Influenza Update

January 22, 2023


Influenza activity continues to decline in Wisconsin. Most detections (81%) have been A(H3N2). Other than influenza and SARS-CoV-2, we are seeing significant levels of rhinovirus/enterovirus, seasonal coronaviruses, and RSV.

Across the U.S. there were 453 (7.2%) influenza detections at public health laboratories, from the 6,315 specimens collected last week. Of detected viruses, 97.6% were influenza A and 2.4% were influenza B. Among influenza A viruses, 81.3% were H3 and 18.7% were H1. CDC has reported an excellent match between circulating and vaccine strains (H3: 94%; H1: 100%; B: 100%) for this season. As of 1/20/2022, CDC estimates that there have been at least 25 million illnesses, 270,000 hospitalizations, and 17,000 deaths from flu. The percentage of primary care patients with influenza-like illness (ILI) is 3.0% and has decreased. ILI activity is moderate or below for most of our states. Eighty-five pediatric deaths, due to influenza A (83) and influenza B (2), have been reported for the 2022-2023 season to date.  

Use of rapid testing at this time is reasonable at this time based on levels of circulating virus. RIDT(+) results for influenza B should continue to be confirmed using RT-PCR.

Antivirals need to be started with 48 hours of symptom onset to be effective against influenza.

Antivirals started after 48 hours may be effective for hospitalized patients with confirmed influenza.

            Note: there is a national shortage of oseltamivir. Local availability is variable.

Primary Care Snapshot

The most common viral causes of acute respiratory infections in Wisconsin primary care practices are influenza A, seasonal coronaviruses, and RSV. For the week ending January 14, 2023, 6.9% of 24,895 specimens tested across Wisconsin and compiled by the Wisconsin State Laboratory of Hygiene and clinical labs were positive for SARS-CoV-2. About 1.7% of primary care patients are presenting with acute diarrheal illness. The most commonly identified pathogens are Sapovirus and Norovirus.

Over the past 4 weeks the typical ARI case has been 38.2 years old. 61% of patients have been female. 60% of patients identified a sick contact 1-3 days before illness onset and they typically present to the clinic 4.4 days after illness onset. 35% of illnesses are characterized as mild, with 57% having moderate symptoms and 4% having severe symptoms.

Viruses in CirculationPercent* in statewide laboratory surveillancePercent** in primary care surveillance clinics
Influenza A28.653%
Influenza B0.00%
Seasonal Coronavirus***0.215%
*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

As of today, 669,676,070 global cases have been confirmed, with 6,799,126 reported deaths (Case Fatality Rate = 1.0%). There have been 102,193,036 laboratory-confirmed cases reported in the United States with 1,106,633 deaths (CFR = 1.1%). Closer to home, there have been 1,979,913 confirmed cases in Wisconsin, with 16,070 deaths (CFR = 0.8%). Please note that the CFRs reported here are crude and based only on laboratory confirmed cases.


Across the state, “community” levels of COVID-19 (based on rates of new cases, hospital admissions, and percent occupancy of staffed beds) are high in 2 counties, medium in 5 counties, and low in 65 counties. The 7-day average for patients hospitalized for COVID-19 in Wisconsin is 530 and a 7-day average of 76 (14%) 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 7.2 fewer new cases each day).

COVID-19 Vaccine

Across Wisconsin, 3,606,489 individuals (61.8% of the population) have completed their primary series of vaccine and 1,120,823 (19.2%) have received the updated (bivalent) booster. 

Across the US:

  • The overall cumulative rate for COVID-19 hospitalization across the U.S. is estimated at 1,317.8/100,000 (one admission for every 76 people).
  • The overall cumulative death rate for COVID-19 across the U.S. is 332.9/100,000 (one death for every 300 people).
  • 13.1% of all deaths during week 2 (January 8—14) 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 January 14, 2023. XBB.1.5 (49.1%), BQ.1.1 (26.9%), and BQ.1 (13.3%), are the dominant lineages; XBB is at 3.3% and BA.5 is at 2.0%.

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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