Previous changes

November 2025 — minor update. Updated in line with UKHSA updated guidelines, Influenza: treatment and prophylaxis using anti-viral agents.

April 2024 — reviewed. A literature search was conducted in April 2024 to identify evidence-based guidelines, UK policy, systematic reviews, and key randomized controlled trials published since the last revision of the topic. No major changes to recommendations have been made.

January 2023 — minor update. Information that the Department of Health and Social Care (DHSC) notifies GPs directly if the national surveillance scheme indicates that influenza is circulating in the community has been added to this topic.

August 2020 — minor update. Broken URL link updated.

April 2019 — reviewed. A literature search was conducted in April 2019 to identify evidence-based guidelines, UK policy, systematic reviews, and key randomized controlled trials published since the last revision of the topic. 

October 2015 — minor update. Following an update to the Summary of Product Characteristics for Tamiflu^® (oseltamivir), the topic has been updated to reflect that oseltamivir is now licensed for:

• The treatment of influenza in adults and children (including full-term neonates) who present with symptoms typical of influenza, when influenza virus is circulating in the community.
• The post-exposure prophylaxis of influenza in:
  • Adults and children aged 1 year and over following contact with a clinically diagnosed influenza case when influenza virus is circulating in the community.
  • Infants younger than 1 year of age during a pandemic influenza outbreak.

December 2014 — minor update. Topic was checked to ensure that it is in line with the recently published Public Health England (PHE) guideline The treatment and prophylaxis of influenza, the recommendations have not changed but some minor text changes have been made.

October 2013 — reviewed. A literature search was conducted in September 2013 to identify evidence-based guidelines, UK policy, systematic reviews, and key RCTs published since the last revision of the topic. The following revisions have been made in line with recommendations from the Health Protection Agency(HPA) HPA guidance on use of antiviral agents for the treatment and prophylaxis of influenza and the UK Teratology Information Service (UKTIS) Use of oseltamivir in pregnancy:

• Oseltamivir is now recommended to be prescribed to otherwise healthy people if the prescriber feels that the person is at risk of developing serious complications from influenza.
• People considered to be 'at risk' from influenza has been revised to include women up to two weeks post partum and people with morbid obesity (body mass index of 40 or more).
• Oseltamivir is now recommended over zanamivir for the treatment of pregnant women exposed to the influenza virus, except in cases of known or suspected oseltamivir resistance.

The scope of the topic had been reduced to cover only seasonal influenza.

February 2013 — minor update. The 2013 QIPP options for local implementation have been added to this topic.

October 2012 — minor update. The 2012 QIPP options for local implementation have been added to this topic.

November 2011 — minor update. The doses of oseltamivir in renal impairment have been updated in line with the British National Formulary (BNF). Issued in December 2011.

October 2011 — minor update. The references have been revised to include updated guidance from the Department of Health's Immunisation against infectious disease — the 'Green Book' chapter 19, Influenza. 

July 2011 — minor update. More exact paracetamol dosing for children has been introduced by the Medicines and Healthcare products Regulatory Agency. Prescriptions have been updated to reflect the revised dosing. 

June 2011 — minor update. The 2010/2011 QIPP options for local implementation have been added to this topic. 

February 2011 — minor update. Recent advice from the Chief Medical Officer regarding prescribing antivirals to people who are not in clinical risk groups has been added. 

November 2010 — minor update. Part XVIIIB of the Drug tariff, which defines the circumstances in which oseltamivir and zanamivir may be prescribed, has been updated.

September 2010 — minor update. Text has been added to remind prescribers that antiviral drugs should only be prescribed when national surveillance schemes indicate that influenza is circulating in the community. 

July 2010 — minor update. Zanamivir and oseltamivir are no longer 'black triangle' drugs. Prescriptions updated. 

February 2010 — minor update. A recent Drug safety update from the Medicines and Healthcare products Regulatory Agency (MHRA) indicates that there remains no evidence to suggest that zanamivir and oseltamivir carry any risks to pregnancy. 

