Course Price  $10.00 Contact Hours  1 Instructions   Study the course, then take the test. You can also print the course and test questions and return later to take the test.

Quicklinks Print this course Take the test How to take a course

Influenza Update

Persis Mary Hamilton, RN, CNS, MS, EdD

Wild Iris Medical Education is an approved provider (#PA-54) of continuing nursing education by the Washington State Nurses Association, an accredited approver by the American Nurses Credentialing Center's Commission on Accreditation. Our courses fulfill continuing nursing education requirements in all 50 states.
Wild Iris Medical Education (CBRN Provider #12300) is approved as a provider of continuing education for RNs, LVNs, and respiratory therapists by the California Board of Registered Nursing.
Nurse practitioners may apply these contact hours to pharmacy continuing education and prescriptive authorization.

The information in this course is taken primarily from the Centers for Disease Control and Prevention, Prevention and Control of Influenza, Recommendations of the Advisory Committee on Immunization Practices (ACIP; 2008–2009 Influenza Vaccine Updates).

THE IMPACT OF INFLUENZA

Influenza (the "flu") is a highly contagious infection of the respiratory tract caused by a myxovirus and transmitted by airborne droplets. The incubation period is brief and the onset sudden, with chills, fever, and general malaise. Symptoms include sore throat, cough, fever, muscle pain, and weakness. The disease occurs in isolated cases, epidemics, and pandemics. Treatment is symptomatic and usually involves bed rest, aspirin, and fluids. Fever and malaise distinguish influenza from the common cold. It can cause mild to severe illness and, in some instances, lead to death. Most healthy people recover within 3 to 10 days, but bacterial pneumonia may occur among the very young, the elderly, and those with chronic pulmonary disease.

Flu usually starts suddenly and may include these symptoms:

• Fever (usually high)
• Headache
• Extreme fatigue
• Cough and sneezing
• Sore throat (rhinitis)
• Runny or stuffy nose
• Body aches
• Diarrhea and vomiting (more common in children)
• Irritated, watery eyes

These indications of illness are referred to as "flu-like symptoms." Other illnesses, including the common cold, can have similar symptoms.

Human influenza is transmitted primarily via large, virus-laden droplets that are generated when infected individuals cough or sneeze. These large droplets may be deposited directly onto the mucosal surfaces of the upper respiratory tract of susceptible individuals who are near the droplet source. Transmission may also occur through direct or indirect contact with infectious respiratory secretions. It is possible for a person to be actively transmitting the flu virus without having any signs and symptoms of the disease.

Epidemics of influenza typically occur during the winter months. Although the incidence of influenza can vary widely, the Center for Disease Control reports that every year in the United States there are more than 200,000 hospitalizations and approximately 36,000 deaths directly associated with influenza.

Influenza viruses cause disease among all age groups. Rates of infection are highest among children, but rates of serious illness and death are highest among people over 65 years of age and people of any age who have medical conditions that place them at increased risk for complications from influenza.

Influenza vaccination is the primary method for preventing influenza and its severe complications. Such vaccination helps reduce influenza-related respiratory illness, complications, physician visits, hospitalization, and death among people at high risk.

While antiviral drugs have been developed to reduce the symptoms and complications of the disease, different strains of influenza virus have different degrees of resistance to the drugs. As a result the effectiveness of these drugs is limited. For this reason, vaccination is a far more effective way to control influenza.

THE BIOLOGY OF INFLUENZA

The influenza virus is an RNA virus of the family Orthomyxoviridae (the influenza viruses). Two types of influenza viruses cause epidemic human disease: Influenza A and B.

Influenza A viruses are categorized into subtypes on the basis of two surface antigens: hemagglutinin (H) and neuraminidase (N). Antigens are substances the body recognizes as foreign; as a result, the body reacts with what is called an immune response. Influenza B viruses do not have identified subtype categories.

The influenza A and B viruses are further separated into groups on the basis of antigenic (immune response) characteristics. New influenza virus variants result from frequent antigenic drift.

Antigenic drift is the tendency of a virus to alter its genetic makeup. Thus, new antibodies must be produced to combat the altered virus. When this occurs, a new vaccine is required. As a consequence, people need repeated vaccinations to protect them from the altered viruses. Influenza B viruses undergo antigenic drift less rapidly than influenza A viruses.

