Wave of H3N2 cases keeps US flu activity high

Though flu activity decreased slightly last week, a wave of H3N2 virus activity has led to severe illnesses across the country and four more children have died from the disease, according to this week's FluView report from the Centers for Disease Control and Prevention (CDC).

This is the second week in a row the CDC recorded more H3N2 cases that H1N1, the virus subtype that dominated the first part of the 2018-19 flu season.

"H3N2 viruses are typically associated with more severe illness in older adults, and flu vaccine may protect less well against H3N2 illness in older adults, making prompt treatment with flu antivirals in this age group especially important during the current period of H3N2 predominance," the CDC said today in a summary of the report.

Though seasonal flu vaccination is still recommended while influenza is circulating, the CDC said the use of antivirals is an important "second line of defense."

Four new kids' deaths, more hospitalizations

Last week brought with it 4 more pediatric deaths caused by flu, bringing the season's total to 68. At least two of the deaths were associated with an influenza A H3 virus, the CDC said.

Hospitalizations, which tend to increase later in the flu season, rose again this week, to 41.3 laboratory-confirmed influenza-associated hospitalizations per 100,000 population. The previous week saw a hospitalization rate of 36.6 per 100,000 population.

The highest hospitalization rate is among adults 65 years and older (123.9 hospitalizations per 100,000 population). The vast majority of hospitalizations (95.6%) were associated with influenza A virus, and 3.6% were connected to influenza B virus.

Overall, influenza A still dominates the season, representing 97.3 % of lab-tested positive samples. Of those, 38.7% are H1N1, and 61.3% are H3N2. Seven out of 10 US geographical regions are now reporting more H3N2 than H1N1 activity.

ILI down slightly

As in the recent previous weeks, the influenza-like illness (ILI) rate dropped to 4.5%, down from 5.0% and 4.7% in the previous 2 weeks, but it remained well above the national baseline of 2.2%.

This week the number of states experiencing high ILI activity decreased to 30 from 32, and 11 states experienced moderate ILI activity. New York City, the District of Columbia and five states experienced low ILI activity, while Puerto Rico and four states experienced minimal ILI activity.

Forty-six states and Puerto Rico reported widespread activity, down from 48 states the previous week.

See also:

Mar 15 CDC FluView

Mar 15 CDC FluView summary

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