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After last week's brief downturn in ILI reports (see chart above), the number of office visits for Influenza-Like Illness nationwide rose significantly for Epi week 50, which ended on December 14th. This makes the 6th week in a row with influenza activity running above the baseline level.
Unusually, Influenza B continues to lead the way, followed by A/H1N1. So far, H3N2 - which has dominated the past several U.S. flu seasons - is in the back of the pack.
While all age groups are susceptible to all of the flu types in circulation, influenza B typically hits kids hardest, A/H3N2 tends to impact adults over 65 the most, while A/H1N1 typically has its biggest impact on younger adults.
So far this flu season, 19 pediatric deaths have been reported, with 9 of those reported over the past week (see chart below). While pediatric flu deaths are a reportable event, the numbers we get are likely an under count. The CDC reports:
A total of 19 influenza-associated pediatric deaths occurring during the 2019-2020 season have been reported to CDC.
- Thirteen deaths were associated with influenza B viruses. Five of these had the lineage determined and all were B/Victoria viruses.
- Six deaths were associated with influenza A viruses. Four of these had subtyping performed and all were A(H1N1)pdm09 viruses.
The CDC offers the following Key Points in this week's update:
Key Points
- The 2019-2020 season is underway; all regions of the country are seeing elevated levels of flu-like illness.
- Activity is being caused mostly by influenza B/Victoria viruses, which is unusual for this time of year. A(H1N1) viruses are the next most common and are increasing in proportion relative to other influenza viruses in some regions.
- CDC estimates that so far this season there have been at least 3.7 million flu illnesses, 32,000 hospitalizations and 1,800 deaths from flu.
- It’s not too late to get vaccinated. Flu vaccination is always the best way to prevent flu and its potentially serious complications.
- Antiviral medications are an important adjunct to flu vaccine in the control of influenza. Almost all (>99%) of the influenza viruses tested this season are susceptible to the four FDA-approved influenza antiviral medications recommended for use in the U.S. this season.
While it is possible we'll continue to see influenza B dominate for the rest of the flu season, it is also possible that H1N1 (or even H3N2) will mount a late season upset. The good news is the H1N1 component is likely the most effective in this year's vaccine, which will hopefully mitigate its impact.
While it is still early days, the CDC estimates the following burden from this year's flu season.
As always this time of year, now is the time to rigorously practice good flu hygiene. Stay home if you are sick, avoid crowds, wash your hands frequently, and cover your coughs and sneezes.
It is also not too late to get a flu shot.If you do get sick, call your doctor. Early treatment with antivirals can shorten your illness, and for some patients, can be life saving.
If flu does visit your household this winter, the CDC has a 21 page (PDF) Home Flu Treatment Guide, which covers everything from knowing the symptoms of flu, to setting up (and cleaning) a sick room, to when it is time to seek medical help.
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