March to August 2009 — converted from CKS guidance to CKS topic structure. The evidence-base has been reviewed in detail, and recommendations are more clearly justified and transparently linked to the supporting evidence. The scope of the topic had been reduced to cover only seasonal influenza. Information on avian influenza will be covered in a subsequent CKS topic.

June 2009 — minor update. Additional swine flu link added. Links to information sources regarding 'swine flu' have been added to Have I got the right topic?

November 2008 — minor update. Updated to include a review of NICE technology appraisal guidance 67 previously issued in September 2003, evaluating the use of oseltamivir, amantadine, and zanamivir for the prophylaxis of influenza.

August 2008 — minor update. Updated reference added for the WHO pandemic alert phase 3: algorithm for the management of returning travellers and visitors from countries affected by avian influenza (H5N1) presenting with febrile respiratory illness: recognition, investigation and initial management. 

May 2007 — minor update. New safety information from the European Medicines Evaluation Agency (EMEA) on neuropsychiatric adverse effects with oseltamivir added. 

April to June 2006 — reviewed. Validated in September 2006 and issued in October 2006.

November 2005 — updated to include information on how to manage suspected avian influenza and also to incorporate information on two additional groups that the Chief Medical Officer (CMO) now recommends should receive flu immunization. 

July 2005 — update to prescriptions for oseltamivir. 

April 2005 — minor update. Oseltamivir and zanamivir may only be prescribed on the NHS in certain circumstances and the prescription must be endorsed 'Selected List Scheme' ('SLS'). 

September 2004 — updated to include the latest update from the CMO on the influenza immunization programme 2004/2005. 

October 2003 — updated to incorporate Guidance on the use of oseltamivir and amantadine for the prophylaxis of influenza, technology appraisal guidance no. 67, issued by the National Institute for Health and Care Excellence (NICE) (September 2003); Guidance on the use of zanamivir, oseltamivir and amantadine for the treatment of influenza, technology appraisal guidance no. 58, issued by NICE; and the influenza immunization programme 2003/2004 issued by the CMO. 

September 2002 — reviewed. Validated in December 2002 and issued in February 2003.

April 2001 — updated. Issued in October 2001.

July 1999 — written. Validated in October 1999 and issued in January 2000.

New evidence

Evidence-based guidelines

No new evidence-based guidelines since 1 April 2024.

HTAs (Health Technology Assessments)

No new HTAs since 1 April 2024.

Economic appraisals

No new economic appraisals relevant to England since 1 April 2024.

Systematic reviews and meta-analyses

• Zhao, Y., Gao, Y., Guyatt, G., et al. (2024). Antivirals for post-exposure prophylaxis of influenza: a systematic review and network meta-analysis. medRxiv, 2024-05. [Free Full-text]
• Gao Sr, Y., Guyatt, G., Uyeki, T. M., et al. (2024). Antivirals for treatment of severe influenza: a systematic review and network meta-analysis of randomized controlled trials. medRxiv, 2024-05. [Free Full-text]

Primary evidence

• Laffin, L. J., Kopjar, B., Melgaard, C., et al. (2025). Lorundrostat Efficacy and Safety in Patients with Uncontrolled Hypertension. New England Journal of Medicine. [Abstract]
• Monto, A. S., Kuhlbusch, K., Bernasconi, C., et al. (2025). Efficacy of Baloxavir Treatment in Preventing Transmission of Influenza. New England Journal of Medicine, 392(16), 1582-1593. [Abstract]

New policies

No new national policies or guidelines since 1 April 2024.

New safety alerts

No new safety alerts since 1 April 2024.

Changes in product availability

No changes in product availability since 1 April 2024.

Basis for recommendation

The information on the clinical features of influenza infection is based on the UK Health Security Agency (UKHSA) Guidance on use of antiviral agents for the treatment and prophylaxis of seasonal influenza [UKHSA, 2025], the National Institute for Health and Care Excellence (NICE) technology appraisal Amantadine, oseltamivir and zanamivir for the treatment of influenza [NICE, 2014], the British Medical Journal (BMJ) Best Practice guideline Influenza infection [BMJ Best Practice, 2024], the Infectious Diseases Society of America (IDSA) clinical practice guideline 2018 Update on Diagnosis, treatment, chemoprophylaxis, and institutional outbreak management of seasonal influenza [IDSA, 2019], and expert opinion in a narrative review Influenza [Paules, 2017].

