Patient information: Influenza prevention

INFLUENZA VACCINE OVERVIEW

The most effective way to prevent influenza is by getting the influenza vaccine (the flu shot) as well as using simple infection control measures such as hand washing. Antiviral medicines can also help prevent infection if you are exposed to the flu.

This article will discuss ways to prevent infection with influenza. The symptoms and treatment of influenza are discussed separately. (See "Patient information: Influenza symptoms and treatment".)

INFLUENZA VACCINE

Influenza vaccine can reduce the chance of becoming infected with the flu. People who get the influenza vaccine have a lower chance of illness and death from influenza compared to people who are not vaccinated. (See "Seasonal influenza vaccination in adults" and "Seasonal influenza vaccination in children" and "Prevention of pandemic H1N1 influenza ('swine influenza')".)

Timing — Because the influenza virus changes (or "mutates") slightly from year to year, you need a new influenza vaccine before each flu season.

Seasonal flu — Vaccination against the seasonal flu is recommended in October or November in the northern hemisphere. Vaccination in December or later is probably still effective. Flu season can begin as early as October and last until May. In addition, flu can occur at any time in the tropics; travelers to these areas need only to be vaccinated once per year.

H1N1 swine influenza — A vaccine that protects against the H1N1 swine flu became available in the United States in October 2009.

Effectiveness — People who are vaccinated form antibodies (proteins), which destroy the virus after the person is exposed. It generally takes about two weeks to make these antibodies. The vaccine can protect 50 to 80 percent of vaccinated people from getting the flu.

Injection versus nasal spray — The flu vaccine is available in two forms in the United States, as an injection and a nasal spray.

• The injection is approved for adults and children 6 months and older.
• The nasal spray is approved only for healthy children age 24 months and older and healthy adults up to 49 years.

Pregnant women and people who have a weakened immune system or who have chronic heart, lung, kidney, or metabolic disease should not get the nasal spray since it contains live virus. If you live with a person with a severely weakened immune system, you should not get the nasal spray (table 1).

Vaccine side effects — The most common side effect of the influenza vaccine is soreness at the injection site. Because the vaccine is prepared from viruses grown in eggs, people with a serious allergy to egg products should talk with their doctor or nurse before getting the vaccine. (See "Patient information: Food allergy treatment and avoidance".)

WHICH VACCINE DO I NEED?

Seasonal influenza vaccine — The season flu vaccine is recommended for people at risk for influenza-related complications, including:

• Adults age 50 or older
• Residents of nursing homes and other long-term care facilities
• Adults and children who have chronic lung or heart conditions, including children with asthma
• Adults and children with chronic diseases such as diabetes, kidney problems, or problems of the immune system, including HIV infection
• Children and teenagers age 6 months to 18 years who are taking long-term aspirin therapy and might be at risk for Reye syndrome
• Women who will be pregnant during the influenza season
• Adults and children who might transmit influenza to high-risk individuals. This includes health care workers, workers at nursing homes, providers of home care, and household members of people in high-risk groups

H1N1 swine influenza vaccine — Experts recommend that people at the highest risk of complications of the H1N1 swine flu be vaccinated first, including [1]:

• Pregnant women
• Adults and children who live or care for infants who are younger than 6 months old (parents, siblings, daycare providers)
• Healthcare workers
• Children and adults who are 6 months to 24 years old
• Adults age 25 to 64 who have health conditions that increase the risk of developing complications of influenza

Once these groups are vaccinated, everyone who is 25 to 64 years old should be vaccinated, followed by people who are 65 years and older.

ANTIVIRAL DRUGS

Antiviral drugs can help to reduce a person's chances of developing the flu after being exposed. These drugs can also be used by a limited number of people who are at risk for developing complications from the flu who cannot receive the flu vaccine. The drugs are also used to limit outbreaks of influenza.

Oseltamivir, zanamivir, rimantadine, and amantadine are antiviral drugs approved for prevention of influenza (table 2). The choice of drug depends on the strains of influenza circulating in the community. The length of treatment with an antiviral drug depends upon how the person was exposed to influenza (directly to someone with the infection versus living in a community where there is an outbreak). (See "Prevention of seasonal influenza in adults" and "Antiviral drugs for the prevention and treatment of influenza in children" and "Prevention of pandemic H1N1 influenza ('swine influenza')".)

INFECTION CONTROL

Infection control measures can help to prevent the spread of influenza. Infection control is most commonly practiced in healthcare settings, but is useful in the community as well. Frequent hand washing with soap and water or alcohol-based hand rubs can be effective.

Because influenza is spread by contact with infected respiratory secretions (coughing, sneezing), people with influenza should limit face-to-face contact with uninfected family and friends. The mouth and nose should be covered while coughing or sneezing, and tissues should be disposed of immediately. Sneezing/coughing into the sleeve of your clothing (at the inner elbow) is another means of containing sprays of saliva and secretions and will not contaminate your hands.

WHERE TO GET MORE INFORMATION

Your healthcare provider is the best source of information for questions and concerns related to your medical problem. Because no two people are exactly alike and recommendations can vary from one person to another, it is important to seek guidance from a provider who is familiar with your individual situation.

This discussion will be updated as needed every four months on our web site (www.uptodate.com/patients). Additional topics as well as selected discussions written for healthcare professionals are also available for those who would like more detailed information.

Some of the most pertinent include:

Patient Level Information:
Patient information: Influenza symptoms and treatment
Patient information: Food allergy treatment and avoidance

Professional Level Information:
Avian influenza vaccines
Clinical manifestations and diagnosis of seasonal influenza in adults
Epidemiology of influenza
Pharmacology of antiviral drugs for influenza
Prevention of seasonal influenza in adults
Seasonal influenza vaccination in adults
Treatment of seasonal influenza in adults
Seasonal influenza vaccination in children
Prevention of pandemic H1N1 influenza ('swine influenza')
Antiviral drugs for the prevention and treatment of influenza in children

A number of web sites have information about medical problems and treatments, although it can be difficult to know which sites are reputable. Information provided by the National Institutes of Health, national medical societies and some other well-established organizations are often reliable sources of information, although the frequency with which they are updated is variable.

• National Library of Medicine

      (www.nlm.nih.gov/medlineplus/flu.html)

• National Institute of Allergy and Infectious Diseases

      (www3.niaid.nih.gov/topics/Flu/)

• Centers for Disease Control and Prevention (CDC)

      (www.cdc.gov/h1n1flu/)

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