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This Guidelines summary covers Public Health England (PHE) guidance on the use of antiviral agents for prophylaxis in people who may have been exposed to seasonal influenza. You can see our summary of PHE advice on antiviral treatment of people who have suspected or confirmed seasonal influenza here and 10 frequently asked questions can be found here.

Post exposure prophylaxis

  • NICE has provided guidance stating that oseltamivir and zanamivir may be used for prophylaxis of persons in at risk groups (see definitions) following exposure to a person in the same household or residential setting with influenza-like illness when influenza is circulating in the community
  • As per NICE guidance, prophylaxis should be issued if the contact is not adequately protected by vaccination, that is:
    • the vaccination is not well matched to the circulating strain, or
    • there has been less than 14 days between vaccination and date of first contact with influenza
  • In addition, the guidance also states that—if the individual has been exposed as part of localised outbreaks in care homes, antiviral prophylaxis may be given regardless of vaccination status. For further guidance on care home outbreaks, see PHE guidance on the management of outbreaks of influenza like illness (ILI) in care homes
  • For further information on which contacts of a case of influenza should receive prophylaxis, refer to guidance from NICE. Special considerations may apply to localised incident situations; specialist advice in relation to incidents such as influenza outbreaks, may be sought from local health protection teams
  • Prophylaxis is normally not considered in at-risk groups who have been vaccinated against seasonal influenza at least 14 days before exposure, with the above exceptions. Clinicians should note however, that such use is outside the NICE guidance recommendations and would therefore be a matter for individual clinical judgement
  • Inhaled zanamivir is not licensed for children under 5 years old, and is unlikely to be an effective delivery route in these patients. Some other patients, such as those with severe underlying respiratory disease or impaired cognition, may also be unable to use the Diskhaler® effectively. Severely immunosuppressed children under 5 years and all other severely immunosuppressed patients who cannot use the Diskhaler® and require prophylaxis after exposure to currently circulating antiviral sensitive strains of influenza should receive oral oseltamivir, with advice to seek immediate medical attention if symptoms develop subsequently
  • Severely immunocompromised patients who are unable to use the Diskhaler®, including severely immunosuppressed children aged less than 5 years, and who are exposed to suspected or confirmed oseltamivir resistant influenza should be discussed with a specialist. These individuals should receive close clinical monitoring following exposure with arrangements to receive prompt treatment following onset of ILI symptoms
Table 1: Selection of antivirals for post-exposure prophylaxis
 If identified strain in index case or dominant circulating strain is lower risk for oseltamivir resistance e.g. influenza A (H3N2), influenza BIf identified strain in index case or dominant circulating strain is known to higher risk for oseltamivir resistance e.g. influenza A (H1N1)pdm09Exposed to suspected or confirmed oseltamivir resistant influenza

Previously healthy (excluding pregnant women)

No prophylaxis

No prophylaxis

No prophylaxis

At risk of complicated influenza (including pregnant women but excluding severely immunosuppressed patients and excluding children under 5 years)

Oseltamivir p.o. once daily for 10 days, if therapy can be started within 48 hours of exposure; or after 48 hours on specialist advice only

Oseltamivir p.o. once daily for 10 days, if therapy can be started within 48 hours of exposure; or after 48 hours on specialist advice only

Zanamivir INH once daily for 10 days, if therapy can be started within 36 hours of exposure; or after 36 hours on specialist advice only

Severely immunosuppressed patients (excluding children under 5 years)

Oseltamivir p.o. once daily for 10 days, if therapy can be started within 48 hours of exposure; or after 48 hours on specialist advice only

Zanamivir INH once daily for 10 days, if therapy can be started within 36 hours of exposure; or after 36 hours on specialist advice only. If unable to administer zanamivir INH, oseltamivir p.o. once daily for 10 days, if therapy can be started within 48 hours of exposure; or after 48 hours on specialist advice only

Zanamivir INH once daily for 10 days, only if therapy can be started within 36 hours of exposure; or after 36 hours on specialist advice only. If unable to administer zanamivir INH, monitor closely and begin treatment promptly if ILI symptoms develop

Children under 5 years in at risk groups including severely immunocompromised children

Oseltamivir p.o. once daily for 10 days,  if therapy can be started within 48 hours of exposure; or after 48 hours on specialist advice only

Oseltamivir p.o. once daily for 10 days,  if therapy can be started within 48 hours of exposure; or after 48 hours on specialist advice only

Monitor closely and begin treatment promptly if ILI symptoms develop

p.o.=by mouth; INH=inhaled.

Note: Commencing prophylaxis with oseltamivir later than 48 hours after exposure, or with zanamivir, later than 36 hours after exposure is an off-label use. Specialist advice referred to in the table above may be obtained from a local infection specialist such as a virologist

  • Specialist advice is available from local health protection teams and public health virologists for prophylaxis in healthcare settings where repeated or ongoing exposure is suspected
  • An alternative to prophylaxis in some clinical settings may be to monitor persons exposed to an influenza case and start antiviral treatment promptly when symptoms of influenza start. It is recommended that such an arrangement is undertaken only when:
    • the patient (or their carer) has been provided with information on symptoms prompting antiviral use, potential adverse events, and has decided to take antiviral medicines for treatment rather than prophylaxis and
    • the clinician has made arrangements in advance with a relevant pharmacy for the patient to promptly receive and start antiviral treatment within 48 hours of symptom onset (or 36 hours for zanamivir treatment in children)

Antiviral dosage and schedules

Table 2: Prophylaxis dosage


Premature (less than 36 weeks post conceptual age)

0 to 12 months (36 weeks post conceptual age or greater)

>1–12 years: dose according to weight below 

Adults (13 years and over)[B]

≤15 kg

>15–23 kg

>23–40 kg

>40 kg

Oseltamivir p.o. (prophylaxis course: 10 days)

See below[A]

3 mg/kg o.d.

