Prevention and Treatment of Influenza

Ms. Terrie is a clinical pharmacy writer based in Haymarket, Virginia.

In the United States, annual epidemics of influenza usually occur during the fall or winter months, but the peak of influenza activity can occur as late as April or May.¹ According to statistics from the Centers for Disease Control and Prevention (CDC), each year in the United States an estimated 5% to 20% of the population gets influenza and more than 200,000 people are hospitalized from flu complications.^1-3 Furthermore, an estimated 36,000 people die annually from complications of influenza, and approximately 90% of those deaths affect individuals 65 years and older.^1,3,4

On July 17, 2008, the CDC released Prevention and Control of Influenza Recommendations from the Advisory Committee on Immunization Practices (ACIP) regarding the use of influenza vaccine and antiviral agents. The 2008 recommendations included the 5 following principal updates or changes¹:

1. Annual vaccination should be completed for all children aged 5 to 18 years.
2. Annual vaccination of all children aged 6 months to 4 years (up to 59 months old) should continue to be a primary focus of vaccination efforts, because these children are at higher risk for developing complications from influenza. In addition, children aged 6 months to 8 years who have not been vaccinated previously at any time with at least 1 dose of either live, attenuated influenza vaccine (LAIV) or trivalent inactivated influenza vaccine (TIV) should receive 2 doses of ageappropriate vaccine in the same season, with a single dose during subsequent seasons.¹
3. Either TIV or LAIV can be used when vaccinating healthy individuals between the ages of 2 and 49 years of age. The LAIV should not be administered to children aged younger than 5 years with possible reactive airway disease. It is recommended that these children, as well as individuals at higher risk for influenza complications because of underlying medical conditions, children aged 6 to 23 months, and persons older than 49 years, should receive TIV.¹
4. The 2008-2009 trivalent vaccine virus strains are A/Brisbane/59/ 2007 (H1N1)-like, A/Brisbane/10/ 2007 (H3N2)-like, and B/Florida/4/ 2006-like antigens.¹
5. Although oseltamivir-resistant influenza A (H1N1) strains have been identified in the United States and some other countries, oseltamivir or zanamivir will continue to be the recommended antiviral medications for treatment of influenza, because other influenza virus strains remain sensitive to oseltamivir, and resistance levels to other antiviral medications remain high.¹

Certain patient populations, such as the elderly, pediatric patients, pregnant women, and individuals with certain medical conditions (eg, asthma, diabetes, or cardiovascular disease), are more susceptible to developing complications.^3,5 Complications of the flu can include bacterial infections, such as pneumonia, otitis media, sinus infections, and dehydration, and can exacerbate certain medical conditions (eg, congestive heart failure, asthma, and diabetes).^3,5

Signs, Symptoms, and Transmission of the Virus

The incubation period of the flu can range from 1 to 4 days. The onset of flu symptoms can be mild or severe. The typical influenza symptoms in adults may include abrupt onset of chills, headache, high fever, fatigue, dry cough, sore throat, rhinorrhea, and generalized aches and pains, especially in the back and legs.^5-7 Gastrointestinal symptoms, such as nausea, vomiting, and diarrhea also may occur.^5-7

The influenza virus can be transmitted via airborne transmission of respiratory droplets, direct contact with an infected person, or through contact with contaminated objects.^5,6 Many healthy individuals can transmit the flu to other individuals beginning on the first day prior to the development of symptoms and up to 5 days after becoming sick.^5-7

Prevention, Control, and Treatment of Influenza

For individuals who wish to decrease their risk of getting influenza, the single best method for preventing influenza is through yearly vaccination, as is recommended by the ACIP and the CDC. Moreover, the ACIP recommends that certain patient populations receive the flu vaccination each year, including individuals at high risk for developing complications from the flu, like children aged 6 months to 18 years; pregnant women; people aged 50 years and older, or those of any age with certain chronic medical conditions; individuals with sickle cell anemia and other hemoglobinopathies; people who have a weakened immune system; and people who receive longterm treatment with steroids for any condition; as well as people who live with or care for those at high risk for developing complications from the flu.^1,6,8-11

Certain patient populations should not be vaccinated until they have consulted with their primary health care provider, including individuals with severe allergy to chicken eggs; those who have had a severe reaction to an influenza vaccination in the past; individuals who developed Guillain-Barr? syndrome within 6 weeks of getting a previous influenza vaccine; and individuals who have a moderate or severe illness with a fever. In addition, influenza vaccine is not approved for use in children younger than 6 months of age.^1,6,8,10

Vaccinations

According to the CDC, each year the seasonal influenza vaccine contains 3 influenza virus strains—one influenza A (H3N2) virus, one influenza A (H1N1) virus, and one influenza B virus. The viruses used in creating flu vaccine are selected each year based on information gathered over the previous year about the strains of flu viruses that are infecting humans and how they are changing.^8,9 For the recommended vaccine for the 2008-2009 flu season, all 3 vaccine virus strains were changed from the 2007-2008 season.¹¹ Both TIV and LAIV prepared for the 2008-2009 flu season include A/Brisbane/59/2007 (H1N1)-like, A/Brisbane/10/2007 (H3N2)-like, and B/Florida/4/2006-like antigens.^1,12 Approximately 2 weeks after an individual is vaccinated, antibodies develop that protect against the virus.^7,8

As noted previously, 2 types of influenza vaccine are available. The TIV is administered via intramuscular injection and is also commonly known as the flu shot. The flu shot is approved for use in individuals older than 6 months, including healthy people and those with chronic medical conditions. Adults and older children should be vaccinated in the deltoid muscle; whereas infants and young children should be vaccinated in the anterolateral aspect of the thigh.^1,13