A person's immunity to the surface antigens, including hemagglutinin, reduces the likelihood of infection and the severity of the disease if infection occurs. An antibody against one influenza virus type or subtype confers little or no protection against another. Furthermore, antibodies to one antigenic variant of influenza virus may not protect against a new antigenic variant of the same type or subtype. Frequent development of antigenic variants through antigenic drift is the virologic basis for seasonal epidemics and the reason that each year the new strains must be included in the latest influenza vaccine.

SIGNS AND SYMPTOMS

Uncomplicated influenza illness is characterized by the abrupt onset of constitutional and respiratory signs and symptoms such as fever, muscle pain, headache, malaise, nonproductive cough, sore throat, and rhinitis. Among children, nausea, vomiting, and otitis media are commonly reported with influenza illness. On the basis of symptoms alone, respiratory illness caused by influenza is difficult to distinguish from illness caused by other respiratory pathogens.

Among certain individuals, influenza can exacerbate underlying medical conditions such as pulmonary or cardiac disease, lead to secondary bacterial pneumonia or primary influenza viral pneumonia, or occur as part of a co-infection with other viral or bacterial pathogens.

Young children with influenza infection can have initial high fevers that mimic bacterial sepsis. Influenza has also been associated with encephalopathy, transverse myelitis, myositis, myocarditis, and pericarditis. Children who are medicated with aspirin have a 35% increased risk of developing Reyes syndrome, a serious, life-threatening fatty infiltration of internal organs and encephalopathy. For this reason, aspirin should not be administered to children under 18 years of age.

The incubation period for influenza is 1 to 3 days. Adults typically are infectious from the day before symptoms begin through approximately 5 days after onset of illness. Children can be infectious for more than ten days, and severely immunocompromised individuals for weeks or months.

THE RISKS FOR COMPLICATIONS

The risks for complications, hospitalizations, and deaths from influenza are higher among adults over the age of 65, young children, and individuals of any age with certain underlying health conditions. Risks are lower among healthy older children and younger adults. Estimated rates of influenza-associated hospitalizations vary substantially by age group.

INFLUENZA VACCINES

Two types of vaccine are available in the United States: Trivalent inactivated vaccine (TIV) and live attenuated influenza vaccine (LAIV). TIV contains dead virus. LAIV contains attenuated (or weakened) viruses. The weakened strains of LAIV do not usually cause illness because they have lost virulence. However, they may possibly reproduce and cause disease, especially in persons with weakened immune systems. Both types of vaccines reduce the risk for virus infection and its complications.

Comparing TIV and LAIV

Administered annually to provide optimal protection, both TIV and LAIV provide effective prevention against influenza. Both vaccines contain strains of influenza viruses antigenically equivalent to the annually recommended strains: one influenza A(H3N2) virus, one A(H1N1) virus, and one B virus. Each year, based upon global surveillance for influenza viruses and the emergence and spread of new strains, one or more virus strains might be changed. Viruses for both vaccines are grown in eggs. The vaccines do differ in several aspects.

TIV contains killed viruses, and thus cannot produce signs or symptoms of influenza virus infection. TIV is approved for use among individuals over 6 months of age, including both those who are healthy and those with chronic medical conditions by the Food and Drug Administration (FDA). The vaccine is administered intramuscularly.

LAIV contains live, attenuated viruses and has a potential to produce mild symptoms related to influenza virus infection. It is FDA-approved only for use among healthy individuals ages 2 to 49 years of age and is administered intranasally by sprayer.

Effectiveness of TIV

Over time, the effectiveness of TIV has been amply demonstrated. Multiples studies have established that high post-vaccination hemagglutination inhibition antibody titers develop in the majority of vaccinated children and young adults. These antibodies are protective against illness caused by strains that are antigenically similar to those strains of the same type or subtype included in the vaccine.

Dosage recommendations vary according to age group. Among previously unvaccinated children aged 6 months up to 9 years, two doses of inactivated vaccine administered >1 month apart are recommended for eliciting satisfactory antibody responses. If possible, the second dose should be administered before the onset of influenza season.

If a child aged 6 months up to 9 years receiving influenza vaccine for the first time does not receive a second dose of vaccine within the same season, only one dose of vaccine should be administered the following season; two doses are not required at that time. The CDC's Advisory Committee on Immunization Practices (ACIP) does not recommend that a child receiving influenza vaccine for the first time be administered the first dose of vaccine in the spring as a priming dose for the following season.