Basis for recommendation

This information is largely based on expert opinion in a medical textbook Influenza in practice [Jennings, 2005], the UK Health Security Agency Guidance on use of antiviral agents for the treatment and prophylaxis of seasonal influenza [UKHSA, 2025] and the British Medical Journal (BMJ) Best Practice guideline Influenza infection [BMJ Best Practice, 2024].

Sepsis

• The National Institute of Health and Care Excellence (NICE) highlights that sepsis should be considered as a diagnosis at first contact with NHS services for all people with acute respiratory infection [NICE, 2023].

When should I prescribe an antiviral drug for someone with influenza?

• Note: people with complicated influenza will typically require admission to hospital. For further information, see the section on follow up and admission.
• For people with uncomplicated influenza who are being treated in primary care:
  • If COVID-19 is a possible differential diagnosis, arrange a PCR test to rule this out when considering prescribing an antiviral to treat influenza.
    • COVID-19 point-of-care testing with a lateral flow device may also be used to inform antiviral use, but is not a substitute for PCR testing.
    • If point-of-care testing is unavailable, an influenza antiviral should be started promptly without awaiting PCR results if influenza is considered to be highly probable (such following close contact with a confirmed case).
    • If available, testing for influenza should be undertaken alongside COVID-19 testing but is not required for influenza antiviral initiation.
  • Prescribe an antiviral drug (oral oseltamivir or inhaled zanamivir) for people with influenza if all of the following apply: 
    • The national surveillance scheme indicates that influenza is circulating.
    • The person is in an 'at risk' group of people who likely have a poorer prognosis from influenza than otherwise healthy people.
    • The person can start treatment within 48 hours of the onset of symptoms (36 hours in the case of zanamivir in children).
    • Starting treatment after 48 hours of the onset of symptoms (or 36 hours in the case of zanamivir in children) is an off-label use and clinical judgement should be exercised.
  • Consider prescribing oral oseltamivir for previously healthy people with influenza if all of the following apply:
    • The person is not in an 'at risk' group, but is at serious risk of developing complications.
    • The national surveillance scheme indicates that influenza is circulating.
    • The person is able to start treatment within 48 hours of the onset of symptoms. 
• Seek advice about the use of antivirals from a local medicine specialist if required.

Which antiviral drug should I prescribe if treatment is indicated?

• For uncomplicated influenza in people: 
  • Who were previously healthy — no antiviral treatment is normally indicated, unless the person is at serious risk of developing serious complications from influenza, then prescribe oral oseltamivir.
  • Who are in an at risk group (including women who are pregnant), but are not severely immunosuppressed — prescribe oral oseltamivir. Do not wait for laboratory confirmation. 
  • Who are severely immunosuppressed, and the dominant strain has:  
    • A lower risk of oseltamivir resistance (for example, A [H3N2] influenza B) — prescribe oral oseltamivir.
    • A higher risk of oseltamivir resistance (for example, A [H1N1]) — prescribe inhaled zanamivir, or if this is unsuitable or inappropriate, prescribe oral oseltamivir and follow up.
• See the prescribing information sections on Oseltamivir and Zanamivir for recommended doses, contraindications, cautions, and possible adverse effects of these drugs.
• Seek advice about the use of antivirals from a local medicine specialist if required.

What advice should I give someone to help manage influenza?

