The Exchange

Commentary and Observations from
the Medical Front Lines

Upside Down: Influenza B Appears to be Waning While Influenza A is Increasing

Upside Down: Influenza B Appears to be Waning While Influenza A is Increasing

In a typical flu season, influenza A activity begins between November and January and fades after a few months. Concurrently, influenza B occurs with increasing frequency until it fades in the spring. This year's flu season has been backwards; and it might be even more unusual in that influenza B may have a later resurgence, resulting in a triple peaking of B, A, and then B again.

This has been a particularly dangerous flu season for the pediatric population with 136 deaths as of this postingthe second highest number of flu-related pediatric deaths in history. Additional CDC statistics on the 2019-2020 flu season are striking:


  • Outpatient influenza-like illness and clinical laboratory data remain elevated, though have decreased slightly this week. The overall decrease in the percentage of specimens testing positive for influenza was due to a decrease in the percentage of specimens testing positive for influenza B. The percentage of specimens testing positive for influenza A continued to increase.
  • Overall, hospitalization rates remain similar to previous flu seasons during this time, but rates among children and young adults are elevated compared to recent seasons.
  • Thus far, pneumonia and influenza mortality has been low; however, the 136 reported pediatric deaths is higher than nearly all previous seasons.
  • It is estimated that there have been at least 34 million flu illnesses, 350,000 hospitalizations, and 20,000 deaths in the US from flu so far this season.
  • This past month, interim estimates of the 2019-2020 flu vaccine effectiveness were released. Encouragingly, flu vaccines are helping to reduce flu-related doctor's visits by 45% overall and by 55% in the pediatric population.

With that last note in mind, remember that there is still time to giveand getthe flu shot, for children, adolescents, and adults.

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