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Flu widespread in US; no antiviral resistance reported
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Influenza is widespread across virtually the entire continental United States this season, and H3N2 remains the dominant circulating strain, CDC officials said during a Grand Rounds presentation.
“This is something we don’t normally see, but the take-home message is that the flu is in a lot of places at the same time,” Daniel B. Jernigan, MD, MPH, director of the CDC’s Influenza Division, said during the live-streamed presentation.
H3N2 influenza is associated with higher numbers of cases, hospitalizations and deaths than other strains that are circulating.
Jernigan said that earlier this season, 339,598 clinical visits due to influenza-like illness were reported in the U.S. The H3N2 strain — against which vaccines have been significantly less effective — has been clearly dominant. Out of nearly 12,500 positive influenza tests reported this season, H3N2 accounted for 78% of cases. Of 10,874 positive tests for influenza A viruses, H3N2 accounted for 90% of cases, Jernigan said.
However, there has been no evidence of resistance to antivirals, he added.
Alicia M. Fry, MD, MPH, a team leader for the CDC’s Influenza Prevention and Control Team, highlighted the H3N2 strain’s penchant for eluding vaccines. Pooled vaccine effectiveness against the strain has been 33%, compared with 54% against influenza B viruses and 61% against A(H1N1)pdm09 viruses.
Nonetheless, vaccinations last season prevented many poor outcomes, Fry said. For example, they averted 5.3 million illnesses, 2.6 million outpatient visits and 84,600 hospitalizations in the 2016-2017 season.
She added that antivirals are what she called a “second line of defense” against influenza. CDC guidance on antiviral treatment is aimed at fighting or preventing severe illness. The agency recommends antiviral treatment as early as possible for any patient with suspected or confirmed influenza who is hospitalized; has severe, complicated or progressive illness; or is at high risk for influenza complications.
Antiviral treatment can be considered for any previously healthy, symptomatic outpatient who is not at high risk for complications and has confirmed or suspected influenza on the basis of clinical judgment. The patient should be treated within 48 hours of illness onset in those instances, the CDC advised.
The agency added that, although the U.S. should have enough antivirals for this season, some manufacturers have reported delays in filling orders. Additionally, there were antiviral shortages in some places with high levels of influenza activity.
Pharmacy staff may have to inquire with several manufacturers to obtain drugs. Patients may wish to call their pharmacies to ensure the drugs are available, the CDC said. – by Joe Green
Disclosures: Fry and Jernigan report no relevant financial disclosures.