• Advise the person:
  • To drink adequate fluids to avoid dehydration. 
  • To take paracetamol or ibuprofen for symptomatic relief. 
  • To rest in bed if they feel fatigued.
  • To stay off work or school if they feel unable to attend — for most people, about 1 week will be adequate.
  • That fever and associated systemic symptoms of uncomplicated influenza usually resolve after about 1 week, although some symptoms (such as cough and fatigue) may persist for up to 2 weeks after resolution of fever.
  • About the symptoms of complicated influenza and to seek medical advice should their condition deteriorate. 
• Advise the person that routine follow up is not necessary, but they should:
  • Seek urgent medical attention if they develop shortness of breath or pleuritic chest pain, or if they start to cough up blood (haemoptysis) — this may indicate the development of pneumonia secondary to bacterial superinfection. 
  • Arrange a follow-up appointment if there is no improvement after 1 week (that is, they are still significantly ill), or they are deteriorating.
  • Have a lower threshold for seeking help if the person with influenza is a baby or young child.

When should I follow up or admit a person with influenza?

• Consider follow up particularly in people at high risk of serious complications (for example, people aged over 65 years) within 1 week, to confirm that symptoms are improving and to rule out secondary complications.
• Consider admission to hospital, depending on clinical judgement, if:
  • A complication of influenza occurs.
    • Pneumonia is a common complication that may be indicated by lower respiratory tract distress (characterized by laboured breathing, shortness of breath, pleuritic chest pain, and haemoptysis). It may occur immediately, or up to 2 weeks, after initial symptoms of influenza. For more information, see the CKS topics on Chest infections - adult and Cough - acute with chest signs in children.
  • The person has a co-existing medical condition that puts them at high risk of complications — for example, people with diabetes mellitus (particularly type 1) are at risk of hyperglycaemia, ketoacidosis, and diabetic coma.
  • An alternative diagnosis is suspected.
• Also consider admission to hospital in children:
  • Aged under 2 years if they are in an 'at risk' group.
  • If they have febrile symptoms that may indicate serious illness. For more information see the CKS topic on Feverish children - risk assessment and management.

When should I prescribe antiviral drugs for post-exposure prophylaxis?

• Prescribe an antiviral drug for post-exposure prophylaxis (PEP) if all the following circumstances apply:
  • The person has had contact with a person strongly suspected (on the basis of community prevalence and clinical features) or known to have influenza.
  • The person is in an ‘at risk’ group and has not been adequately protected by vaccination because:
    • They have not been vaccinated within the same influenza season.
    • There has been less than 14 days between vaccination and date of contact with influenza.
    • There is low confidence the vaccine gives good protection against the influenza strain they are known or suspected to have been infected with based on testing of the case or national surveillance of circulating strains (for example, where national surveillance indicates that a drifted strain is circulating).
    • Note: if the person has been exposed due to a localised outbreak (for example, in a care home) PEP can be considered regardless of vaccination status.
  • The person can start PEP within 48 hours of this contact for oseltamivir or 36 hours for zanamivir.
    • PEP after 48 hours for oseltamivir or 36 hours for zanamivir is off-label use but can be done in consultation with a local infection specialist, such as a virologist, or a consultant in health protection. Note that in institutional outbreaks, ongoing exposures may occur due to new-onset cases and may support initiation beyond 48 or 36 hours from exposure to the index or primary cases.

How should I manage a person requiring post-exposure prophylaxis?

