Swine flu--what scientists now call 2009 H1N1--represents a quadruple reassortment virus, a novel combination of four genes from flu viruses that infect birds, humans and pigs in Europe and Asia. The Centers for Disease Control and Prevention discovered the disease in April 2009, after the production for the 2009-2010 seasonal flu vaccine was already underway. A separate swine flu vaccine was produced for that season, but the Food and Drug Administration announced that the seasonal flu vaccine will provide protection against swine flu for the 2010-2011 and future seasons.
Availability
The FDA starts to release lots of flu vaccine in October of each year. Initially, the vaccine may be reserved for people at high risk of flu-related complications. For information about the availability of vaccine in a certain area, patients should contact their local public health department or consult the CDC website.
Priority Groups
The CDC classes some people--including people 50 years and up, children younger than 19, pregnant women, residents of long-term care facilities and people with chronic medical problems--as "priority groups" for the vaccine because such people face increased risk of flu-related complications. Individuals who live or work with someone at high risk of flu-related complications also fall into this group by virtue of association.
Indications
The FDA has approved the flu shot for anyone over the age of 6 months. The nasal spray vaccine is approved for healthy people between the ages of 2 and 49 years who are not pregnant.
Contraindications
People with severe hypersensitivity to eggs or other vaccine components and those who have previously experienced a life-threatening allergic reaction in response to a flu vaccine should not be vaccinated again.
Dosing
Children younger than 9 who have not been vaccinated against flu in the past should receive two doses of the vaccine, delivered at least four weeks apart. The flu shot dose for children 6 months to 3 years is 0.25 mL; for all others, the dose is 0.5 mL. The nasal spray vaccine is the same dose for everyone--0.2 mL.
Administration
The flu shot is injected into the muscle of the upper arm for adults and all children except infants, who receive the shot in the muscle of the thigh. The nasal spray vaccine is, as the name implies, administered as a spray in one of the nostrils.
Effectiveness
Swine flu is a new form of the flu virus and, as of June 2010, data on the effectiveness of the 2009-2010 single strain vaccine is still pending. According to the CDC, in years where the vaccine and circulating flu viruses are well-matched, the vaccine reduces the risk of flu by 70 to 90 percent in healthy adults. Even when the vaccine does not prevent a person from getting sick, it can still reduce the duration and severity of symptoms through a process the CDC calls "cross matching."
