CDC Flu Update: Activity Continues to be Low Across U.S.

According to this week’s FluView report from the Centers for Disease Control and Prevention (CDC), overall seasonal influenza activity is low across the United States. CDC recommends an annual flu vaccine for everyone 6 months of age and older. Getting vaccinated before flu activity begins is best.

For the week ending Oct. 31, 2015, the proportion of people seeing their health care provider for influenza-like illness (ILI) is 1.4% and remains below the national baseline (2.1%). All 10 U.S. regions reported ILI activity below region-specific baseline levels. Puerto Rico experienced low ILI activity. New York City and all 50 states experienced minimal ILI activity. The District of Columbia did not have sufficient data to calculate an activity level. ILI activity data indicate the amount of flu-like illness that is occurring in each state. Guam reported regional influenza activity. Two states (Georgia and Iowa) reported local influenza activity. Puerto Rico and 40 states reported sporadic influenza activity. The U.S. Virgin Islands, the District of Columbia, and 8 states reported no influenza activity. Geographic spread data show how many areas within a state or territory are seeing flu activity.

Influenza-associated hospitalization data from the Influenza Hospitalization Surveillance Network (FluSurv-NET) for the 2015-2016 influenza season will be updated weekly starting later this season.

The proportion of deaths attributed to pneumonia and influenza (P&I) based on the NCHS Mortality Surveillance System and the 122 Cities Mortality Reporting System is below their system-specific epidemic threshold. At this time, no influenza-associated pediatric deaths have been reported for the 2015-2016 flu season. Nationally, the percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories during the week ending October 31 was 1.3%. For the most recent three weeks, the regional percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories ranged from 0.3% to 2.6%. The most frequently identified influenza virus type reported by public health laboratories during the week ending October 31 was influenza A viruses, with influenza A (H3) viruses predominating. During the week ending October 31, 23 (79.3%) of the 29 influenza-positive tests reported to CDC by public health laboratories were influenza A viruses and 6 (20.7%) were influenza B viruses. Of the 20 influenza A viruses that were subtyped, 18 (78.3%) were H3 viruses and two (8.7%) were A (H1N1)pdm09 viruses.

CDC characterized 304 U.S. flu viruses during May 24–September 30, 2015, including 14 influenza A (H1N1)pdm09 viruses, 219 influenza A (H3N2) viruses, and 71 influenza B viruses. Virus characterization data will be updated weekly starting later in the season. All 14 influenza A (H1N1)pdm09 viruses were antigenically characterized as A/California/7/2009-like, the influenza A (H1N1) component of the 2015-2016 Northern Hemisphere. All 219 H3N2 viruses were genetically sequenced and all viruses belonged to genetic groups for which a majority of viruses antigenically characterized were similar to A/Switzerland/9715293/2013, the influenza A (H3N2) component of the 2015-2016 Northern Hemisphere vaccine. A subset of 95 H3N2 viruses also were antigenically characterized; 94 of 95 (99%) H3N2 viruses were A/Switzerland/9715293/2013-like by HI testing or neutralization testing. 44 (62%) of the 71 influenza B viruses collected and analyzed during this period belonged to the B/Yamagata lineage, and all were antigenically similar to the B/Phuket/3073/2013 virus, the influenza B component for both the 2015–16 Northern Hemisphere trivalent and quadrivalent vaccines. The remaining 27 (38%) influenza B viruses were antigenically characterized as B/Brisbane/60/2008-like, the recommended influenza B component of the 2015-16 Northern Hemisphere quadrivalent flu vaccine.

In addition, CDC has antigenically characterized three specimens (1 influenza A (H1N1)pdm09, 1 influenza A (H3) and 1 influenza B/Yamagata-lineage) collected in the U.S. since Oct. 1, 2015. All three were similar to the 2015-2016 Northern Hemisphere influenza vaccine components. Since Oct. 1, 2015, CDC has tested 13 influenza A (H3N2) for resistance to the neuraminidase inhibitors antiviral drugs. None of the tested viruses were found to be resistant to either oseltamivir, zanamivir, or peramivir. Antiviral resistance data will be updated weekly starting later in the season.

Source: CDC