• If post-exposure prophylaxis is indicated, prescribe oral oseltamivir or inhaled zanamivir (as appropriate). 
  • For people at risk of complicated influenza (including pregnant women, but excluding severely immunosuppressed people and children aged under 5 years), prescribe:
    • Oral oseltamivir once daily for 10 days if the identified strain in the index case or dominant circulating strain is lower risk for oseltamivir resistance (for example, influenza A [H3N2], influenza B), or is known to be higher risk for oseltamivir resistance (for example, influenza A [H1N1]).
    • Inhaled zanamivir daily for 10 days if the person has been exposed to suspected or confirmed oseltamivir-resistant influenza.
  • For severely immunosuppressed adults and children aged 5 years and over, prescribe:
    • Oral oseltamivir once daily for 10 days if the identified strain in the index case or dominant circulating strain is lower risk for oseltamivir resistance (for example influenza A [H3N2] and influenza B). 
    • Inhaled zanamivir daily for 10 days if the identified strain in the index case or dominant circulating strain is higher risk for oseltamivir resistance (for example, influenza A [H1N1]), or if this is unsuitable or inappropriate, prescribe oral oseltamivir once daily for 10 days.
    • Inhaled zanamivir daily for 10 days if the person has been exposed to suspected or confirmed oseltamivir-resistant influenza. If this is unsuitable or inappropriate seek specialist advice.
  • For children aged under 5 years in at risk groups, including severely immunocompromised children:
    • Prescribe oral oseltamivir once daily for 10 days if the identified strain in the index case or dominant circulating strain is lower risk for oseltamivir resistance (for example, influenza A [H3N2], influenza B), or is known to be higher risk for oseltamivir resistance (for example, influenza A [H1N1]).
    • If the child has been exposed to suspected or confirmed oseltamivir-resistant influenza, seek specialist advice.
  • Note: when administering post-exposure prophylaxis to people who are immunosuppressed who are contacts of a confirmed case, ensure diagnostic sampling for influenza detection prior to use of the antiviral. 
    • If testing shows that the person is infected with influenza, commence a full course of treatment dose antivirals.
  • See the Prescribing information sections on oseltamivir and zanamivir for recommended doses, contraindications, cautions, and possible adverse effects of these drugs.
• Arrange for the person to receive influenza immunization if this has not already been done in the present influenza season.
  • Note: the efficacy of the vaccine may be reduced if it is administered within 2 weeks of use of an influenza antiviral agent.
• Inform the person that although antiviral drugs help prevent influenza, they are not completely effective. Provide advice about symptomatic treatment and when to seek medical attention if influenza develops. 

Dose

Table 1. Recommended doses of oseltamivir.

Contraindications and cautions

• Prescribe oseltamivir with caution to people with renal impairment — dose adjustments may be necessary.

[EMC, 2021; BNF, 2024]

Adverse effects

• Common adverse effects include:
  • Abdominal pain.
  • Conjunctivitis.
  • Dizziness and vertigo.
  • Earache.
  • Headache.
  • Nausea and vomiting.
  • Otitis media.
• Uncommon adverse effects include:
  • Arrhythmia.
  • Consciousness impaired.
  • Skin reactions.
• Rare adverse effects include: 
  • Abnormal behaviour abnormal. 
  • Angioedema. 
  • Anxiety, confusion, delirium, delusions, hallucination, and self-injurious behaviour.
  • Haemorrhage. 
  • Hepatic disorders. 

[EMC, 2021; BNF, 2024]

Pregnancy and breastfeeding

• Pregnancy
  • There is no evidence of harm following use of oseltamivir during pregnancy.
  • Oseltamivir can be used in women who are pregnant when the potential benefit outweighs the risk.
    • Oseltamivir remains the first line option for the vast majority of pregnant women with influenza, including during seasons that are dominated by influenza A(H1N1).
• Breastfeeding
  • Oseltamivir and its active metabolite are excreted in breast milk. 
  • Safety data are limited, however, oseltamivir can be used in women who are breastfeeding when the potential benefit outweighs the risk (for example, during a pandemic).
  • Oseltamivir is the preferred drug in women who are breastfeeding.

[EMC, 2021; UKHSA, 2025; UKTIS, 2023b; BNF, 2024]

Drug interactions

• Leflunomide/teriflunomide — levels of the active metabolite of oseltamivir may be increased. Monitor for adverse effects and adjust oseltamivir dose if required. 
• Tolvaptan — levels of the active metabolite of oseltamivir may be increased. Monitor for adverse effects and adjust oseltamivir dose if required. 
• Warfarin — isolated case of raised INRs has been reported.  

[BNF, 2024; Preston, 2024]

Dose

• The dose of inhaled zanamivir for adults and children aged over 5 years for: 
  • Treatment of influenza is 10 mg twice daily for 5 days.
  • Post exposure prophylaxis of influenza is 10 mg once daily for 10 days.
• Zanamivir is not licensed for use in children aged under 5 years.

