Treatment

• Rest, fluids, and fever control: Paracetamol (acetaminophen) can help fever and body aches. Avoid aspirin in children or teenagers because of Reye syndrome risk.
• Antiviral treatment: Oseltamivir is the usual first-line antiviral. It works best if started within 48 hours of symptom onset, but should still be started as soon as possible in people with severe illness, hospitalization, pregnancy, or higher risk of complications.
  • For a typical adult with normal kidney function, the commonly used regimen is 75 mg orally twice daily for 5 days, prescribed by a clinician.
  • Dose adjustment is needed in kidney impairment. Pediatric doses depend on age and weight.
• Alternatives in selected patients include inhaled zanamivir, intravenous peramivir, or single-dose baloxavir. Zanamivir should generally be avoided in people with asthma or COPD because it can cause bronchospasm.
• Antibiotics do not treat swine flu. They are used only if a clinician suspects a bacterial complication, such as pneumonia.

Who should receive antivirals urgently

• Pregnant or recently postpartum
• Under 5 years old, especially under 2
• Over 65
• Has asthma, COPD, heart disease, diabetes, kidney/liver disease, neurologic disease, or immunosuppression
• Very unwell, has worsening symptoms, or needs hospital care

Emergency warning signs

1. Antiviral treatment

• Hospitalized patients
• Severe, worsening, or complicated illness
• Pregnancy or up to 2 weeks after delivery
• Age under 5 years, especially under 2 years
• Age 65 years or older
• Asthma, COPD, heart disease, diabetes, kidney disease, neurologic disease, or weakened immunity
• Marked obesity

2. Supportive care

• Rest and drink adequate fluids.
• Use paracetamol/acetaminophen for fever and body aches.
• Ibuprofen can be used by many adults if they have no kidney disease, stomach ulcer/bleeding risk, or other contraindication.
• Avoid aspirin in children and teenagers with a viral illness because of the risk of Reye syndrome.
• Stay home, limit close contact, wear a mask around others, cover coughs/sneezes, and wash hands.

3. Antibiotics are not routine

Seek urgent medical care now if there is

• Trouble breathing, rapid breathing, blue/grey lips, chest pain
• Confusion, fainting, severe weakness, seizures
• Inability to keep fluids down, dehydration, very little urine
• Fever or cough that improves then returns or worsens
• In a child: fast breathing, poor feeding, unusual sleepiness, or signs of dehydration

Latest influenza antiviral-treatment guidance

• CDC, 2025-2026 seasonal influenza clinical recommendations for US practice
• WHO clinical practice guideline, published September 2024 and summarized in BMJ in 2026, with a more restrictive, evidence-based approach for non-severe influenza

Where both approaches agree

1. Do not delay treatment for test results when influenza is suspected in a patient who is hospitalized, severely ill, clinically deteriorating, or at high risk of complications.
2. Start antiviral treatment as early as possible. Benefit is greatest within 48 hours, but treatment is still advised for severe or hospitalized illness even when presentation is later.
3. Oseltamivir remains the standard practical treatment for severe or hospitalized influenza.
4. Antibiotics do not treat influenza itself. Use them only if bacterial co-infection is suspected or confirmed.

CDC approach: current US clinical practice

• Hospitalized patients
• Outpatients with severe, complicated, or progressive disease
• Outpatients at higher risk of complications, such as pregnancy, age under 5 or 65 and over, chronic heart/lung/metabolic/neurologic/kidney disease, or immunocompromise

• Hospitalized or severe/progressive influenza: oral or enteric oseltamivir as soon as possible. Do not substitute baloxavir routinely in hospitalized disease because evidence is limited.
• Uncomplicated outpatient influenza within 48 hours: oseltamivir, baloxavir, zanamivir, or peramivir may be selected by the prescriber.
• Pregnancy: oseltamivir is preferred. Baloxavir is not recommended because pregnancy data are lacking.
• Asthma/COPD or other airway disease: avoid inhaled zanamivir because of bronchospasm risk.
• Renal impairment: oseltamivir and peramivir require dose adjustment.

WHO approach: 2024 guideline

Evidence behind the recent WHO position

• Baloxavir probably shortened symptoms by about 1 day and may reduce hospital admission in high-risk patients.
• Oseltamivir shortened symptoms by about 0.75 day, an effect the authors judged not clinically important on average, and probably caused more treatment-related adverse events, mainly nausea/vomiting.
• These results should not be interpreted as a reason to withhold oseltamivir from hospitalized or seriously ill patients, where the clinical evidence base and guideline rationale differ. See Gao et al., 2025.

Bottom line

• For a patient with swine flu/H1N1 who is severely ill, hospitalized, pregnant, or high-risk, seek medical assessment promptly and start oseltamivir early if clinically indicated, without waiting for a test result.
• For an otherwise healthy person with mild flu, the benefit of antiviral therapy is limited and depends on starting very early. CDC allows treatment based on clinical judgment; WHO generally recommends against routine oseltamivir in this lower-risk group.
• The choice and dose must be individualized for age, pregnancy, kidney function, duration of symptoms, and severity.