The CDC recently noted a significant increase in influenza activity over the past several weeks in the United States.
In a health advisory, the agency reminded clinicians that influenza should be high on their list of possible diagnoses for ill patients. They advised that all hospitalized patients and any high-risk patients — such as those aged younger than 2 years or older than 65 years — with suspected or confirmed influenza should be treated as soon as possible with antiviral medications.
“While antiviral drugs work best when treatment is started within 2 days of illness onset, clinical benefit has been observed even when treatment is initiated later,” the agency said.
Most of the country has reported widespread influenza activity by now. In its most recent update, the CDC reported that activity is high in 21 states, including much of the Midwest and South.
Influenza A(H3N2), which is known to evade the seasonal vaccine, remains the most prevalent strain in the U.S. this season. According to the CDC, 8.1% of the 261,076 specimens tested in clinical laboratories as of Dec. 23 were positive for influenza, including 81.5% that tested positive for influenza A. Among influenza A viruses that were subtyped by public health laboratories, 90.2% were H3N2 viruses.
Experts have expressed concern about surveillance data from Australia that showed the H3N2 component in the Southern Hemisphere’s influenza vaccine — the same one used in the Northern Hemisphere — was only 10% effective. But a CDC official previously told Infectious Disease News that the agency believes recent data from the U.S. are a better barometer of how the vaccine will perform in the states. The same H3N2 component used in last year’s vaccine was 32% effective against the strain — only slightly lower than the overall vaccine effectiveness of 39%.
In virus samples collected this season, the CDC has not recorded any drug resistance to the three neuraminidase inhibitor antivirals approved by the FDA. The antivirals include oseltamivir, commonly known as Tamiflu (Roche), which was approved as a generic last year, Relenza (zanamivir, GlaxoSmithKline) and Rapivab (peramivir, BioCryst). – by Gerard Gallagher
CDC. Seasonal influenza A(H3N2) activity and antiviral treatment of patients with influenza. https://emergency.cdc.gov/han/han00409.asp. Accessed December 29, 2017.