January 16, 2020 04:01 pm News Staff – On Jan. 10, the CDC issued a Health Alert Network advisory to notify physicians that seasonal influenza activity remains high in the United States, primarily due to heightened circulation of influenza B/Victoria viruses, but also to increasing circulation of influenza A(H1N1)pdm09 viruses. Circulating levels of influenza B/Yamagata and influenza A(H3N2) viruses remain low.
According to a Morbidity and Mortality Weekly Report Early Release published the same day that focused on how influenza B/Victoria viruses have affected children in Louisiana during the 2019-20 season, influenza B viruses have not predominated in the United States for nearly three decades.
Given the overall elevated influenza activity and the fact that both influenza A and B virus infections can cause severe disease and death, the CDC said its advisory aims to remind physicians that early treatment with antiviral medications can be critical to improving outcomes in patients with influenza, including children younger than age 2.
The agency also continues to recommend vaccinating all patients ages 6 months and older who haven't received the flu shot this season for as long as influenza viruses continue to circulate, which is expected to be several more weeks.
All hospitalized, severely ill and high-risk patients with suspected or confirmed influenza, regardless of their flu vaccine status, should be treated with antivirals as soon as possible after illness onset, the CDC advisory recommended.
Antiviral treatment may also be beneficial for previously healthy patients who present with suspected or confirmed influenza within two days after illness onset, the agency noted. Multiple randomized controlled clinical trials and meta-analyses of RCTs have demonstrated the efficacy of early treatment with neuraminidase inhibitors in reducing duration of fever and illness symptoms by about a day in otherwise healthy children and adults with uncomplicated influenza. Physicians' clinical judgment regarding patients' disease severity and progression, age, and other factors are key when making antiviral treatment decisions in these patients.
Four FDA-approved influenza antiviral medications are recommended for use in the United States during the 2019-20 influenza season.
They are the three neuraminidase inhibitors oseltamivir phosphate (an oral agent available as a generic or as Tamiflu), inhaled zanamivir (Relenza) and intravenous peramivir (Rapivab), as well as the newer oral medication baloxavir marboxil (Xofluza), which is active against both influenza A and B viruses but uses a different mechanism of action than the neuraminidase inhibitors.
The FDA approved baloxavir in October to treat acute uncomplicated influenza within two days of illness onset in patients 12 and older who are at high risk of developing influenza-related complications. Baloxavir was superior to placebo and had similar overall efficacy to oseltamivir in time to alleviation of symptoms in these patients, but no data are available for its use to treat influenza in pregnant women, immunocompromised people, those with severe disease or hospitalized patients.
The CDC provides dosing and detailed treatment considerations through its Influenza Antiviral Medications: Summary for Clinicians webpage.
According to the Jan. 10 MMWR, the CDC's November field investigation to characterize early influenza B virus-associated illnesses throughout Louisiana specifically sought to identify the influenza B virus subclades responsible for the outbreak.
The team performed a medical chart abstraction for 198 patients (173 outpatients and 25 hospitalized patients), median age 6 years, with laboratory-confirmed influenza B virus infection whose respiratory specimens were submitted to the Louisiana Public Health Laboratory between May 24 and Nov. 21, 2019. Most patient records originated from a single large pediatric care facility in New Orleans; the rest were from other sites scattered throughout the state.
Of 83 influenza B viruses sequenced from the 198 patient specimens, 81 (98%) belonged to the influenza B/Victoria V1A.3 subclade, which began circulating in the United States during the latter half of the 2018-19 influenza season.
It's important to note that none of the 198 patients had received the 2019-20 seasonal influenza vaccine, which the CDC said was at least in part due to flu activity beginning early, before influenza vaccine campaigns traditionally start. In fact, health care visits for influenza-like illness began to tick up in mid-August, with illness onset among the 198 patients occurring between May 24 and Oct. 29.
The MMWR concluded by reminding clinicians of the availability of resources such as HealthMap Vaccine Finder and Medfinder that can assist patients in identifying places to get age-appropriate influenza vaccines or fill prescriptions for influenza antivirals.
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