it safe from germs and fungi, and for ease of transportation and storage. Calcium chloride, sulfates, potassium and sodium phophates, egg protein, formaldehyde or formalin (remnants left from killing the live virus), gelatins, albumin, sodiums, and monosodium glutamate may be found in the vaccine. People with allergies to sulfates and eggs should consult a doctor before receiving a flu shot. Thimerosal, a mercury product, is also used as an inexpensive preservative, but preservative-free influenza vaccines are available for children under the age of 6. The CDC reports that only small amounts of this formula are available for use in people with allergies, pregnant women and young children.