Among adults, studies have indicated limited or no improvement in antibody response when a second dose is administered during the same season. Even when the current influenza vaccine contains one or more antigens administered in previous years, annual vaccination is necessary because immunity declines during the year after vaccination. Vaccine prepared for a previous influenza season should not be administered to provide protection for the current season.

Children under 6 months of age usually acquire protective levels of anti-influenza antibody against specific influenza virus strains after vaccination, although the antibody response among children at high risk for complications might be lower than among healthy children. Two studies have documented that TIV vaccine decreases the incidence of influenza-associated otitis media among young children by approximately 30%.

Effectiveness of LAIV

The immunity provided by LAIV has been assessed in multiple studies. The LAIV virus strains replicate primarily in the cells of the nasopharynx. Its protective mechanisms are not completely understood but they appear to involve antibodies in both serum and nasal secretions. In studies, LAIV demonstrated up to 92% efficacy in preventing influenza in healthy children. It was also associated with reductions in otitis media (ear infections).

In a controlled study of both LAIV and TIV among 92 healthy adults, the overall efficacy against all three influenza strains combined was between 85% and 71%. The difference between the two vaccines was not statistically significant.

Multiple studies have demonstrated the ability of LAIV to stimulate an immune response (immunogenicity). LAIV is an option for vaccination of healthy, nonpregnant individuals aged 2 to 49 years who want to avoid influenza, and those who might be in close contact with others at high risk for severe complications, including healthcare workers.

LAIV can be administered to clients with minor acute illnesses (eg, diarrhea or mild upper respiratory tract infection with or without fever). However, if clinical judgment indicates nasal congestion is present that might impede delivery of the vaccine to the nasopharyngeal mucosa, deferral of administration should be considered until resolution of the illness.

The following populations should not be vaccinated with LAIV:

• People under 2 years or over 50 years of age
• People with asthma, reactive airways disease, or other chronic disorders of the pulmonary or cardiovascular systems; people with other underlying medical conditions, including such metabolic diseases as diabetes, renal dysfunction, and hemoglobinopathies; or people with known or suspected immunodeficiency diseases or who are receiving immunosuppressive therapies
• Children or adolescents receiving aspirin or other salicylates (because of the association of Reye syndrome with wild-type influenza virus infection);
• People with a history of group-B strep (GBS)
• Pregnant women
• People with a history of hypersensitivity, including anaphylaxis, to any of the components of LAIV or to eggs

The safety and effectiveness of LAIV co-administration with influenza antiviral medications has not been studied. However, because these antivirals reduce replication of influenza viruses, LAIV should not be administered until 48 hours after cessation of influenza antivirals, and influenza antiviral medications should not be administered for two weeks after receipt of LAIV.

LAIV must be stored in a refrigerator at 2°C to 8°C (35–46°F).

VACCINATION PROTOCOLS

Vaccination efficacy depends primarily on the age and the immune system of the recipient, whether the viruses in the vaccine match the viruses in circulation, and the outcome being measured. Individuals with moderate-to-severe febrile illness should not be vaccinated until their symptoms abate. However, minor illnesses with or without fever do not contraindicate use of influenza vaccine, particularly among children with mild upper-respiratory tract infection or allergic rhinitis.

Vaccine effectiveness is lower among previously unvaccinated children under 9 years of age if they have received only one dose of vaccine, compared with children who have received two doses. All children aged 6 months up to 9 years who have never been vaccinated with either LAIV or TIV should receive two doses of vaccine. Children in this age range who receive TIV should have a booster dose of TIV administered at least 1 month after the initial dose and before the onset of influenza season, if possible.

LAIV is to be used only as a nasal spray and should not be administered by the intramuscular, intradermal, or intravenous route. LAIV is supplied in a pre-filled single-use sprayer containing 0.5 mL of vaccine. Approximately 0.25 mL (half of the sprayer contents) is sprayed into the first nostril with the recipient in upright position. An attached dose-divider clip is removed from the sprayer to administer the second half of the dose into the other nostril. Even if the vaccine recipient sneezes after administration, the dose should not be repeated.

LAIV should be administered annually according to the following schedule:

• Children aged 2 up to 9 years previously unvaccinated at any time with either LAIV or TIV should receive two doses of LAIV separated by 6 to 10 weeks; if possible, the second dose of vaccine should be administered before the onset of influenza season.
• Children aged 2 up to 9 years previously vaccinated with either LAIV or TIV should receive one dose of LAIV. They do not require a second dose.
• Individuals aged 9 to 49 years should receive one dose of LAIV.

