Why vaccinate for the flu?
The flu is highly infectious and is a potentially serious viral respiratory infection that can even be life-threatening. Whereas with other viral respiratory infections the symptoms usually are mild and most people can continue working or going to school while ill, with the flu, the symptoms are severe and prolonged and cause individuals to miss days of work or school. The infection stresses the body. In addition, superinfections may occur. Superinfections are bacterial infections that occur on top of a respiratory infection. Bacterial respiratory infections also are a serious type of infection, and the simultaneous viral and bacterial infection can overwhelm the function of the lungs and the body. Among the elderly and the very young, it can cause death. Because of its infectiousness, morbidity (severity of symptoms and time lost from work or school), and the potential for death, it is important to prevent the flu by vaccination. Although there are medications to treat the flu, they are expensive, not as effective as vaccination, and need to be started within 24-48 hours of the start of symptoms.
What are the different types of flu vaccines?
Flu vaccines are routinely available for seasonal influenza. Pandemic vaccines may also be developed for specific strains of the flu virus that are causing widespread disease, such as occurred with the H1N1 virus in 2009.
Two types of seasonal flu vaccines have been used, those using killed virus and nasal spray vaccines that contain live but weakened virus.
Each year, composition of the influenza viruses change, making the vaccine used in previous years ineffective. Each year, a new vaccine must be prepared that will be effective against the types of influenza virus that are expected to circulate in the upcoming flu season. These are known as seasonal flu vaccines. The reason for the differences in circulating strains of the flu virus is that the virus can mutate (or change its structure) rapidly, leading to new subtypes of the virus. The key is to be able to predict which influenza viruses are going to cause infection and to prepare a vaccine against those viruses. Usually, scientists can predict accurately which types of influenza virus will cause infections and prepare an appropriate vaccine. Typically, the viruses that are used to prepare flu vaccine are grown in eggs, but a newer, egg-free version of the vaccine has been developed. In 2017, updated guidelines from the Influenza Vaccine and Egg Allergy Practice Parameter Workgroup commissioned by the Joint Task Force on Practice Parameters (JTFPP) stated that the risk is so small that even asking patients about egg allergy is no longer necessary. Flu vaccines can be safely administered to people who are allergic to eggs.
The vaccine is generally effective against the influenza virus within two weeks of administration. The vaccine is only effective against the strains of the virus that match the vaccine. These strains vary from flu season to flu season each year. This is the reason that revaccination is required annually with the vaccine that matches the strains of influenza that are currently prevalent.
The injection ("flu shot") vaccine
Flu vaccine is an inactivated vaccine, meaning that it contains killed influenza virus. The killed influenza virus is injected into muscles or skin and stimulates the immune system to produce an immune response (antibodies) to the influenza virus.
The inactivated flu vaccine is administered as a single dose of 0.5 mL of liquid injected through the skin into muscle (intramuscular or IM). Typically, health care professionals inject the flu vaccine into the deltoid muscle at the side of the arm, using alcohol rubbed over the skin for sterilization. The vaccine is given annually, each fall. Side effects of the inactivated flu vaccine are not common.
Two types of vaccines are available: a trivalent vaccine that targets three strains of flu virus, as well as a quadrivalent vaccine that targets four strains. Both the trivalent and quadrivalent vaccines are available as an intramuscular injection. The intradermal vaccine is a quadrivalent vaccine. Standard vaccines are grown in eggs, but a newer vaccine grown in cell culture without eggs has been produced. This egg-free vaccine is a trivalent vaccine and is approved for people 18 years of age and older. For people who are 18-64 years old, a jet injector (that uses a strong stream of fluid to penetrate the skin rather than a needle) can be used for administration of one particular trivalent flu vaccine (Afluria). A preparation first introduced in the 2011-2012 flu season is an intradermal vaccine that is injected into the skin rather than into the muscle. The intradermal vaccine is approved for people 18-64 years of age.
The U.S. CDC recommends the use of injectable influenza vaccines (either trivalent or quadrivalent, including inactivated influenza vaccines and recombinant influenza vaccines) for 2017-2018. The nasal spray flu vaccine (live attenuated influenza vaccine or LAIV) should not be used during 2017-2018.
The nasal-spray vaccine
The nasal-spray flu vaccine (sometimes called LAIV for live attenuated influenza vaccine, brand name FluMist) was first licensed in 2003. It is directed against the same strains of virus as the flu shot but differs in that it contains weakened live influenza viruses instead of killed viruses and is administered by nasal spray instead of injection. The vaccine is termed an attenuated vaccine because the vaccine viruses are weakened so that they themselves do not cause severe flu symptoms. The nasal spray flu vaccine is not recommended for the 2017-2018 flu season.
The live viruses in the nasal-spray vaccine are weakened so that they do not cause severe symptoms. However, mild symptoms can occur as a side effect of the vaccination. Side effects of the nasal-spray flu vaccine can included runny nose, headache, sore throat, and cough. Children who receive the vaccine may also develop mild fever and muscle aches.