The Centers for Disease Control and Prevention (CDC), the American Academy of Family Physicians (AAFP), and several other health care professional organizations are urging physicians to resort earlier rather than later to administering uraminidase inhibitor antiviral medications when indicated for treatment and prevention of influenza as an adjunct to vaccination. The two prescription antiviral medications currently recommended for flu treatment or prevention are oseltamivir (Tamiflu) and zanamivir (Relenza), to be administered when influenza is suspected in patients belonging to categories at higher risk for complications as an adjunct to vaccination. These demographics include children younger than the age two and adult seniors aged 65 and older.
This extraordinary recommendation is being made in light of this year’s influenza vaccine being ill-matched with the predominant H3N2 flu strain so far in this year’s flu season, and believed to be providing considerably less than optimum prevention due to substantial antigenic and genetic drift among the dominant circulating H3N2 virus strain so far this winter.
A December 3, 2014, CDC Health Alert Network advisory reported that according to influenza viral characterization data collected and analyzed in the United States from Oct. 1 through Nov. 22, 48 percent of the H3N2 viruses observed were antigenically “like” this year’s H3N2 vaccine component, but fifty-two percent, were antigenically different, or had drifted, from the H3N2 vaccine virus. The CDC notes that in past seasons when influenza A (EG: H3N2) viruses have been dominant, higher overall and age-specific hospitalization rates and more mortality have been observed, especially among older people, very young children, and in persons with certain chronic medical conditions compared with seasons during which influenza A (H1N1) or influenza B viruses have predominated, and that In past seasons during which the predominant circulating influenza viruses have drifted, decreased vaccine effectiveness has been a consequence.
A Jan. 29 CDC “Dear Colleague” Antiviral Letter to Providers on Department of Health and Human Services Centers for Disease Control and Prevention letterhead asks for clinicians on the front lines to “think flu,” with a focus on reducing more severe flu outcomes like hospitalization and death, particularly among higher-risk group patients. The letter advises that influenza activity in the U.S. is running high overall and likely to continue for several weeks, with H3N2 viruses having been most common strain so far, and that there are typically more hospitalizations and deaths among children younger than two years and people 65 years and older during seasons when H3N2 viruses predominate. Consequently, they stress the importance of doing everything reasonably possible to protect people in these two age groups contracting this year’s flu.
“Evidence from past influenza seasons and the 2009 H1N1 pandemic has shown that treatment with neuraminidase inhibitors has clinical and public health benefit in reducing severe outcomes of influenza and, when indicated, should be initiated as soon as possible after illness onset,” the Dec. 3 advisory notes.
Notwithstanding this year’s vaccine’s evidently less-than-optimum effectiveness, estimated to be about 23 percent, and considerably less than that for some key demographics, the letter maintains that the first and most important step for flu prevention is getting a flu vaccine inoculation for persons older than six months. A one-in-four degree of protection is better than zero, and the vaccine still offers a higher degree of protection against contracting its three or four other target strains of influenza which may become more aggressive later in the season.
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However, in the context of widespread H3N2 circulation and reduced vaccine effectiveness, the letter emphasizes that “prompt antiviral treatment of severely ill and high risk patients becomes even more important as a second line of defense in reducing flu complications and death,” with antiviral treatment starting as soon as possible after illness onset, ideally, within 48 hours. Administration of oseltamivir or zanamivir is indicated for any patient with confirmed or suspected influenza who is hospitalized, has severe, complicated or progressive illness, or is at higher risk for influenza complications, and the CDC advisory emphasizes that starting antiviral treatment should not e delayed pending laboratory confirmation of influenza. Oseltamivir is approved to treat influenza in patients age two weeks and older and as a prophylactic agent against contracting influenza in patients age one year and older. Zanamivir is approved to treat flu in patients age seven years old and older, and as a flu preventative in patients aged five and older.
The letter also outlines several key points to for caregivers to consider about the importance of vaccination against and prompt treatment for flu, particularly in the high risk categories:
– Children younger than 2 years, and people 65 and older are at high risk for complications from the flu. These two age groups have the highest flu hospitalization rates.
– Antiviral drugs are an important second line of defense to treat flu illness, although not a satisfactory substitute for vaccination.
– Data indicate that flu antiviral drugs can reduce symptoms and prevent serious flu complications.
– For high risk patients, antiviral drugs can mean the difference between a milder illness and a hospital stay.
– Antiviral drugs are under-utilized. A recent study showed that only 19% of high risk outpatients who had the flu were treated with flu antiviral drugs.
– CDC recommends that all severely ill people and people who are at high risk of serious flu complications with suspected flu be treated with flu antiviral drugs as soon as possible (without confirmatory testing).
– Studies show that flu antiviral drugs work best for treatment when they are started within 2 days of getting sick. However, starting them later may still be helpful.
– Studies show that flu antiviral drugs work best for treatment when they are started within 2 days of getting sick. However, starting them later may still be helpful.
– There are three FDA-approved influenza antiviral drugs recommended by CDC this season. The brand names for these are Tamiflu (generic name oseltamivir), Relenza (generic name zanamivir), and Rapivab (generic name peramivir). Peramivir was approved in December 2014 and is given by IV.
Regarding supply of antiviral medications, the CDC says drug manufacturers have declared sufficient product stock on hand to meet projected high demand this 2014-2015 flu season, although noting that the agency and several influenza antiviral drug manufacturers are aware that there have been some spot shortages reported, specifically for Tamiflu (oseltamivir). They note that Tamiflu’s manufacturer Genentech is currently working with distributors and national retail pharmacy chains to supply consistent Tamiflu access, but advise patients to consider calling a pharmacy in advance to see if they have drug on their shelf before venturing out, noting that a pharmacy where the product is out of stock may still be able to identify another pharmacy in the area able to supply Tamiflu.
The CDC also says it will coordinate with commercial partners to facilitate the rapid resolution of large antiviral drug orders on order to assist long-term care facilities experiencing difficulty with antiviral drug access in institutional outbreak settings. Provisionally, the Division of Strategic National Stockpile (DSNS) has been available since January 12 from 7:00 a.m. to 7:00 p.m., EST Monday through Friday, to assist public health officials and health care institutions by coordinating with supply chain partners to rapidly redirect supply to identified locations with elevated need of these medicines, and the.CDC and FDA will continue working in concert with manufacturers to assess influenza antiviral drug supply.
Sources:
Centers for Disease Control and Prevention (CDC),
American Academy of Family Physicians (AAFP)