Adult

Influenza treatment

  • Patients with suspected influenza should be isolated and respiratory precautions commenced – see here for advice.
  • If potential Avian Influenza (e.g. History of working with poultry, travel to USA, SE or South Asia), Discuss urgently with Micro/ID; see Triage of HCID.
  • The RECOVERY trial includes patients with influenza. To contact the RECOVERY research team use emergency.research@oxnet.nhs.uk or ext 22003. When prescribing for patients in the trial use the RECOVERY trial PowerPlan on EPR.

Eligibility for treatment

Patient group

Recommendation

 

Non -severe influenza illness (most healthy adults)

 

 

Do not treat

 

Severe influenza: evidence of complications directly resulting from influenza

  • Sepsis
  • Multiorgan failure
  • Signs/symptoms of pneumonia 
  • Encephalopathy
  • Significant exacerbation of an underlying chronic disease (e.g. COPD)

If within 48 hours symptom onset: Treat

If 2-5 days after symptom onset: can discuss starting treatment Micro/ID

More than 5 days after symptom onset: Do not treat

At risk of severe influenza:

  • Neurological, hepatic, renal, pulmonary and chronic cardiac disease
  • Diabetes mellitus
  • Potential immunosuppression*
  • Age over 65 years
  • Pregnancy (including up to 2 weeks post-partum)
  • Morbid obesity (BMI 40 or more)

If within 48 hours symptom onset: Treat

If 2-5 days after symptom onset: can discuss starting treatment with Micro/ID

More than 5 days after symptom onset: Do not treat

*see NICE TA 168  includes:-

  • primary immunodeficiency,
  • current or recent (within 6 months) chemotherapy or radiotherapy for malignancy,
  • solid organ transplant recipient on immunosuppressive therapy,
  • Bone marrow transplant recipient currently receiving immunosuppressive treatment or within 12 months of receiving immunosuppression,
  • Patients with current Graft vs host disease (GVHD), 
  • patients currently receiving high dose systemic corticosteroids (equivalent to 40 mg or more prednisolone per day for more than 1 week in an adult, or 2mg/kg/day or more for 1 week or longer in a child), and for at least 3 months after treatment has stopped
  • people living with HIV with severe immunosuppression (CD4<200/μl or <15% of total lymphocytes in an adult or child over 5; CD4< 500/μl or <15% of total lymphocytes in a child aged 1 to 5; expert clinical opinion in a child aged under 1)
  • patients currently or recently (within 6 months) on other types of highly immunosuppressive therapy or where the patient’s specialist regards them as severely immunosuppressed
     

 All use of antivirals must be as per UKHSA guidance on use of antiviral agents for the treatment and prophylaxis of seasonal influenzahttps://www.gov.uk/government/publications/influenza-treatment-and-prophylaxis-using-anti-viral-agents. Any use outside of this should be discussed with Micro/ID.

Drug Treatment

Non-severe influenza (and no risk factors for severe): No treatment (no evidence of benefit).

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Non-severe influenza, at risk of severe influenza or influenza complications:

Treatment of influenza in at risk and severely immunosuppressed patients should be started promptly when influenza is suspected rather than waiting for positive test results. After 5 days of symptoms, evidence of efficacy is less clear (discuss with Micro/ID)

  • First line treatment:

oseltamivir 75mg po bd for 5 days (10 days for immunosuppressed patients)

    • For dosing in adult patients 40kg or less: 60mg po bd for 5 days (10 days for immunosuppressed patients)
    • For dosing in renal impairment see oseltamivir drug monograph
  • Second line treatment:

Zanamivir  inhaled (diskhaler) 10mg (2 puffs) bd 

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Severe influenza: 

  • First line treatment:

oseltamivir 75mg po bd for 5 days (10 days for immunosuppressed patients)

    • For dosing in adult patients 40kg or less: 60mg po bd for 5 days (10 days for immunosuppressed patients)
    • For dosing in renal impairment see oseltamivir drug monograph

 

  • Second line treatment:

Zanamivir  inhaled (diskhaler) 10mg (2 puffs) bd for 5 days (10 days for immunosuppressed patients)

 

  • Third line treatment: 
    • poor clinical response to oseltamivir or concern about potential oseltamivir resistance (e.g. A [H1N1] pdm09) or unable to have inhaled zanamavir
    • always discuss with Micro/ID

Options include:

Zanamivir  IV (600mg bd iv) for 5 days (10 days for immunosuppressed patients)

  • For IV dosing in renal impairment see Zanamivir drug monograph

Or, Baloxavir (Marboxil) [Micro ID approval essential]

  • body weight over 80kg:, 80mg po, single dose (in addition to oseltamivir, as above)
  • body weight 20-79kg: 40mg po, single dose (in addition to oseltamivir, as above)

 

Editorial Information

Last reviewed: 18 Nov 2025