Flu declines, but hospitalizations are still high

Influenza is on the retreat, but several indicators still show high activity in many parts of the country, according to the latest data compiled in the Centers for Disease Control and Prevention's (CDC's) weekly FluView report.

The percentage of outpatient visits for influenza-like illnesses (ILI) is down to 3.3%, significantly lower than the season's mid-February peak of 7.5%. That indicator has been at or above the national baseline of 2.2% for 16 weeks so far this season.

A total of 26 states plus Puerto Rico reported widespread flu activity and 12 states (Alaska, Arizona, Georgia, Kansas, Kentucky, Missouri, Nebraska, New Jersey, New Mexico, South Carolina, Virginia, and Wyoming) continue to experience high ILI activity.

Hospitalization rates still on the rise

Similar to last week, hospitalization rates rose slightly to a cumulative rate of 89.9 laboratory-confirmed influenza-associated hospitalizations per 100,000 population. In the previous week, that rate was 86.3 per 100,000 population.

The hospitalization rate of Americans over 65 increased to 386.2 per 100,000 population, up from the previous week’s 370.6 per 100,000 population. The rate for adults aged 50 to 64 was 97.3 per 100,000 population, and children aged 0 to 4 years were hospitalized at a rate of 64.9 per 100,000 population.

Although influenza A and B strains are now cocirculating nearly equally, the vast majority of hospitalizations (79.0%) were associated with influenza A virus. Among those with influenza A subtype information, 85.2% were H3N2, the dominant strain of the 2017-2018 flu season.

Unfortunately, the CDC also was notified of nine more pediatric deaths from influenza in the last week, bringing the season's total to 128.

Flu B outpaces A; vaccination still useful

Among all positive lab specimens reported to the CDC in the last week, 46.5% were influenza A viruses and 53.5% were influenza B viruses, which is typical for the end of a flu season. H3N2 remains the dominant A subtype, with 71.5% of samples. Over half of all influenza B samples (54.2%) are of the Yamagata lineage.

The CDC said it expects flu activity to remain elevated for several more weeks. "CDC routinely recommends influenza vaccination for all persons 6 months of age and older as long as flu viruses are circulating," the CDC said in a FluView summary.

"Early vaccine effectiveness (VE) estimates through February 3, 2018, show that flu vaccine has reduced the risk of having to go to the doctor due to flu by 36% overall. VE against H3N2 viruses was 25%. VE against H1N1 67% and VE against B viruses was 42%."

See also:

Mar 16 CDC FluView

Mar 16 CDC summary

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