30 mg o.d.

45 mg o.d.

60 mg o.d. 

75 mg o.d.

75 mg o.d.

Zanamivir INH (prophylaxis course: 10 days)

Not licensed for children <5 years old.
Adults and children ≥5 years: 10 mg o.d.

10 mg o.d.

p.o.=by mouth; o.d.=once daily; INH=inhaled.

[A] Although it may be possible to provide half the treatment frequency, each day for 10 days, there is currently no publicly available dosing information for oseltamivir prophylaxis in pre-term infants, and so is outside the product licence

[B] If a person in this age group weighs 40 kg or less, it is suggested that the >23–40 kg dose for those aged >1–12 years is used.       

Dosing in patients with renal dysfunction

  • General considerations about prescribing for renal impairment discussed in the treatment section may also be applicable when prescribing for prophylaxis, except that the dosage of oseltamivir in Table 3 (below) should be used
Table 3: Recommended oseltamivir prophylaxis dosing in relation to renal function (adults and those aged 13 years or over)
CrCl (ml/min)Oseltamivir p.o. prophylaxis for 10 days

>60 ml/min[A]

75 mg o.d.

31–60 ml/min[A]

30 mg o.d.

11–30 ml/min[A]

30 mg every 48 hours


30 mg once, repeated after 7 days

Haemo-dialysis (HD)[B]

30 mg once and then 30 mg after every second HD session

Continuous Ambulatory Peritoneal Dialysis[A] (refer to Summary of Product Characteristics for advice in relation to automated peritoneal dialysis [APD] mode)

30 mg once, repeated after 7 days 

Haemo(dia)filtration[B] –1.8 l/hr exchange rate

30 mg every 48 hours

1.9–3.6 l/hr exchange rate

30 mg o.d.

>3.6 l/hr exchange rate

75 mg o.d.

CrCl=creatinine clearance; p.o.=by mouth; o.d.=once daily

[A] Summary of product characteristics updated February 2019.

[B] The recommendations for haemo-dialysis, haemo(dia)filtration and established renal failure are based on expert opinion.

  • Note: It is acknowledged that the some of the advice for dosing in renal impairment presented here may differ to the renal drug handbook; however, the dosage information presented above is consistent with the summary of product characteristics provided by the manufacturer, at the time of writing

Prescribing in primary care 

  • GPs may only prescribe antiviral medicines for the prophylaxis and treatment of influenza under the General Medical Services (GMS) regulations when the Chief Medical Officer (CMO) has confirmed that influenza is circulating in the community. The CMO announcement is issued to the NHS through the Central Alerting System (CAS)
  • GPs have the discretion to prescribe antiviral medicines for people who are not in the specified at-risk groups but who are considered to be at risk of complications if not treated with an antiviral medicine


  • Uncomplicated influenza: influenza presenting with fever, coryza, generalised symptoms (headache, malaise, myalgia, arthralgia) and sometimes gastrointestinal symptoms, but without any features of complicated influenza
  • Complicated influenza: influenza requiring hospital admission and/or with symptoms and signs of lower respiratory tract infection (hypoxaemia, dyspnoea, lung infiltrate), central nervous system involvement and/or a significant exacerbation of an underlying medical condition
  • Risk factors for complicated influenza:
    • neurological, hepatic, renal, pulmonary and chronic cardiac disease
    • diabetes mellitus
    • severe immunosuppression
    • age over 65 years
    • pregnancy (including up to two weeks post partum)
    • children under 6 months of age
    • morbid obesity (BMI ≥40)
  • For full details refer to Immunisation against infectious disease, known as the Green Book
  • Severe immunosuppression: Examples of severe immunosuppression relevant to this guidance are given below. Degrees of immunosuppression are difficult to quantify and individual variation exists, therefore this list is not comprehensive:
    • severe primary immunodeficiency
    • current or recent (within 6 months) chemotherapy or radiotherapy for malignancy
    • solid organ transplant recipients on immunosuppressive therapy
    • bone marrow transplant recipients currently receiving immunosuppressive treatment, or within 12 months of receiving immunosuppression
    • patients with current graft-versus-host disease
    • patients currently receiving high dose systemic corticosteroids (equivalent to ≥40 mg prednisolone per day for >1 week in an adult, or ≥2 mg/kg/day for ≥1 week in a child), and for at least 3 months after treatment has stopped
    • HIV infected patients with severe immunosuppression (CD4 <200/mcl or <15% of total lymphocytes in an adult or child over 5 years; CD4 <500/mcl or <15% of total lymphocytes in a child aged 1–5; 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


full guideline available from…


Public Health England. PHE guidance on use of antiviral agents for the treatment and prophylaxis of seasonal influenza. January 2019.
Contains public sector information licensed under the Open Government Licence v3.0.

First included: November 2017.

Last updated: September 2019. 

PHE seasonal influenza antiviral treatment guideline