During periods when inactivated vaccine is in short supply, use of LAIV is encouraged when feasible for those eligible (including healthcare workers) in hopes of increasing availability of TIV for individuals in high-risk groups. Possible advantages of LAIV include its potential to induce a broad mucosal and systemic immune response, its ease of administration, and the general preference of nasal spray over injection.

Vaccine shortages do occur. When they do, the following populations have highest priority:

• All children 6 to 23 months
• Healthy children aged 24 to 59 months and their household contacts and out-of-home caregivers
• Adults 65 years and older
• Individuals 2 to 64 years with underlying chronic medical conditions
• All women who will be pregnant during the influenza season
• Residents of nursing homes and long-term care facilities
• Children ages 6 months to 18 years on chronic aspirin therapy
• Healthcare workers involved in direct client care
• Out-of-home caregivers and household contacts of children of ages under 6 months

The ACIP emphasizes that influenza vaccine should continue to be offered throughout the influenza season even after influenza has been documented in a community.

Contraindications for Influenza Vaccine

Individuals in the following groups should not receive influenza vaccine before talking with their doctor:

• Those with a severe allergy (ie, anaphylactic allergic reaction) to hens' eggs
• People who had onset of Guillain-Barré syndrome during the 6 weeks after receiving influenza vaccine

USING ANTIVIRAL AGENTS FOR INFLUENZA

Antiviral drugs for influenza are an adjunct to influenza vaccine for controlling and preventing influenza. These agents are not a substitute for vaccination. Although there is ongoing research on influenza on molecular virology, including studies by the Influenza Genome Sequencing Project, at present, only two classes of anti-viral drugs are available in the United States: neuraminidase inhibitors and M2 inhibitors (adamantine derivatives).

Neuraminidase Inhibitors

Neuraminidase inhibitors are antiviral drugs such as oseltamivir (Tamiflu) and zanamivir (Relenza). These drugs are designed to halt the spread of the virus in the body. They are effective against both influenza A and B and have been found to reduce symptoms and complications. Because different strains of influenza viruses have differing degrees of resistance to these antivirals, they may not be effective in a future pandemic.

M2 Inhibitors

M2 inhibitors are antiviral drugs such as amantadine and rimantadine. They are designed to block a viral ion channel (M2 protein) and prevent the virus from infecting cells. These drugs are sometimes effective against influenza A if given early in the infection but are not effective against influenza B. During the 2005–2006 influenza season, the CDC recommended against using M2 inhibitors.

INFECTION CONTROL MEASURES

The flu spreads in droplets from coughing and sneezing. It usually spreads from person to person, though occasionally people may become infected if they touch the mouth and nose after touching something with virus particles on it.

A combination of infection control strategies is recommended to decrease transmission of influenza in healthcare settings. These include influenza immunization for people at high risk for complications, immunization for healthcare workers, respiratory hygiene/cough etiquette, Standard Precautions and droplet precautions, and visitor and worker restrictions programs. Influenza clients should be given private rooms when possible and healthcare personnel should be encouraged to wear masks for close client contact (within 3 feet), and gowns and gloves if contact with respiratory secretions is likely.

The use of surgical or procedure masks by infectious clients may help contain their respiratory secretions and limit exposure to others. When a client is not wearing a mask (eg, in an isolation room), having healthcare personnel mask for close contact with the client may prevent nose and mouth contact with respiratory droplets. However, no studies have definitively shown that mask use by either infectious clients or healthcare personnel prevents influenza transmission.

In the United States, disposable surgical and procedure masks have been used widely in healthcare settings to prevent exposure to respiratory infections, but they have not been used commonly in community settings, such as schools or businesses, or at public gatherings.

CONCLUSION

Vaccination is the primary method for preventing influenza and its secondary complications. The introduction of live attenuated influenza vaccine (LAIV) administered intranasally is simplifying delivery of this crucial medication to a large segment of the population. Administration of antiviral medications, either for the early treatment of influenza infection or for prophylaxis, is a useful adjunct in the control of influenza.

Posted October 21, 2008

Expires October 1, 2009

Copyright © 2008 Wild Iris Medical Education. All rights reserved.

Accreditation   Home
Site Map   Contact   Privacy   Disclaimer

CriticalCareCEU.com is a division of Wild Iris Medical Education
© 2008 Wild Iris Medical Education, Inc.