#13,965
Normally by the end of March we are seeing the last gasp of the winter flu season, sometimes punctuated by a surge in late-season Influenza B cases. This year, however, is a departure from normal.
What began as a relatively mild, H1N1 flu season last fall has morphed into a more severe H3N2 season over the past 6 weeks, with a rapidly surging H3N2 3C.3a clade leading the charge (see graphic below).
We've been following this dramatic rise in 3C.3a for a couple of months, including in:
CDC FluView Week 11: Flu Season Continues Strong As H3N2 Continues To Climb
WHO Selects Fall H3N2 Flu Shot Component: Clade 3C.3a
CDC FLuView Week 8: Flu Remains Elevated - H3N2 Clade 3C.3a Continues Rise
WHO: (Partial) Recommended Composition Of 2019-2020 Northern Hemisphere Flu Vaccine
We'll get a new FluView report in a few hours, but yesterday afternoon the CDC released the following HAN (Health Alert Network) advisory, on late season H3N2, and advice to clinicians on the benefits of early treatment with antivirals.
Influenza Season Continues with an Increase in Influenza A(H3N2) Activity
Distributed via the CDC Health Alert Network
March 28, 2019 1415 ET (2:15 PM ET)
CDCHAN-00419
CDC reminds clinicians to have a high suspicion for influenza and recommends rapid antiviral treatment of high-risk patients with suspected influenza.
Summary
The Centers for Disease Control and Prevention (CDC) is issuing this health advisory to notify clinicians that influenza activity remains high in the United States, with an increasing proportion of activity due to influenza A(H3N2) viruses, continued circulation of influenza A(H1N1) viruses, and low levels of influenza B viruses. Influenza should be considered as a possible diagnosis for patients with respiratory illness while local influenza activity remains elevated. Because influenza A(H3N2) viruses may be associated with severe disease in older adults, this health advisory serves as a reminder that early empiric treatment with influenza antiviral medications is recommended for hospitalized and high-risk patients, especially those 65 years and older. Antiviral treatment should be started as soon as possible after illness onset and should not wait for laboratory confirmation.
Background
In the United States, influenza activity remains elevated and widespread, and the season is likely to last several more weeks (see CDC FluView report for details: https://www.cdc.gov/flu/weekly/index.htm). Earlier in the season, influenza A(H1N1) viruses were predominant in most of the country. Although A(H1N1) viruses continue to circulate and remain predominant for the season overall, during the three weeks ending March 16, influenza A(H3N2) viruses have been identified more frequently than A(H1N1) viruses in most of the country. In the past, A(H3N2) virus-predominant influenza seasons have been associated with more hospitalizations and deaths in people 65 years and older than A(H1N1) virus-predominant seasons. Influenza vaccine effectiveness is generally lower against influenza A(H3N2) viruses than against A(H1N1) or B viruses [1]. In addition, one genetic clade of A(H3N2) viruses, the 3C.3a clade, has recently become predominant among circulating A(H3N2) viruses and according to laboratory testing these viruses are antigenically distinct from the A(H3N2) virus included in this season’s vaccine.
CDC recommends antiviral medications for treatment of influenza, regardless of a patient’s influenza vaccination status. Antiviral treatment has been shown to have clinical and public health benefit in reducing illness and severe outcomes of influenza based on evidence from randomized controlled trials, meta-analyses of randomized controlled trials, and observational studies during past influenza seasons and during the 2009 H1N1 pandemic [2–9]. Influenza antiviral medications are most effective in treating influenza and reducing complications when treatment is started early (within 48 hours of illness onset). However, some studies suggest clinical benefit among hospitalized patients and young children with febrile illness even when treatment starts three to five days after illness onset [10–16].
Recommendations
All Hospitalized, Severely Ill, and High-Risk Patients with Suspected or Confirmed Influenza Should Be Treated with Antivirals
Antiviral treatment is recommended as early as possible for any patient with suspected or confirmed influenza who:1) Is hospitalized—treatment is recommended for all hospitalized patients;2) Has severe, complicated, or progressive illness—this may include outpatients with severe or prolonged progressive symptoms or patients who develop complications such as pneumonia but who are not hospitalized;3) Is at high risk for influenza complications but not hospitalized—this includes
Adults 65 years and older.
Antivirals in Non-High Risk Patients with Uncomplicated Influenza
- Children younger than two years. Although all children younger than five years are considered at higher risk for complications from influenza, the highest risk is for those younger than two years.
- People with chronic pulmonary (including asthma), cardiovascular (except hypertension alone), renal, hepatic, hematological (including sickle cell disease), and metabolic disorders (including diabetes mellitus).
- People with neurologic and neurodevelopment conditions (including disorders of the brain, spinal cord, peripheral nerve, and muscle such as cerebral palsy, epilepsy [seizure disorders], stroke, intellectual disability, moderate to severe developmental delay, muscular dystrophy, or spinal cord injury).
- People with immunosuppression, including that caused by medications or by HIV infection.
- Women who are pregnant or postpartum (within two weeks after delivery).
- People younger than 19 years who are receiving long-term aspirin therapy.
- American Indians and Alaska Natives.
- People with extreme obesity (i.e., body-mass index is equal to or greater than 40).
- Residents of nursing homes and other chronic-care facilities.
Antiviral treatment can benefit other individuals with influenza. While current guidance focuses on antiviral treatment of those with severe illness or at high risk of complications, antiviral treatment may be prescribed for any previously healthy (non-high risk) outpatient with suspected or confirmed influenza who presents within two days after illness onset. Clinical judgment—considering the patient’s disease severity and progression, age, likelihood of influenza, and time since onset of symptoms—is important when making antiviral treatment decisions for outpatients who are not at increased risk for influenza complications.(Continue . . . .)
