CDC: National ILI incidence drops slightly in fifth week of season

ATLANTA  — Has the 2016-2017 influenza season already peaked?



A little more five weeks into the season, and the Centers for Disease Control and Prevention on Friday reported the national weighted average of patient visits for influenza-like illness for the week ended Jan. 7 dropped slightly from 3.3% to 3.2%. For the last 15 seasons, the average duration of a flu season has been 13 weeks, the CDC reported.



In some seasons, flu incidence drops slightly one week before picking up in the next. Last year, the season peaked at about the 3.5% mark. The year before, ILI incidenced peaked at almost 6%.



The national baseline for ILI activity is 2.2%.



Currently, influenza activity is widespread across both coasts of the United States. According to CDC, New York City, Puerto Rio and eight states (Arizona, Georgia, Missouri, New Jersey, New York, Oklahoma, Oregon and South Carolina) experienced high ILI activity. Six states (Alabama, California, Louisiana, Nevada, Pennsylvania and Virginia) experienced moderate ILI activity.  



The most frequently identified influenza virus type reported by public health laboratories during the week ending January 7 was influenza A viruses, with influenza A (H3) viruses predominating.



The four components of this year's quadrivalent influenza vaccines appear to match up with the dominant strains. All 37 influenza A (H1N1)pdm09 viruses were similar to the influenza A (H1N1) component of the 2016-2017 Northern Hemisphere vaccine. And 95% of influenza A (H3N2) viruses that were antigenically characterized is comparable to the influenza A (H3N2) component of the 2016-2017 Northern Hemisphere vaccine.



Similarly, 90.3% B/Victoria-lineage viruses were antigenically characterized as B/Brisbane/60/2008-like, which is included as an influenza B component of the 2016-2017 Northern Hemisphere trivalent and quadrivalent influenza vaccines. And all 28 of the B/Yamagata-lineage viruses were antigenically characterized as B/Phuket/3073/2013-like, which is included as an influenza B component of the 2016-2017 Northern Hemisphere quadrivalent influenza vaccines.