Influenza Virus Fact Sheet

The influenza virus is responsible for the respiratory illness known as influenza or “flu” which infects cells within the nose, throat and lungs. The influenza virus is part of a family of RNA viruses known as the orthomyxoviridae, and there are three different types of this virus known as A, B and C. All three types can infect humans, but only types A and B are known to cause seasonal epidemics.


The influenza virus is most commonly spread person to person by droplets made when people cough, sneeze or talk. These droplets can find their way to the mouth or nose of people who are nearby or possibly be inhaled into the lungs. Infection can also occur by a person touching a surface or object that contains the virus and then touching his/her own mouth or nose.

The influenza virus is highly contagious and can spread to others up to six feet away. An infected person can even infect others one day before any sign of symptoms and up to seven days after becoming sick. Children infected with the influenza virus may pass on the virus seven days or longer after the initial infection.


The symptoms of influenza can cause mild to severe illness and at times, can lead to death. The following symptoms usually come on suddenly and all or some of the symptoms may be present. Symptoms include fever, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue, vomiting and diarrhea. Most people are able to recover from influenza in a few days or up to two weeks depending on the person’s health.

Other health complications can make an influenza infection very serious for example people with asthma may experience asthma attacks while they have the flu. Also pneumonia, bronchitis and sinus and ear infections are all examples of complications from the flu.


The best way to prevent the flu is by getting vaccinated each year. Everyone that is six months of age or older is recommended to get vaccinated against the flu each year. People who are at a higher risk for having additional health complications as a result of influenza include children who are less than five years of age, pregnant women, people with certain medical conditions like asthma, diabetes (type 1 and 2), heart and lung disease and people 65 years and older.

Other prevention methods include washing hands frequently with soap and water or using an alcohol based hand rub. Try to avoid close contact with people who are sick and try to stay home when you are ill. Also try not to share daily items with those who are sick, such as linens, eating utensils and dishes.


The Centers for Disease Control (CDC) recommends that receiving the seasonal flu vaccine each year is the first and most important step against the influenza virus. If you do happen to fall ill due to the influenza virus, the best thing to do is to stay home and avoid contact with other people, except to get medical care. Most people with the flu will have mild illness and do not need to receive medical care or antiviral drugs. People that are at high risk of serious illness should contact a health professional. Antiviral drugs can be prescribed by a health care professional and are used for prevention or treatment of the influenza viruses.

Influenza Vaccine

The influenza viruses are constantly changing, which is one of the reasons why a yearly flu vaccine is recommended. Every year a new influenza vaccine is developed with three different strains of the influenza virus. Researchers at the CDC try to predict which strains will be the most common for the upcoming flu season and create a vaccine against those viruses. They adapt the vaccine based on how well the previous manufactured vaccine reacts to the current viruses and any new virus types. The virus information is then presented to an advisory committee of the U.S. Food and Drug Administration (FDA) and World Health Organization (WHO), which then decide which three viruses, two subtypes of influenza A viruses and one influenza B virus, will go into the vaccines for upcoming flu season. Influenza type C causes only mild illness in humans and does not cause epidemics or pandemics and therefore is not present in the influenza vaccine.

The influenza vaccine is available via a needle or nasal spray. The “flu shot” contains an inactivated or killed virus and is usually given to people in the arm. The nasal spray vaccine version is made with live but weakened viruses. Both types of the vaccine do not cause influenza sickness.

Another reason that a yearly influenza vaccine update is recommended is because a person’s immune protection from the vaccination declines over time. The decline in a person’s immune protection against the influenza virus may be influenced by several factors including a person’s age, the antigen used in the vaccine, and the person’s overall health (such as any immune complications). This decline in defense may leave some people more susceptible to the virus and can pose a threat one year after the initial vaccination. For the best overall protection against the influenza viruses, annual vaccination is recommended.