Flu Vaccine (Influenza Immunization) FAQ's Answered

What is flu?

The flu (or common flu) is a viral infection that is spread from person to person in secretions of the nose and lungs, for example when sneezing. Medically it is referred to as influenza. Flu is a respiratory infection, that is, an infection that develops primarily in the lungs. Respiratory infections caused by other viruses often are called flu, but this is incorrect. Influenza usually causes higher fever, more malaise, and severe body aches. Although other viruses may cause these symptoms, they do so less commonly.

The flu is a common illness. Every year in the United States, on average:

• 5% to 20% of the population gets the flu,
  
  
• more than 200,000 people are hospitalized from flu complications, and



• about 36,000 people die from the flu.

Why vaccinate for the flu?

The flu is highly infectious and is a serious viral respiratory infection. 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 is the flu vaccine?

Flu vaccine is an inactivated vaccine, meaning that it contains killed influenza virus. The killed influenza virus is injected into muscles and stimulates the immune system to produce an immune response (antibodies) to the influenza virus. When the virus enters a person who has been vaccinated, the antibodies attack and kill the virus and prevent infection.

Each year, the influenza virus can change slightly, making the vaccine used in previous years ineffective. Each year, a new vaccine must be prepared that will be effective against the expected type of influenza virus. The trick 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. The viruses that are used to prepare flu vaccine are grown in eggs.

The vaccine is generally effective against the influenza virus within two weeks of the injection. 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.

Flu season can begin in October and last as late as May. October and November are considered the best times to receive the vaccination, but it is still effective when administered later.

Flu vaccination does not protect against infection caused by microbes other than the influenza virus.

Who should receive the flu vaccine?

While anyone who wishes to reduce their risk of getting the flu can be vaccinated, the U.S. Centers for Disease Control and Prevention (CDC) recommends that certain groups of people (who are at risk for serious complications from the flu) be vaccinated each year. When vaccine supplies are limited or delayed, the CDC makes recommendations for priority groups of people who should receive the vaccination. The CDC recommends vaccination for the following groups:

1. People at high risk for complications from the flu, including:

• people ages 65 and older,



• people who live in nursing homes and other long-term care facilities that house those with long-term illnesses,



• adults and children 6 months and older with chronic heart or lung conditions, including asthma,



• adults and children 6 months and older who needed regular medical care or were in a hospital during the previous year because of a metabolic disease (like diabetes), chronic kidney disease, or weakened immune system (including immune system problems caused by medicines or by infection with human immunodeficiency virus [HIV/AIDS]),



• children 6 months to 18 years of age who are on long-term aspirin therapy (children given aspirin while they have influenza are at risk of Reye syndrome),



• women who will be pregnant during the influenza season,



• all children 6 to 23 months of age, and



• people with any condition that can compromise respiratory function or the handling of respiratory secretions (that is, a condition that makes it hard to breathe or swallow, such as brain injury or disease, spinal cord injuries, seizure disorders, or other nerve or muscle disorders).

2. People 50 to 64 years of age. Almost one-third of people in this age group in the U.S. have one or more medical conditions that place them at increased risk for serious flu complications.

3. People who can transmit flu to others at high risk for complications .This means that all health-care workers, caregivers of children 6 to 23 months of age, close contacts of people 65 years and older, or any person in close contact with someone in a high-risk group (see above) should be vaccinated so that they do not spread the infection to a high-risk population.

How is the flu vaccine administered?

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 the injection is 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.

What side effects can occur with flu vaccination?

Side effects of the inactivated flu vaccine are not common. Side effects include soreness at the site of the injection, muscle aching, fever, and feeling unwell. Very rarely, serious allergic reactions have been reported.

Guillain-Barre syndrome (GBS) is an illness characterized by fever, nerve damage, and muscle weakness. In 1976, vaccination with the swine flu vaccine was associated with development of GBS. Studies have been done to evaluate if other flu vaccines were associated with GBS, with only one of the studies showing an association. That single study suggested that one person out of 1 million vaccinated persons may be at risk of GBS associated with the vaccine.

Who should not receive the flu vaccine?

Those who should avoid the flu vaccine include:

• people with a history of allergic reactions to eggs,



• those with a history of hypersensitivity to the vaccine,



• those with recent febrile (having fever) illness (although you can be vaccinated if you have a cold or other mild illness without fever), and



• subsequent vaccination should be avoided for people known to have developed the rare nerve disease Guillain-Barré syndrome (GBS, see above) within six weeks of a previous vaccination.

How effective is the flu vaccine?

The effectiveness of the flu vaccine is dependent upon the extent of the match between the virus strains used to prepare the vaccine and those viruses in actual circulation. The age and health status of the individual also play a role in determining the effectiveness of the vaccine. Research has shown that when there is a good match between the virus strains chosen for the vaccine and those in circulation, the vaccine prevents influenza illness in approximately 70%-90% of healthy adults under 65 years of age.

A study of children from 1 to 15 years of age showed that inactivated influenza vaccine was 77%-91% effective in preventing influenza respiratory illness. The effectiveness of the vaccine in preventing respiratory illness in people over 65 is somewhat lower. Among older people who reside in nursing homes, influenza vaccine is most effective in preventing severe illness, secondary complications, and deaths. The vaccine can be 50%-60% effective in preventing influenza-related hospitalization or pneumonia and 80% effective in preventing influenza-related death, although the effectiveness in preventing influenza respiratory illness can be as low as from 30%-40%.

What is the nasal spray flu vaccine?

A newer vaccine is available that is administered via a nasal spray. 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 viruses are weakened so that they do not cause severe flu symptoms. The nasal spray flu vaccine (LAIV) has been approved by the U.S. Food and Drug Administration (FDA) for use in nonpregnant healthy people between the ages of 5 and 49 years. In September 2007, the FDA also approved use of the nasal flu vaccine for healthy children 2-4 years old (24-59 months old) without a history of recurrent wheezing.

People at risk for serious complications from the flu (as described above) should not receive the nasal spray flu vaccine. In particular, certain groups are advised to receive the inactivated flu vaccine rather than the nasal spray vaccine, including:

• children younger than 5 years of age who have recurrent wheezing,



• people with chronic health problems, including heart and lung disease,



• pregnant women,



• people with suppressed immune function and those who care for or come into contact with those with a suppressed immune system,



• adults over age 50 or children 6 months to 2 years of age, and



• children or adolescents receiving aspirin therapy.

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 include runny nose, headache, sore throat, and cough. Children who receive the vaccine may also develop mild fever and muscle aches.