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Swine Flu Update 2014

Hayley Gray, PharmD Intern, Andrew J. Burris, PharmD, and Jennifer K. Seltzer, PharmD

January 23rd, 2014

In 2009, the nation was struck with a particularly unpredictable flu season due to the emergence of the "swine flu" or "novel H1N1." Responsible for more than 2,100 deaths in the United States, the virus caused global outbreak and was classified a pandemic by the World Health Organization.1 With this year's flu season peak reaching maximum intensity over the next several weeks, H1N1 has already claimed six pediatric lives in Texas. Since October 2013, 3,700 laboratory-confirmed influenza hospitalizations have been reported and that number is expected to rise.2To date, influenza A (H1N1) viruses have predominated, accounting for 97% of positive flu test results.2 Pharmacists serving on the front line of prevention should remain diligent in educating patients on the importance of vaccination.

The influenza virus consists of eight different segments of RNA.3It is these many different genes that allow the virus to alter its structure and on occasion, even mutate. Influenza is further subdivided into three virus types: A, B, and C. Influenza A is also named by the glycoproteins (hemagglutinin (H) and neuraminidase (N)) located on its cell surface.3 When two viruses infect the same host, they are able to communicate with one other and exchange genes during replication.3 The worst culmination of this occurred, in 2009, when two separate swine-origin viruses gave birth to what is today known as H1N1.

Swine influenza virus or "swine flu" causes respiratory infection in pigs. Similar to human influenza virus, there are multiple types and strains. The predominant strain that causes many outbreaks among swine is influenza type A. The major strains circulating in most recent years are:

While swine influenza virus does not commonly infect human hosts, when this does occur, the virus is known as a "variant" and is identified by adding the letter "v" to the end of the virus subtype. Several variant viruses (H1N1v and H3N2v) have been detected in the United States.4        

Everyone 6 months and older should receive an annual influenza vaccination as recommended by the Centers for Disease Control and Prevention (CDC), unless the patient has a history of a severe allergic reaction to any of the influenza vaccine components. Individuals who have not yet been vaccinated this season should still get an influenza vaccine as soon as possible. There are several flu vaccination options for the 2013-2014 flu season, all of which contain the 2009 H1N1 strain (see Table 1).5

 

 

 

Table 1. Influenza Vaccines—United States, 2013-2014 influenza season5,6

Vaccine

Trade name(s)

Protects against two influenza A viruses and one influenza B virus

  • An A/California/7/2009(H1N1) pdm09-like virus
  • An A(H3N2) virus antigenically like the cell-propagated prototype virus A/Victoria/361/2011
  • A B/Massachusetts/2/2012-like virus

Inactivated Influenza Vaccine,Trivalent (IIV3)
Standard Dose

Afluria®, Fluarix®, Flucelvax®, FluLaval®, Fluvirin®, Fluzone®, Fluzone®(Intradermal)

Inactivated Influenza Vaccine,Trivalent (IIV3)
High Dose

Fluzone® High-dose

Recombinant Influenza Vaccine,Trivalent (RIV3)

FluBlok®

Protects against two influenza A viruses (H1N1, H3N2) and two influenza B viruses

  • Addition of a B/Brisbane/60/2008-like virus

Inactivated Influenza Vaccine,Quadrivalent (IIV4)

Fluarix® Quadrivalent, FluLaval® Quadrivalent, Fluzone® Quadrivalent 

Live-attenuated Influenza Vaccine,Quadraivalent(LAIV4)

Flumist®

Other flu preventative measures include frequent hand-washing with warm water and soap after touching common surfaces, avoiding close contact with people feeling ill, covering the nose and mouth with a tissue when coughing or sneezing, and staying home when experiencing flu-like symptoms. While vaccination is the best form of prevention, treatment with antiviral medications is an important second line of defense for those who become ill.3

Antiviral treatment is recommended for patients with confirmed or suspected influenza who are either hospitalized, have severe progressive illness, or are at higher risk for influenza-associated complications (e.g., children younger than 2 years, adults 65 years and older, patients with comorbidities, immunosuppressed patients, pregnant women, American Indians/Alaska Natives, morbidly-obese patients, residents of nursing homes and long- term care facilities).5,7 Antiviral treatment should be started ideally within 48 hours of symptom onset, as clinical benefit is greatest when administered early. When administered early, antiviral treatment may shorten the duration of symptoms, reduce the risk of influenza-associated complications, as well as shorten the duration of hospitalization. The two antiviral medications recommended are oseltamivir (Tamiflu®) and zanamivir (Relenza®).  These neuraminidase inhibitors have activity against both influenza A and B viruses.  When there is clinical suspicion, treatment should not be withheld while waiting for laboratory confirmation of influenza. Clinicians should consider antiviral treatment even when the rapid influenza diagnostic test is negative, because false negative results are common during influenza season.8

