Influenza Update

Weekly Influenza Updates will begin in the Fall. Stay tuned for more information and use the CDC website for seasonal influenza updates.

March 23, 2023


Influenza activity has waned to very low levels in Wisconsin. Most detections have been A(H3N2) viruses. Other than influenza and SARS-CoV-2, we are seeing significant levels of seasonal coronaviruses, human metapneumovirus, and rhinovirus.

Across the U.S. there were 79 (1.3%) influenza detections at public health laboratories, from the 6,258 specimens collected last week. Of detected viruses, 73.4% were influenza A and 26.6% were influenza B.  Among influenza A viruses, 34.3% were H3 and 65.7% were H1. CDC has reported an excellent match between circulating and vaccine strains (H3: 93%; H1: 98%; B: 100%) for this season. As of 3/17/2023, CDC estimates that there have been at least 26 million illnesses, 290,000 hospitalizations, and 18,000 deaths from flu. The percentage of primary care patients with influenza-like illness (ILI) is 2.4% and is below baseline. ILI activity is low for almost all of our states. One hundred and thirty-two pediatric deaths, due to influenza A (129) and influenza B (3), have been reported for the 2022-2023 season to date.

Use of rapid influenza testing at this time is tenuous at this time based on low levels of circulating virus. RIDT(+) results should be confirmed using RT-PCR. Use of rapid COVID-19 testing is reasonable and positive results do not need confirmation.

Primary Care Snapshot

The most common viral causes of acute respiratory infections in Wisconsin primary care practices are seasonal coronaviruses. For the week ending March 11, 2023, 9.3% of 17,461 specimens tested across Wisconsin and compiled by the Wisconsin State Laboratory of Hygiene and clinical labs were positive for SARS-CoV-2. About 1.9% of primary care patients are presenting with acute diarrheal illness. The most commonly identified gastopathogen is Norovirus.

Over the past 4 weeks the typical ARI case has been 25.3 years old. 73% of patients have been female. 61% of patients identified a sick contact 1-3 days before illness onset and they typically present to the clinic 3.7 days after illness onset. 48% of illnesses are characterized as mild, with 39% having moderate symptoms and 9% having severe symptoms.

Viruses in CirculationPercent* in statewide laboratory surveillancePercent** in primary care surveillance clinics
Influenza A5.60%
Influenza B0.00%
Seasonal Coronavirus***0.147%
*estimate based on WSLH statewide data
** estimate based on primary care patients seen at five clinics in Dane County where COVID-19 patients are often deflected
*** includes HKU1, NL63, 229E and OC43

SARS-CoV-2 Cases

On March 10, 2023, Johns Hopkins University ceased updating their COVID-19 Dashboard. To me, this is a clear indication of our transition to endemicity. There have been 2,013,479 confirmed cases in Wisconsin, with 16,422 deaths (CFR = 0.8%).


Across the state, “community” levels of COVID-19 (based on rates of new cases, hospital admissions, and percent occupancy of staffed beds) are medium in 2 counties, and low in 70 counties. The 7-day average for patients hospitalized for COVID-19 in Wisconsin is 309 and a 7-day average of 47 (15%) requiring intensive care.

Wisconsin’s 14-day Trend

Over the past 14 days, there has been a decrease in the growth rate of new cases per day (average of 6.7 fewer new cases each day).


COVID-19 Vaccine

Across Wisconsin, 3,607,355 individuals (61.8% of the population) have completed their primary series of vaccine and 1,183,986 (20.3%) have received the updated (bivalent) booster.

Across the US:

  • The overall cumulative rate for COVID-19 hospitalization across the U.S. is estimated at 1,374.2/100,000 (one admission for every 73 people).
  • The overall cumulative death rate for COVID-19 across the U.S. is 337.4/100,000 (one death for every 296 people).
  • 8.6% of all deaths during week 10 (Mar. 5-11) were due to pneumonia, influenza, or COVID-19.
  • Variants: the national proportion comprised of Omicron variants was estimated to be 100% for the week ending March 18, 2023. XBB.1.5 (90.2%), BQ.1.1 (3.5%), and XBB (2.5%), are the dominant lineages; XBB.1.5.1 is at 2.2%.

Please refer to guidance provided by Wisconsin Department of Health Services, available at:

and by the U.S. Centers for Disease Control and Prevention, available at:

* The weekly influenza update is adapted from an email from Jon Temte, MD, PhD; Chair, Wisconsin Council on Immunization Practices; Professor, Department of Family Medicine and Community Health, University of Wisconsin School of Medicine and Public Health.

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