Antiviral post-exposure influenza prophylaxis

• post-exposure prophylaxis (PEP) with antiviral agents (oseltamivir or zanamivir) should be considered during circulating influenza seasons for exposed individuals who are at risk of severe influenza complications (1,2)
• PEP should be initiated as early as possible following exposure (within 48 hours of contact for oseltamivir and within 36 hours for inhaled zanamivir) (1)
• updated UK Health Security Agency (UKHSA) guidance removes the requirement for non-vaccination, allowing PEP to be offered to severely immunosuppressed individuals regardless of vaccination status (2)

Indications and triage criteria

Primary care prescribing criteria

• offer PEP to exposed individuals during the circulating influenza season if all of the following criteria are met:
  • national surveillance indicates seasonal influenza is circulating in the community
  • the individual has had close contact with a person with suspected or confirmed influenza-like illness (e.g. household or residential setting contact)
  • the individual is in an at-risk clinical group or is severely immunosuppressed (1,2)
  • PEP can be initiated within 48 hours of contact for oseltamivir or within 36 hours for inhaled zanamivir

At-risk clinical groups for influenza

• adults aged 65 years or older
• chronic respiratory disease (e.g. asthma requiring continuous or frequent use of systemic steroids, COPD, bronchiectasis, cystic fibrosis)
• chronic heart disease (e.g. congenital heart disease, heart failure, ischaemic heart disease)
• chronic kidney disease (e.g. stage 3, 4 or 5 CKD, haemodialysis, peritoneal dialysis)
• chronic liver disease (e.g. cirrhosis, chronic hepatitis)
• chronic neurological disease (e.g. stroke, TIA, motor neurone disease, severe learning disability)
• diabetes mellitus (including type 1 and type 2 diabetes requiring medication)
• morbid obesity (BMI ≥40 kg/m²)
• pregnancy (including up to 2 weeks post-partum)
• children under 6 months of age
• immunosuppression (including patients with disease- or treatment-induced immunocompromise)

Severe immunosuppression definition

• severe primary immunodeficiency
• active or recent chemotherapy or radiotherapy for malignancy (within 6 months)
• solid organ or bone marrow transplant recipients on active immunosuppressive therapy
• high-dose systemic corticosteroid therapy (≥40 mg prednisolone daily for >1 week in adults)
• advanced HIV infection (CD4 <200/µL)

Exposure management by risk profile

• otherwise healthy individuals: PEP is not routinely recommended; manage with general infection prevention and hygiene measures, self-isolation advice, and safety-netting regarding severe symptoms
• individuals with standard risk factors: offer PEP (or alternatively institute close clinical monitoring with prompt initiation of full-dose antiviral treatment if symptoms develop) (1)
• severely immunosuppressed individuals: offer PEP following exposure regardless of seasonal influenza vaccination status due to reduced vaccine response and high risk of severe complications (2)

Prescribing pathways and regimens

Standard prophylaxis dosing

• oseltamivir (oral neuraminidase inhibitor): standard first-line choice for adults and children (1)
  • adult dose: 75 mg once daily orally for 10 days
  • initiation window: start within 48 hours of last contact
• zanamivir (inhaled neuraminidase inhibitor): alternative first-line option for patients aged 5 years and over where oseltamivir is unsuitable, poorly tolerated, or where oseltamivir resistance is suspected
  • adult dose: 10 mg (2 inhalations) once daily for 10 days
  • initiation window: start within 36 hours of last contact
  • note: avoid inhaled zanamivir in severe asthma or severe COPD due to risk of acute bronchospasm

Special scenarios and outbreak control

• pregnancy and breastfeeding:
  • oral oseltamivir (75 mg once daily for 10 days) remains the preferred choice at any stage of pregnancy or post-partum due to established safety data (2)
• institutional exposures:
  • in care homes or closed healthcare settings with continuous exposure, extended prophylaxis (up to 14 days or until 7 days after the last case) may be advised under local Health Protection Team (HPT) guidance

References:

1. National Institute for Health and Care Excellence (NICE). Oseltamivir, amantadine and zanamivir for the prophylaxis of influenza. NICE Technology Appraisal [TA158]. 2008.
2. UK Health Security Agency (UKHSA). Guidance on use of antiviral agents for the treatment and prophylaxis of seasonal influenza. UKHSA Public Health Guidance. Updated October 2026.