Since October 1 2013, 1,553 influenza A (2009 H1N1), 85 influenza A (H3N2), and 20 influenza B virus samples nationally have been tested for resistance to oseltamivir. So far this season, 13 out of 1,553 2009 H1N1 viruses have shown resistance to oseltamivir. Of tested samples, none were resistant to zanamivir (see Table 2).7 Texas is one of the states in which oseltamivir-resistant 2009 H1N1 virus has been detected.9

 

Table 2.  Neuraminidase inhibitor resistance testing results on samples collected (since 10/1/2013)7

 

Oseltamivir

Zanamivir

 

Virus samples tested (n)

Resistant viruses, number (%)

Virus samples tested (n)

Resistant viruses, number (%)

Influenza A (H3N2)

85

0 (0.0)

85

0 (0.0)

Influenza B

20

0 (0.0)

20

0(0.0)

2009 H1N1

1553*

13 (0.8)

709

0 (0.0)

*Includes specimens tested in national surveillance as well as public health laboratories in 16 states (AZ, CO, DE, FL, GA, HI, MA, ME, MD, MI, NY, PA, TX, UT, WA, WI) who share testing results with CDC

Intravenous zanamivir is the recommended antiviral treatment for severely ill patients with highly suspected or confirmed oseltamivir-resistant 2009 H1N1 virus infection.9 Intravenous peramivir, an investigational neuraminidase inhibitor in Phase 3 clinical trials, is another option for hospitalized patients with severe H1N1 infection. It has been used successfully in both adults and children under an emergency investigational drug program in the United States, and is associated with recovery in the majority of patients.10

While it is not possible to determine which influenza virus will dominate for the rest of the 2013-2014 influenza season, the influenza A (H1N1) pdm09 (pH1N1) virus appears to be the most common circulating virus to date. Healthcare personnel are at an increased risk of occupational exposure, and should be encouraged to follow necessary precautionary measures. For more information about swine flu, visit the CDC 2009 H1N1 flu website at www.cdc.gov/h1n1flu/ .

 

References:

  1. Centers for Disease Control and Prevention. 2009-2010 Influenza (flu) season questions & answers. Available at: http://www.cdc.gov/flu/pastseasons/0910season.htm .   Accessed January 7, 2014.
  2. Centers for Disease Control and Prevention. Situation update: summary of weekly fluview. Available at: http://www.cdc.gov/flu/weekly/summary.htm .  Accessed January 7, 2014.
  3. Labella AM, Merel SE. Influenza. Med Clin N Am. 2013;97:621-645.
  4. Centers for Disease Control and Prevention. Information on swine influenza/variant influenza viruses. Available at: http://www.cdc.gov/flu/swineflu/index.htm.  Accessed January 21, 2014.
  5. Centers for Disease Control and Prevention. Notice to clinicians: early reports of pH1N1-associated illnesses for the 2013-2014 influenza season. Available at: http://emergency.cdc.gov/HAN/han00359.asp.  Accessed January 7, 2014.
  6. Centers for Disease Control and Prevention. Summary recommendations: prevention and control of influenza with vaccines: recommendations of the advisory committee on immunization practices (ACIP) United States, 2013-2014. Available at: http://www.cdc.gov/flu/professionals/acip/2013-summary-recommendations.htm#primary-changes.  Accessed January 7, 2014.
  7. Centers for Disease Control and Prevention.  Seasonal influenza (flu).  Available at:  www.cdc.gov/flu/weekly/.  Accessed January 23rd, 2014.
  8. Texas Department of State Health Services. Influenza Health Alert (December 20, 2013). Available at: http://www.recombinomics.com/News/12211303/H1N1_Texas_Alert.html. Accessed January 21, 2014.
  9. Centers for Disease Control and Prevention. Situation update: summary of weekly FluView. Available at: http://www.cdc.gov/flu/weekly/summary.htm.  Accessed January 7, 2014.
  10. Hernandez JE, Adiga R, Armstrong R, et al. Clinical experience in adults and children treated with intravenous peramivir for 2009 influenza A (H1N1) under an emergency IND program in the United States. Clin Infect Dis. 2011;52(6):695-706.

  

 

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Last Reviewed: February 10, 2014
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