CDC FluView Week Week 9: Influenza Activity Showing Signs Of Increasing Again

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 For the past few weeks there have been subtle signs that influenza activity - which peaked in late December and fell sharply in January (see chart below) - might be trying to stage a bit of a comeback. In CDC FluView Week 6 we saw a small uptick in activity. 

While influenza rares are still well below the national baseline, this week several states have reported significant increases in activity. The percentage of influenza-positive lab samples has increased from 4.5% last week, to 5.8% this week, and visits to healthcare providers for respiratory complaints have increased slightly. 

The key points from today's CDC FluView follow:

Key Points

• Influenza activity is increasing in most of the country.
• The highest influenza percent positivity levels were seen in states in the central and south-central regions of the country.
• The majority of influenza viruses detected are A(H3N2). H3N2 viruses identified so far this season are genetically closely related to the vaccine virus. Antigenic data show that the majority of the H3N2 viruses characterized are antigenically different from the vaccine reference viruses. While the number of B/Victoria viruses circulating this season is small, the majority of the B/Victoria viruses characterized are antigenically similar to the vaccine reference virus.
• The percentage of outpatient visits due to respiratory illness increased slightly this week but is still below baseline. Influenza is contributing to levels of respiratory illness, but other respiratory viruses are also circulating. The relative contribution of influenza varies by location.
• The number of hospital admissions reported to HHS Protect has increased each week for the past five weeks.
• The cumulative hospitalization rate in the FluSurv-NET system is higher than the rate for the entire 2020-2021 season, but lower than the rate seen at this time during the four seasons preceding the COVID-19 pandemic.
• Two influenza-associated pediatric deaths were reported this week. There have been 10 pediatric deaths reported this season.
• CDC estimates that, so far this season, there have been at least 2.7 million flu illnesses, 26,000 hospitalizations, and 1,500 deaths from flu.
• An annual flu vaccine is the best way to protect against flu. Vaccination can prevent serious outcomes in people who get vaccinated but still get sick. CDC continues to recommend that everyone ages 6 months and older get a flu vaccine as long as flu activity continues.
• Flu vaccines are available at many different locations, including pharmacies and health departments. Visit www.vaccines.gov to find a flu vaccine near you.
• There are also flu antiviral drugs that can be used to treat flu illness.

While this has been a relatively mild flu season thus far, it has likely claimed somewhere around 1,500 lives, including those of 10 children.  With fewer people taking precautions for COVID, and a low level of community immunity, further increases in flu activity are possible in the weeks ahead. 

Despite the disappointing performance against H3N2 reported in yesterday's MMWR: Interim Estimates of 2021–22 Seasonal Influenza Vaccine Effectiveness, this year's flu shot may still provide protection against H1N1 and/or Influenza B should they make an appearance later this spring.  

While this latest uptick in flu activity may be short-lived, late-season - or even summer - flu outbreaks are not unheard of.  The only thing predictable about flu is its unpredictability.