The flu is caused by influenza viruses. The two main types that infect people, influenza A and influenza B, are genetically different. Influenza A can cause moderate to severe illness in all age groups and infects many species, including pigs, birds, and horses. Influenza B usually causes milder disease and primarily affects children. Both influenza A and influenza B strains cause seasonal outbreaks, typically during the fall and winter months in the U.S. Visit the CDC for this year’s flu season report.
Influenza A strains can also cause flu pandemics, like the 1918 flu and the swine flu in 2009. Pandemics happen when a new influenza A subtype, typically from animals, spreads in human populations that have not ‘seen’ the subtype before and have no immunity to it. Pandemic strains typically go on to become seasonal strains once the human population develops some immunity to them.
Influenza spreads through tiny airborne droplets created by coughing, sneezing, or talking, which can be inhaled or land on mucus membranes in the nose, mouth, or eyes. The flu can also be transmitted orally by kissing or by touching a surface contaminated with the virus and then touching your face. People with PI are equally at risk of contracting the flu as those without PI.
People with the flu are most contagious 1-2 days before symptoms appear and for 4-5 days after. The flu's incubation period is 1-4 days. While most people recover in a few days, some experience severe illness.
People with PI should discuss plans with their healthcare provider about dealing with the flu before the season begins, including:
In case of illness, those with PI should immediately contact their healthcare provider to get tested for influenza and start antiviral treatment, which is most effective within 48 hours of symptoms appearing. There are no at-home rapid flu tests, but physicians' offices or pharmacies can quickly diagnose influenza.
Antiviral medications for influenza work by preventing the virus from replicating and/or spreading. The same antiviral medicines that are effective for the general population are also effective for people with PI.
There are four antiviral drugs approved by the U.S. Food and Drug Administration (FDA) and recommended by the CDC to treat the flu. All four work on both influenza A and influenza B viruses. Three of the antivirals are also recommended for the prevention of influenza (i.e., prophylactic use).
Available as a pill or liquid suspension and is FDA-approved for the treatment of flu within 48 hours of symptoms in people 14 days and older. The CDC also recommends prophylactic use in those ages 3 months and older.
A powder that is administered using an inhaler device and is approved for early treatment of flu in people 7 years and older. It is also approved for prophylactic use in people 5 years and older. Note that it is not recommended for people with breathing problems like asthma or COPD or those with milk protein or lactose allergies.
A single-dose pill approved for the treatment of flu within 48 hours of symptoms and as post-exposure prophylaxis (i.e., after known exposure to the flu, but before symptoms begin) in people 5 years and older.
Given intravenously by a healthcare provider and is approved for early treatment of flu in people 2 years and older.
Antiviral treatment should be initiated in individuals with flu symptoms as soon as possible when there is known influenza activity in the community, even before they get tested for flu, especially for people at high risk of developing complications. For those with PI, antiviral medication can be given preventatively if a household member or other close contact becomes ill with the flu.
This page contains general medical and/or legal information that cannot be applied safely to any individual case. Medical and/or legal knowledge and practice can change rapidly. Therefore, this page should not be used as a substitute for professional medical and/or legal advice.
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