Influenza prevention

Author
Patricia L Hibberd, MD, PhD Section Editor
Martin S Hirsch, MD Deputy Editor
Leah K Moynihan, RNC, MSN
Anna R Thorner, MD

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 medications can also help prevent infection after exposure, but they are generally reserved for people who are at risk for complications of influenza.

This topic 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 is effective in reducing the chance of becoming infected with the flu. Giving the vaccine to children who are in school or daycare appears to decrease the risk of influenza in unvaccinated children and adults of all ages. People who get the influenza vaccine have a lower chance of illness and death from influenza compared to people who are not vaccinated. (See “Influenza vaccination in adults” and see “Influenza vaccination in children” and see “Prevention of H1N1 influenza A (swine influenza)”)

Timing — Vaccination is usually recommend in October or November. In years when there was a significant shortage of vaccine, the recommendation was to delay vaccination. Vaccination in December or later is still effective in most situations. 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.

Because the influenza virus changes (or “mutates”) slightly from year to year, a new vaccine must be produced and given before each flu season. Immunization is needed once per year, even if the previous year’s vaccine contained one or more of the current years’ viruses because a person’s response to the vaccine (immunity) declines during the year following vaccination.

Effectiveness — Although there is concern that a yearly vaccine might become less effective over time, a recent study found an increase in protective immunity over a three-year period in a group of healthy elderly and young patients who were vaccinated yearly [1] .

The influenza vaccine requires approximately nine months to be manufactured. As a result, each year’s vaccine is based on the previous year’s flu virus and viral strains known to be circulating in other parts of the world. The vaccine’s effectiveness for the current year’s flu, therefore, depends upon how well scientists are able to predict which strains will cause infection in a given year.

Patients who receive vaccine form antibodies (proteins), which destroy the virus after the person is exposed; it generally takes about two weeks to make these antibodies. If the circulating virus and strains used for the vaccine match closely, the vaccine can protect 50 to 80 percent of vaccinated individuals from getting the flu.

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

The intramuscular (IM) injection is approved for adults and children 6 months and older.
The intranasal spray is approved only for healthy children age 24 months and older and healthy adults up to 49 years.
People who have a weakened immune system or who have chronic heart, lung, kidney, or metabolic disease should not use the intranasal spray since it contains live virus. Household contacts of those who have severely weakened immune systems should also not receive the intranasal spray (show table 1).

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

Adults age 50 or older
Residents of LTCFs
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 LTCFs, providers of home care, and household members of people in high-risk groups
Vaccine safety — Because the intramuscular influenza vaccine does not contain live virus, it can be administered safely to people with weakened immune systems. It does not appear to worsen chronic neurologic diseases such as multiple sclerosis. In previous years, a slightly increased risk of Guillain-Barré syndrome (a neurologic disease) was associated with the flu vaccine. Because of this, the vaccine is generally not given to individuals who developed Guillain-Barré syndrome after a previous influenza immunization.

Flu vaccines are generally well tolerated. They do not cause the flu or flu symptoms. The most common side effect is soreness at the injection site. Because the vaccine is prepared from viruses grown in eggs, patients with serious allergy to egg products should talk with their healthcare provider before receiving the vaccine. (See “Patient information: Food allergy treatment and avoidance”).

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 (show 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 “Antiviral drugs for the prevention of influenza in adults” and see “Antiviral drugs for the prevention and treatment of influenza in children” and see “Prevention of H1N1 influenza A (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 one’s clothing (at the inner elbow) is another means of containing sprays of saliva and secretions and will not contaminate the 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.

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/healthtopics.html)

National Institute of Allergy and Infectious Diseases
(www.niaid.nih.gov/)

Centers for Disease Control and Prevention (CDC)
Toll-free: (800) 311-3435
(www.cdc.gov/epo/mmwr/mmwr.html)

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REFERENCES

1 de Bruijn, IA, Remarque, EJ, Jol-van der Zijde, CM, et al. Quality and quantity of the humoral immune response in healthy elderly and young subjects after annually repeated influenza vaccination. J Infect Dis 1999; 179:31.
2 Fiore, AE, Shay, DK, Broder, K, et al. Prevention and control of influenza. Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2008. MMWR Recomm Rep 2008; 57:1.
3 Jefferson, TO, Rivetti, D, Di Pietrantonj, C, et al. Vaccines for preventing influenza in healthy adults. Cochrane Database Syst Rev 2007; :CD001269.

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