Each year the Food and Drug Administration (FDA) approves the vaccines set to be offered before the seasonal flu season begins, states the Mayo Clinic. The vaccine is available between September and mid-November, which is just before the flu season begins in late-fall to early winter. The seasonal flu vaccine changes each year to compensate for the rapid changes in the virus. In some cases, a special flu vaccine is created to immunize people against a new or different strain of the flu. For example, in the spring of 2009, a novel flu virus appeared. A special vaccine for H1N1, also called swine flu, was created and made available as quickly as possible.
Live Virus
A live virus flu vaccine refers to a solution made of weakened DNA from the seasonal flu strain. The purpose of administering a live virus is to give the body a chance to build antibodies against the infection. The antibodies are responsible for defending the body from the infection, and essentially killing off the virus. A live virus for the seasonal flu is administered via a nasal spray. A nurse or other qualified medical professional inserts a small nasal pump into one nostril at a time while blocking the opposite nostril with a finger. A quick squeeze to the bottle pushes a fine mist containing the vaccine into the nasal passages. The CDC recommends this type of vaccine only for health individuals between the ages of two and 49.
Inactive Virus
The flu shot contains the inactivated seasonal flu virus. The virus has essentially been killed, states the CDC but it is still capable of immunizing people. Just like the live virus, the inactive virus enters the body and causes antibodies to be formed to protect against future exposure to the flu. The injection is recommended for use in individuals older than six months, even those who have health issues, states the CDC.
Novel Flu Vaccines
The CDC reports that novel flu vaccines are typically created for injection administration. The H1N1 vaccine of 2009 was administered only in injection form when it was first created. When specific flu viruses become persistent, the CDC adds them to the seasonal flu vaccine. For example, the CDC reported in 2009 that the seasonal flu vaccine contained the influenza virus type A (H3N2), regular seasonal type A (H1N1) which is different from the 2009 novel H1N1, and one type B flu virus.