[UKHSA, 2025; EMC, 2023; BNF, 2024]

Contraindications and cautions

• Do not prescribe zanamivir to people with milk protein allergy. 
• Prescribe zanamivir with caution to people with:
  • Asthma or chronic pulmonary disease — risk of bronchospasm. If close monitoring is not possible, avoid use.
  • Uncontrolled chronic illness.

[EMC, 2023; BNF, 2024]

Adverse effects

• Common adverse effects include:
  • Skin reactions.
• Uncommon adverse effects include:
  • Bronchospasm, dyspnoea, and throat tightness.
  • Dehydration.
  • Oropharyngeal oedema.
  • Presyncope. 
  • Severe cutaneous adverse reactions (SCARs).
  • Urticaria.
• Other adverse effects include: 
  • Abnormal b​​​​​​ehaviour, and psychiatric disorder.
  • Delirium, hallucination, and level of consciousness decreased. 
  • Seizure.

[EMC, 2023; BNF, 2024]

Pregnancy and breastfeeding

• Pregnancy
  • Safety data are limited, but do not suggest harm following use of zanamivir in pregnancy. Exposure via the inhaled route is likely to result in only low levels of fetal exposure.
  • Zanamivir can be used in women who are pregnant when the potential benefit outweighs the risk (for example, during a pandemic).
    • Oseltamivir is the first line option for the vast majority of pregnant women with influenza, including during seasons that are dominated by influenza A(H1N1).
• Breastfeeding
  • Safety data is limited, however, the amount of zanamivir excreted in breast milk is probably too small to be harmful.
  • Zanamivir can be used in women who are breastfeeding when the potential benefit outweighs the risk (for example, during a pandemic).
  • However, the manufacturer advises that as a risk to the breastfed child cannot be excluded a decision must be made whether to discontinue breastfeeding or to discontinue/abstain from treatment, taking into account the benefit of breastfeeding for the child and the benefit of therapy for the woman.

[UKHSA, 2025; UKTIS, 2022; EMC, 2023; BNF, 2024]

Drug interactions

• There are no significant drug interactions for zanamivir.

[Preston, 2024]

The doses of baloxavir marboxil for the treatment of and post-exposure prophylaxis for influenza in adults are as follows: 

• Body weight less than 20 kg — a single dose of 2 mg /kg.
• Body weight between 20 kg – 79 kg — a single dose of 40 mg.
• Body weight 80 kg and over — a single dose of 80 mg.

The doses of baloxavir marboxil for the treatment of and post-exposure prophylaxis for influenza in children are as follows: 

• Aged 12 to 17 years with body weight up to 79 kg — a single dose of 40 mg.
• Aged 12 to 17 years with body weight over 80 kg — a single dose of 80 mg.

[BNF, 2025; UKHSA, 2025]

• Baloxavir marboxil is contraindicated in people with hypersensitivity to the active substance or to any of the excipients.

[EMC, 2025]

Adverse effects of baloxavir marboxil include:

• Immunological
  • Anaphylaxis (frequency not known)
  • Anaphylactic reactions (frequency not known)
  • Hypersensitivity (frequency not known)
• skin disorders
  • Urticaria (uncommon)
  • Angioedema (frequency not known)

[EMC, 2025]

Pregnancy

• Baloxavir marboxil is not currently recommended for use in pregnant individuals due to insufficient safety and efficacy data for treating pregnant and postpartum patients.

Breast feeding

• Seek specialist advice. Baloxavir is licensed from 3 weeks of age and if there is lactational transfer this may not be disadvantageous to infants exposed to maternal influenza, though is unlikely to be protective

[UKHSA, 2025]

• Products that contain polyvalent cations may decrease plasma concentrations of baloxavir. Xofluza should not be taken with products that contain polyvalent cations such as laxatives, antacids or oral supplements containing iron, zinc, selenium, calcium or magnesium.
• Baloxavir marboxil might decrease the efficacy of Influenza vaccine (live). Manufacturer advises separating administration.

[BNF, 2025; EMC, 2025]