#13,967
On the heels of yesterday's CDC HAN Advisory (see HAN #0418: Influenza Season Continues with an Increase in Influenza A(H3N2) Activity) we have the latest (week 12) FluView report which shows the level of flu activity remains elevated, but it has dropped slightly over last week.
This year's flu season, which likely has several more weeks to go, began in mid-December, and is turning into one of the longest in recent memory.
While the winter of 2018 started out with a relatively mild H1N1 virus, an emerging clade (3C.3a) of the H3N2 strain began to make a move in early February, reinvigorating this year's influenza season.
At the start of the flu season (Week 44) Clade 3C.3a comprised only 4% of H3N2 viruses characterized, but today makes up roughly 90% of the H3 viruses in the country. This upstart clade is, unfortunately, less well inhibited by this year's vaccine.
This recent rise led to a 30 day delay in the selection of the H3N2 component for next fall's Northern Hemisphere flu vaccine, which was finally announced a week ago (see WHO Selects Fall H3N2 Flu Shot Component: Clade 3C.3a).
As a result of this mid-season surge of H3N2, the CDC's 2018-2019 U.S. Flu Season: Preliminary Burden Estimates are slowly inching up into the moderately severe range (see graphic at top of blog).
Some excerpts from today's FluView report follow:
2018-2019 Influenza Season Week 12 ending March 23, 2019
All data are preliminary and may change as more reports are received.An overview of the CDC influenza surveillance system, including methodology and detailed descriptions of each data component, is available at http://www.cdc.gov/flu/weekly/overview.htm.Synopsis:
Influenza activity decreased but remains elevated in the United States. Influenza A(H1N1)pdm09 viruses predominated from October to mid-February and influenza A(H3N2) viruses have been more commonly identified since late February. Small numbers of influenza B viruses have also been reported. Below is a summary of the key influenza indicators for the week ending March 23, 2019
- Viral Surveillance:The percentage of respiratory specimens testing positive for influenza viruses in clinical laboratories decreased. Nationally, during the most recent three weeks, influenza A(H3) viruses were reported more frequently than influenza A(H1N1)pdm09 viruses and in all 10 HHS Regions.
- Virus Characterization:The majority of influenza viruses characterized antigenically are similar to the cell-grown reference viruses representing the 2018–2019 Northern Hemisphere influenza vaccine viruses. However, an increasing proportion of influenza A(H3N2) viruses are antigenically distinguishable from A/Singapore/INFIMH-16-0019/2016 (3C.2a1), a cell-propagated reference virus representing the A(H3N2) component of 2018-19 Northern Hemisphere influenza vaccines.
- Antiviral Resistance:The vast majority of influenza viruses tested (>99%) show susceptibility to oseltamivir and peramivir. All influenza viruses tested showed susceptibility to zanamivir.
- Influenza-like Illness Surveillance:The proportion of outpatient visits for influenza-like illness (ILI) decreased to 3.8%, and remains above the national baseline of 2.2%. All 10 regions reported ILI at or above their region-specific baseline level.
- ILI State Activity Indictor Map: 20 states experienced high ILI activity; Puerto Rico and 13 states experienced moderate ILI activity; New York City, the District of Columbia and seven states experienced low ILI activity; 10 states experienced minimal ILI activity; and the U.S. Virgin Islands had insufficient data.
- Geographic Spread of Influenza: The geographic spread of influenza in Puerto Rico and 34 states was reported as widespread; 14 states reported regional activity; the District of Columbia and two states reported local activity; the U.S. Virgin Islands reported sporadic activity; and Guam did not report.
- Influenza-associated Hospitalizations A cumulative rate of 52.5 laboratory-confirmed influenza-associated hospitalizations per 100,000 population was reported. The highest hospitalization rate is among adults 65 years and older (167.0 hospitalizations per 100,000 population).
- Pneumonia and Influenza Mortality: The proportion of deaths attributed to pneumonia and influenza (P&I) was above the system-specific epidemic threshold in the National Center for Health Statistics (NCHS) Mortality Surveillance System.
- Influenza-associated Pediatric Deaths: One influenza-associated pediatric death was reported to CDC during week 12.
(Continue . . . )
While it is late in the season, if you haven't gotten a flu shot, you should seriously consider doing so, even if it is less effective against this new clade. You should continue to practice good flu hygiene (covering coughs, washing/ sanitizing hands, and staying home if you are sick), as well.
And if you get sick, call your doctor. Early treatment with antivirals can shorten your illness, and for some patients, be life saving.
