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The Centers for Disease Control and Prevention (CDC) is anticipating an increase in influenza illness this winter, and both influenza A(H3N2) and B viruses are cocirculating in some parts of the country. While influenza activity is still low in Idaho and overall nationally, a recent increase of influenza A(H3N2) viruses has been detected primarily in young adults in outbreaks at colleges and universities in several states. As SARS- CoV-2 continues to circulate in the United States, illnesses associated with both viruses might stress healthcare systems.
Recommendations for Clinicians
- Recommend and offer influenza vaccination for all eligible people aged six months and older
Anyone who has not received an influenza vaccine this season should be offered vaccine now. For 2021-2022, CDC recommends using any licensed, age-appropriate influenza vaccine this season. Both influenza and COVID-19 vaccines can be administered during the same visit, without regard to timing. If a patient is due for both vaccines, both vaccines should be offered at the same visit. Information on influenza vaccination is available in the current ACIP recommendations: https://www.cdc.gov/flu/professionals/acip/summary/summary-recommendations.htm - Treat patients with suspected or confirmed influenza who meet clinical criteria
with influenza antivirals
Antiviral treatment should be started as soon as possible for patients with suspected or confirmed influenza who are:- Hospitalized
- Outpatients at increased risk for complications
- Outpatients with progressive disease
- Start antiviral treatment within two days after the beginning of illness when
possible. Antiviral treatment started after 48 hours of symptom onset may still
offer some benefit. - For people co-infected with influenza and SARS-CoV-2 viruses, influenza
antivirals can be given for influenza illness which may benefit the patient’s
outcome. - Decisions about starting antiviral treatment should not wait for laboratory
confirmation of influenza. However, COVID-19 should be excluded with a rapid
diagnostic assay if one is available.
- Use of influenza antivirals for post-exposure prophylaxis (PEP)
Both oseltamivir and baloxavir are FDA-approved for influenza PEP. CDC recommends using clinical judgment for antiviral PEP for certain exposed non-ill close contacts of people with suspected or confirmed influenza. In the context of co-circulation with SARS-CoV-2, influenza antiviral PEP might be considered for people:
- With recent close contact with a person with influenza (e.g., roommates)
- Living in confined quarters (e.g., dormitories, shelters, prisons) with increasing
incidence of influenza - Who are at increased risk for severe illness from influenza
- Who have had recent close contact with a person with influenza and will be
traveling, which may reduce transmission during travel and to family members or
friends who may be at higher risk for influenza complications
The efficacy of PEP in reducing virus acquisition to uninfected household contacts is high for oseltamivir (68%-89%) and baloxavir (86%). A key difference between the drugs relates to the longer half-life of baloxavir (days) vs. the shorter half-life of oseltamivir (hours). For PEP, baloxavir can be administered as a single dose while oseltamivir requires daily dosing for seven days.
- Dosing: Treatment and prophylaxis (prevention) dosing is the same for baloxavir, but for oseltamivir, treatment dosing is twice daily, and prophylaxis is once daily.
- Timing: CDC recommends initiating PEP within 48 hours of contact with an influenza case. In general, PEP for oseltamivir should not be started >48 hours after exposure due to concerns about resistance with lower PEP dose in persons with active influenza.
- Duration: Antiviral medications are effective as PEP only if a person takes them the entire time they are around another person who has influenza.
Rates of oseltamivir and baloxavir resistance among circulating influenza A viruses remain low. However, additional monitoring is necessary, especially with baloxavir, which has had limited use compared to oseltamivir.
Information about antiviral treatment and PEP is available in the CDC Influenza Antiviral Medications: Summary for Clinicians: https://www.cdc.gov/flu/professionals/antivirals/summary-clinicians.htm
4. Influenza testing
The most accurate influenza tests (high sensitivity and specificity) are molecular assays. Molecular assays are recommended for hospitalized patients with suspected influenza. Because illness presentation may be similar, Idaho encourages the testing of samples simultaneously for both SARS
CoV-2 and influenza. Information about influenza virus testing is available from CDC:
- General information: https://www.cdc.gov/flu/professionals/diagnosis/index.htm
- Influenza testing when SARS-CoV-2 viruses are co-circulating: https://www.cdc.gov/flu/professionals/diagnosis/testing-guidance-for-
clinicians-hospitaized.htm
Virologic surveillance in Idaho:
The Idaho Bureau of Laboratories (IBL) uses the Influenza SARS-CoV-2 (Flu SC2) multiplex real time RT-PCR molecular assay to determine the presence and subtype of influenza in circulation and rule out SARS-CoV-2 as the cause of influenza-like illness (ILI). IBL will accept clinical samples from providers for Flu SC2 testing from symptomatic patients that test negative for SARS-CoV-2. IBL will also accept samples from influenza rapid-test negative individuals, where ILI is present and the suspicion for influenza is high; ruling out false negative rapid tests.
IBL is requesting clinical laboratories submit up to 5 representative influenza-positive specimens per week throughout the influenza season, to determine circulating subtypes in support of influenza virologic surveillance efforts in Idaho.
IBL Flu SC2 submission form: https://publicdocuments.dhw.idaho.gov/WebLink/DocView.aspx?id=2781&dbid=0&repo=PUBLIC-DOCUMENTS&cr=1
Additional Resources for Clinicians:
- Influenza in Idaho: https://flu.idaho.gov/
- Additional CDC Resources for Clinicians:
