Paediatric Influenza

Introduction

This policy provides guidance on the treatment of presumed/confirmed influenza infection and prophylaxis following significant contact with influenza. The update aligns with the updated UK Health Security Agency (UKHSA) Guidance on Use of Antiviral Agents for the Treatment and Prophylaxis of Seasonal Influenza (updated 4 November 2025). 

Scope and Purpose

All children at risk of severe influenza, infected with influenza or those in contact with influenza.
 
Identification of children at risk of severe influenza infection and appropriate immunisation. Appropriate treatment of cases of presumed/confirmed influenza and appropriate management of cases of significant contact with confirmed influenza.

Definitions

Non-severe influenza
Influenza presenting with fever, coryza, generalised symptoms (headache, malaise, myalgia, arthralgia) and sometimes gastrointestinal symptoms, but without any features of complicated influenza.
 
Severe 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
Principles

​Treatment

Children with risk factors (See table 1) should be treated with antivirals if admitted to hospital with confirmed influenza infection. During periods of high local influenza prevalence, empirical treatment with antivirals should be considered in children with severe respiratory distress requiring critical care whilst awaiting results. If influenza PCR results are subsequently negative in cases of empirically treated infection, antivirals can be stopped. In general, influenza is less severe in children than in adults.

Only treat children without risk factors with confirmed or presumed influenza infection if they require admission to PHDU / PICU. Where indicated, treatment should be initiated as soon as possible (ideally within the first 48 hours of symptoms).

The 2025 UKHSA guideline states that the 1st antiviral choice is oseltamivir (PO or NG), irrespective of immune function and circulating subtype. Treatment of severely immunosuppressed patients with severe influenza with zanamivir is only recommended in circumstances where oseltamivir is unable to be administered or is unlikely to be effective. There is a greater body of evidence to support use of oseltamivir in severe influenza.

NOTE: children can be positive by PCR for influenza A or B (or both) following immunisation with the nasal live attenuated influenza vaccine. Detection is most common within the first week following administration of the intranasal vaccine, although live vaccine virus can be detected by PCR for up to 3 weeks after vaccination – having access to the cycling threshold (ct) value may help avoid an incorrect diagnosis in such cases.

​Prophylaxis

Only children with risk factors (See Table 1) should receive prophylaxis following close contact with someone with confirmed influenza including exposure to confirmed household contact. If indicated, prophylaxis should only be used if started within 48 hours of the last contact (use after 48 hours with specialist advice only).

Table 1. Risk factors for severe influenza infection

1
Under 6 months old from expected delivery date
2
Asthma on regular inhaled steroids
3
Cystic fibrosis, Primary ciliary dyskinesia or bronchiectasis
4
Chronic lung disease on home oxygen or long-term ventilation
5
Congenital Heart Disease apart from minor ASD / VSD / PS
6
Significant Immune deficiency (any cause including HIV and long-term oral steroids)
7
Neuromuscular disease e.g. SMA, Duchenne etc
8
Significant neurodevelopmental delay
9
Other chronic disease where clinician feels decompensation may result from influenza
Risk Factors
Mortality rate per 100,00 population
Immunosuppression
20.0
Chronic liver disease
15.8
Chronic neurological disease
14.7
Chronic renal disease
4.8
In a risk group (average)
4.0
Chronic heart disease
3.7
Chronic respiratory disease
2.4
Diabetes
2.2
Not in an risk group
0.4
Treatment
The 2 classes of direct acting antivirals (DAA) licenced in the UK for the treatment of seasonal influenza include neuraminidase inhibitors (NAI) (oral (PO) oseltamivir and inhaled (INH) or intravenous (IV) zanamivir) which target the NA glycoprotein; and cap-dependent endonuclease inhibitors (CENi) (PO baloxavir marboxil) which act on the polymerase acidic (PA) protein. Baloxavir marboxil has been studied in treatment trials involving patients older than 5 years, with adverse events similar to those observed in adults. There are limited data available for patients aged 5 years or younger. The pharmacokinetics of baloxavir marboxil in paediatric patients under 1 year of age have not been established

Indications

  • For non-severe influenza in a child with risk factors (See above), oseltamivir is first-line.
  • For severe influenza, first-line remains oseltamivir PO (or NG); alternatives include inhaled zanamivir, and if oral or inhaled therapy not tolerated, intravenous (IV) zanamivir or single dose oral baloxavir after specialist consultation with paediatric ID team (Southampton)if use considered in a child. NOTE: baloxavir it is non-formulary in Hampshire and Isle of Wight and not stocked at UHS; it may be ordered on an individual named patient basis but this may result in a delay obtaining the drug).
  • The consensus reached by the Wessex network is that children without risk factors (including immunosuppression) with confirmed or suspected influenza should only be treated with oseltamivir if severe enough to require admission to PHDU or PICU.

Duration and Special Considerations

  • Standard treatment course for oseltamivir: 5 days.
  • Consider extending to 10 days in immunosuppressed children or severe/critically ill cases, after discussion with infectious diseases / pharmacy specialists.
  • Monitor for poor response; in cases of suspected resistance or non-response, specialist input is strongly advised
Oseltamivir should be used as standard treatment, even for infection in the immunocompromised child. Starting antivirals early, within 48 hours of illness onset, shows the greatest benefit. Treatment beyond 48 hours is off label but may also be valuable, even if started up to 5 days after symptom onset.  In settings where clinical trials for oseltamivir are ongoing (e.g., REMAP-CAP) it may be appropriate to withold the commencement of antiviral treatment (including in PICU) pending the opportunity to recruit children into the study.
​
For children within confirmed H1N1 not responding to oseltamivir, a follow up respiratory specimen should be collected 5 days after commencing treatment to check that the virus remains sensitive to the drug. 

Table 1. Oseltamivir PO (TREATMENT DOSE, 5-day course​)

Age Group
Dose
Premature (< 36 weeks post-conception)
1 mg/kg twice daily (off-label) 
Infants under 12 months (≥ 36 weeks post-conception))
3 mg/kg twice daily 
Children 1–12 years
10–15 kg: 30 mg twice daily
>15–23 kg: 45 mg twice daily
>23–40 kg: 60 mg twice daily
​>40 kg: 75 mg twice daily 
Adults (13 years +)
< 40 kg: 60 mg twice daily
≥ 40 kg: 75 mg twice daily

Licensing & Formulations / Special-Use Notes

  • Oseltamivir oral suspension (Tamiflu®, 6 mg/mL) is available for children unable to swallow capsules.
  • Oseltamivir capsules can be opened and dispersed in water/juice before giving orally or down an enteral tube for doses ≥30mg if the liquid is not available
  • The suspension is licensed for treatment including full-term neonates; for prophylaxis in infants under 1 year, its use is off-label, and specialist advice should be sought.
  • Inhaled zanamivir is not licensed in children under 5 years.
Prophylaxis

Indications

  • Offer post-exposure prophylaxis (PEP) only when UKHSA criteria are met: significant exposure plus the contact being in a high risk-group and not fully vaccinated in the current season.
  • Use oseltamivir as first-line PEP, unless contraindicated.
  • Zanamivir inhaled may be considered for PEP in children ≥ 5 years, but is not licensed for PEP in <5 yrs.
  • Baloxavir marboxil (single dose) may be used in PEP in selected circumstances (e.g., suspected oseltamivir resistance and zanamivir not suitable), but not first-line. Use in infants < 3 weeks is contraindicated, and use requires specialist advice.
  • Start prophylaxis as soon as possible, ideally within 48 hours of last exposure. For zanamivir, start within 36 hours if possible. PEP after these windows may be off-label and should involve specialist advice.

Table 2a. Oseltamivir PO (PROPHYLAXIS, 10-day course​)

Age Group
Dose
Premature (< 36 weeks post-conception)
Seek infection specialist advice
Infants under 12 months (≥ 36 weeks post-conception))
3 mg/kg once daily 
Children 1–12 years
≤ 15 kg: 30 mg once daily
>15–23 kg: 45 mg once daily
>23–40 kg: 60 mg once daily
>40 kg: 75 mg once daily 
Adults (13 years +)
< 40 kg: 60 mg once daily
≥ 40 kg: 75 mg once daily

Table 2b. Zanamivir Inhaled (PROPHYLAXIS, 10-day course​)

Age
Dose
Children < 5 years
Not licensed for prophylaxis
Children ≥ 5 years
10 mg once daily (inhaled)

Renal and Other Considerations for Prophylaxis

  • For renal impairment in older children/adolescents (≥ 13 years), UKHSA provides a renal adjustment table (Table 8).
  • In young children (<13 yrs) with renal dysfunction, consult BNFc / pharmacy or infectious disease specialist for appropriate dosing.
  • In severely immunosuppressed children, if exposed to oseltamivir-sensitive influenza, use oral oseltamivir PEP with close follow-up.
  • If exposure is to confirmed oseltamivir-resistant virus, specialist advice is mandatory, and alternative PEP options may be required (e.g., zanamivir, baloxavir).

Severe Immunodeficiency ​includes:

  • severe primary immunodeficiency (esp T cell immunodeficiency)
  • current or recent (within six months) chemotherapy or radiotherapy for malignancy
  • solid organ transplant recipients on immunosuppressive therapy
  • bone marrow transplant recipients currently receiving immunosuppressive treatment, or who received it within the last 12 months
  • 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 ≥ 2mg/kg/day for ≥1 week in a child), and for at least three months after treatment has stopped
  • HIV infected patients with severe immunosuppression (CD4<200/μl or <15% of total lymphocytes in an adult or child over five; CD4< 500/μl or <15% of total lymphocytes in a child aged one to five; expert clinical opinion in a child aged under one)
NOTE: most children with severe immunodeficiency are still eligible to receive the live attenuated vaccine apart from those with extreme T cell immunodeficiency (SCID), oncology patients receiving chemotherapy or within 6 months of finishing or bone marrow transplant patients (up to 6 months post-BMT). NOTE: some inactivated influenza vaccines contain egg, for egg allergic children requiring the inactivated vaccine, check weblink for information.
Process for Monitoring Compliance
The purpose of monitoring is to provide assurance that the agreed approach is being followed.  This ensures that we get things right for patients, use resources well and protect our reputation.  Our monitoring will therefore be proportionate, achievable and deal with specifics that can be assessed or measured.
References
Document Version: 
2.0

Lead Authors: 
Sanjay Patel, Infectious Disease Consultant, UHS
Approving Network:
Wessex Infectious Disease Network

Date of Approval: 
November 2025

Review Due:
November 2028