The Pharmacist and Influenza

US Pharm. 2007;1:24-31.

Influenza is a major public health menace, infecting 5% to 20% of American residents per year and causing about 200,000 hospitalizations and 36,000 deaths each year in the United States.^1-4 Influenza and pneumonia are the sixth leading cause of U.S. deaths.⁵ In those 65 and older, it is the fifth most common cause of death.⁵ Thirty percent of nursing home residents who contract influenza will not survive.⁵ Some pharmacies have initiated vaccination programs to provide their patients with protection against the virus. It is therefore imperative that pharmacists be informed about the condition and its prevention and treatment.

Transmission of Influenza
The transmission of influenza is typical for respiratory diseases and is described in this month's patient leaflet. Once the virus enters the host, the host becomes infected after an incubation period of one to four days (mean time, two days).¹ The seeming inability of science to halt influenza outbreaks is partly because the infected host can produce contaminated droplets the day before onset of symptoms. This fact limits the usefulness of many public health measures (e.g., taking care when coughing and sneezing), as people who do not suspect they are infected carry on as usual, passing the illness to others. Adults continue to be infective for up to five days after onset of symptoms, but children can transmit the infection for 10 or more days.¹ People living in close contact with others are obviously at higher risk than those who are more isolated.⁵ Thus, transmission is facilitated among residents of dormitories, multiperson apartments, prisons, custodial care facilities, and nursing homes. Nursing home residents have a 60% risk of contracting influenza during an active epidemic.⁵

Manifestations of Influenza
Symptoms and signs begin suddenly. They are largely nonspecific, resembling other respiratory illnesses.^1,6 Manifestations are both respiratory and constitutional.^1,7 The respiratory manifestations include sore throat, nonproductive cough, and rhinitis, while fever, myalgia, headache, and malaise are among the constitutional manifestations. Children may also experience otitis media, diarrhea, nausea, and vomiting. In most patients, the symptoms remit after three to seven days. However, cough and malaise can persist for two weeks or more.

In patients with underlying medical conditions, such as pulmonary or cardiac disease, influenza may exacerbate the original condition, which increases the need to prevent influenza in these patients via vaccination. The condition can also lead to bacterial pneumonia or influenza viral pneumonia.

If young children with high-risk medical conditions contract influenza, their risk of morbidity is much higher. The hospitalization rate in children younger than 5 without high-risk conditions is 100 patients per 100,000. However, for children with high-risk conditions, rates are five times higher (500/100,000).¹

Vaccine Options
In the U.S., the two vaccines licensed for use against influenza are inactivated (TIV) and live and attenuated (LAIV).¹ The inactivated vaccine is given intramuscularly and is incapable of producing influenza manifestations. In contrast, LAIV is given intranasally and can produce mild manifestations. The inactivated vaccine is approved for healthy or unhealthy patients 6 months and older; LAIV is limited to healthy patients ages 5 to 49.

Benefits of Vaccine
Antibodies to influenza develop within two weeks postvaccination.³ The vaccine is 70% to 90% effective in healthy adults younger than 65.³ In other patients, vaccination is valuable in limiting the scope and severity of manifestations and in reducing the risk of adverse reactions. Vaccination is recommended for certain high-risk patients to prevent hospitalization and lower the risk of death. It also lowers the risk of respiratory illness and subsequent physician visits, which reduces absenteeism from work and school, lowering health care costs and increasing productivity.¹ In children, vaccination can lower the risk of otitis media, a possible result of influenza.¹

Who Should Receive the Vaccine?
In 2006, the CDC listed several groups who should obtain annual influenza vaccinations. One large group is patients at high risk for complications from influenza and who may experience more severe disease, such as children ages 6 to 59 months, women who will be pregnant during the influenza season, or those 50 or older.^1,3 Any patient with a chronic medical condition (e.g., pulmonary or cardiovascular problems such as asthma but excluding hypertension) is also at high risk. Patients should be vaccinated if they required regular medical appointments or hospitalizations during the previous year due to chronic medical diseases (e.g., diabetes mellitus), renal dysfunction, hemoglobinopa­thies, or immunodeficiency from any cause. Patients with conditions prone to compromise respiratory function or that increase the risk for aspiration (e.g., cognitive dysfunction, spinal cord injury, seizure disorders, other neuromuscular disorders) should be vaccinated. Other high-risk patients are children and adolescents ages 6 months to 18 years who are receiving long-term aspirin therapy and would have a risk of Reye's syndrome if they contact influenza.

Vaccinations are also recommended for anyone living with or caring for high-risk patients, such as household contacts or health care workers. For the latter group, annual vaccination helps prevent transmission to members of the high-risk groups.⁸ However, a recent study published as a part of the well-respected Cochrane Collaboration explored the quality of evidence to prove whether vaccinating health care workers affected the incidence of influenza, influenza-like illnesses, and their complications in elderly residents of long-term care facilities.⁹ The authors were not able to locate credible evidence that vaccinating healthy medical employees younger than 60 who care for the elderly reduced influenza complications in the el­der­ly patients. Despite this finding, the recommendation for vaccination of health care workers will likely remain a core part of the CDC guidelines.