The second type of vaccine is the LAIV. LAIV is approved for use in healthy, nonpregnant individuals, aged 2 to 49 years.^12,14,15 The LAIV may be administered in individuals with minor illness. If nasal congestion is present, the delivery of the vaccine to the nasal lining may be limited; therefore it is suggested that vaccination should be delayed until nasal congestion is reduced.^13,14 Common adverse effects in children and adolescents include nasal congestion, fever, and headaches. Common adverse effects in adults include sore throat, fatigue, fever, and chills.^12,13,15

Recommended Antiviral Drugs for the 2008-2009 Season

Although yearly vaccination with the flu vaccine is the primary strategy for preventing the influenza virus, antiviral medications with activity against influenza viruses can be effective for the prevention and treatment of influenza (Table^14-20).

The 2 FDA-approved antiviral influenza medications available for use in the United States for the 2008-2009 season are oseltamivir (Tamiflu; Roche) and zanamivir (Relenza; GlaxoSmithKline).¹⁸ These agents are classified as neuraminidase inhibitors that have activity against both the A and B viruses.¹⁸

In addition, the CDC recommends against the use of the adamantanes for the treatment or prevention of influenza in the United States during the 2008-2009 influenza season, due to an increase in drug resistance.¹ For information on this issue, please visit the CDC's Web site at www.cdc.gov/flu/professionals/antivirals/agents.htm.

Conclusion

Each year, before flu season begins, pharmacists can assist their patients by reminding them to get their flu vaccinations, especially those patients in high-risk groups. Patients also should be reminded about practicing good infection control procedures, such as routine hand washing. In general, the majority of individuals who get the flu will typically recover fully within 1 to 2 weeks without complications.

In an effort to stress the importance of getting vaccinated, the CDC has announced that December 8-14, 2008, is National Influenza Vaccination Week. For more information on the influenza virus and the 2008-2009 influenza season, please visit the CDC Web site at www.cdc.gov/flu/

References

1. Prevention and Control of Influenza. Recommendations of the Advisory Committee on Immunization Practices (ACIP), 2008. MMWR Morb Mortal Wkly Rep. 2008;57(RR-7). Centers for Disease Control and Prevention Web site. www.cdc.gov/mmwr/pdf/rr/rr5707.pdf. Accessed October 5, 2008.
2. CDC promotes national influenza vaccination week to encourage flu vaccination throughout the influenza season. Centers for Disease Control and Prevention Web site. www.cdc.gov/media/pressrel/2007/r071123.htm. Accessed October 4, 2008.
3. Prevent the flu: get vaccinated. Centers for Disease Control and Prevention Web site. www.cdc.gov/Features/FluPrevention/. Accessed October 6, 2008.
4. Flu season summary (September 30, 2007-May 17, 2008). Centers for Disease Control and Prevention Web site. www.cdc.gov/flu/about/qa/season.htm. Accessed October 4, 2008.
5. Influenza Symptoms. Protection and What to Do If You Get Sick. Centers for Disease Control and Prevention Web site. www.cdc.gov/flu/pdf/symptoms.pdf. Accessed on October 4, 2008
6. Beers Mark et al. Infectious Diseases. The Merck Manual of Diagnosis and Therapy 18th Edition. Section 14, pp 1195-1198.
7. Flu Facts for Healthcare Professionals. FluFacts website. Available at. www.flufacts.com/hcp/default.aspx. Accessed on October 6, 2008
8. Key Facts About Seasonal Flu Vaccine. Centers for Disease Control website. Available at www.cdc.gov/flu/protect/keyfacts.htm.
9. Seasonal Influenza Vaccination Resources for Health Professionals. Persons for Whom Annual Vaccination is Recommended Centers for Disease Control website. Available at www.cdc.gov/flu/professionals/vaccination/index.htm#composition. Accessed on October 4, 2008
10. Influenza Vaccine. MedlinePlus website. Available at www.nlm.nih.gov/medlineplus/ency/article/002025.htm. Accessed on October 6,2008
11. Influenza Vaccine Composition & Major Differences. Centers for Disease Control website. Available at www.cdc.gov/flu/professionals/acip/composition0809.htm
12. Recommendations for Using TIV and LAIV During the 2008-09 Influenza Season. Centers for Disease Control website. Available at www.cdc.gov/flu/professionals/acip/recommendations.htm
13. Dosage, Administration and Storage. Centers for Disease Control website. Available at www.cdc.gov/flu/professionals/acip/dosage.htm. Accessed on October 6, 2008
14. The Nasal-Spray Flu Vaccine (LAIV). Centers for Disease Control website. Available at www.cdc.gov/flu/about/qa/nasalspray.htm.
15. FluMist Package Insert. Available at www.flumist.com.
16. Selecting the Viruses in the Influenza Vaccine. Centers for Disease Control website. Available at www.cdc.gov/flu/professionals/vaccination/virusqa.htm.
17. Seasonal Influenza Vaccine Supply for the U.S. 2008-2009 Influenza Season. Centers for Disease Control website. Available at www.cdc.gov/flu/about/qa/vaxsupply.htm#table. Accessed on October 4, 2008
18. Influenza Antiviral Medications: Summary for Clinicians. Centers for Disease Control website. Available at www.cdc.gov/flu/professionals/antivirals/summary-clinicians.htm. Accessed on October 6, 2008
19. Tamiflu package insert. Available at www.tamiflu.com/treat.aspx.
20. Relenza package insert. Available at us.gsk.com/products/assets/us_relenza_pil.pdf.