When children between ages 6 months and 9 years are to be vaccinated for the first time, it is important to give two doses of influenza vaccine, separated by at least one month, to ensure full protection.¹⁰

Reactions and Contraindications to Vaccine
With TIV, pharmacists can tell patients that they may experience soreness, erythema, or inflammation at the injection site, as it occurs in 10% to 64% of vaccinees.^1,4 The duration is usually less than 48 hours postvaccination. Body aches, low-grade fever, and malaise may occur. LAIV may cause rhinorrhea, headache, fever, vomiting, or myalgia in children, and rhinorrhea, headache, sore throat, and cough in adults.⁴

TIV should be avoided in patients younger than 6 months and in those with anaphylactic sensitivity to eggs or other components of the vaccine.¹ LAIV should not be given to those younger than 5 or those 50 and older, pregnant women, those with a history of hypersensitivity (including anaphylaxis) to components of LAIV or to eggs, those with a history of Guillain-Barré syndrome, or children or adolescents receiving aspirin or other salicylates. It should also not be given to those with asthma, reactive airways disease, or other chronic cardiovascular or pulmonary disorders, as well as in those with underlying medical conditions such as diabetes, renal dysfunction, hemoglobinopathies, known or suspected immunodeficiency diseases or those receiving immunosuppressive therapies.

Vaccine is contraindicated for children younger than six months old, but they may be protected by a strategy known as "cocooning."³ Using this technique, all persons who come into contact with the baby should be vaccinated, including day care workers, babysitters, and all other close contacts. This approach creates a safe cocoon or zone of protection around the child.¹⁰

Breast-feeding is not a contraindication to the influenza vaccination, and TIV is safe for breast-feeding mothers and their infants. However, the safety of LAIV in breast-feeding is unknown, because it might be excreted in breast milk and because the mother might shed the live vaccine virus to a nursing child.¹

The Need for Annual Vaccination
Consumers may ask the pharmacist why experts recommend yearly influenza vaccination. Influenza vaccination is considered protective only for one season.¹¹ The virus mutates each year through a method known as "antigenic drift." This creates several dilemmas. People may suffer from many episodes of influenza during their lifetime, as there is usually little to no immunity from a previous bout. Furthermore, new vaccines are created each year using projections of which virus strains will be most active for that year. While the vaccines used in 2006/2007 may provide protection for this season, their efficacy for the 2007/2008 season cannot be ensured. Finally, a patient's immunity lessens each year following vaccination, irrespective of the prevalent circulating viral strain, making yearly "boosters" a medical necessity.

Antiviral Medications
The FDA has approved several antivirals for influenza,¹² including the M2 ion channel inhibi­ tors, such as amantadine (Symmetrel) and rimantadine (Flumadine), which have both been used in prophylaxis and treatment of influenza A. Neuraminidase inhibitors oseltamivir (Tamiflu) and zanamivir (Relenza) are approved for both prophylaxis and treatment of influenza A and B. However, for the 2005/2006 season, the CDC advised against the use of M2 antivirals because of resistance.¹³ Regarding the 2006/2007 season, the CDC states that "a high proportion of currently circulating influenza A viruses in the United States have developed resistance to amantadine and riman­tadine."¹⁴

References

1. CDC. Prevention and control of influenza. Available at: www.cdc.gov/mmwr/preview/mmwrhtml/rr5510a1.htm. Accessed November 30, 2006.

2. Davis MM, Taubert K, Benin AL, et al. Influenza vaccination as secondary prevention for cardiovascular disease: a science advisory from the American Heart Association/American College of Cardiology. J Am Coll Cardiol. 2006;48:1498-1502.

3. Bren L. Influenza: vaccination still the best protection. U.S. Food and Drug Administration. Available at: www.fda.gov/fdac/features/2006/506_influenza.html. Accessed November 30, 2006.

4. CDC. Key facts about influenza (flu) vaccine. Available at: www.cdc.gov/flu/protect/keyfacts.htm. Accessed November 30, 2006.

5. Zimmerman RK. Recent changes in influenza epidemiology and vaccination recommendations. J Fam Pract. 2005;54(Suppl):S1-S8.

6. Call SA, Vollenweider MA, Hornung CA, et al. Does this patient have influenza? JAMA. 2005;293:987-997.

7. CDC. Questions and answers: the disease. Available at: www.cdc.gov/flu/about/qa/disease.htm. Accessed November 30, 2006.

8. Thomas RE, Jefferson TO, Demicheli V, et al. Influenza vaccination for health-care workers who work with elderly people in institutions: a systematic review. Lancet Infect Dis. 2006;6:273-279.

9. Thomas RE, Jefferson T, Demicheli V, et al. Influenza vaccination for healthcare workers who work with the elderly. Cochrane Database Syst Rev. 2006;3:CD005187.

10. Bren L. Getting ready for another flu season. Food and Drug Administration. Available at: www.fda.gov/fdac/features/2006/406_flu.html. Accessed November 30, 2006.

11. CDC. Questions and answers: flu vaccine. Available at: www.cdc.gov/flu/about/qa/fluvaccine.htm. Accessed November 30, 2006.

12. CDC. Influenza symptoms, protection, and what to do if you get sick. Available at: www.cdc.gov/flu/symptoms.htm. Accessed November 30, 2006.

13. CDC. CDC health alert. Available at: www.cdc.gov/flu/han011406.htm. Accessed November 30, 2006.

14. CDC. Antiviral drugs and influenza. Available at: www.cdc.gov/flu/protect/antiviral. Accessed November 30, 2006.

15. Luke CJ, Subbarao K. Vaccines for pandemic influenza. Emerg Infect Dis. 2006;12:66-72.

16. Lee VJ, Fernandez GG, Chen MI, et al. Influenza and the pandemic threat. Singapore Med J. 2006;47:463-470.

17. van der Wouden JC, Bueving HJ, Poole P. Preventing influenza: an overview of systematic reviews. Respir Med. 2005;99:1341-1349.

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