What is the recommended treatment for influenza A vs B?

Treatment Recommendations for Influenza A vs B

Neuraminidase inhibitors (oseltamivir or zanamivir) are recommended as first-line treatment for both influenza A and B, with treatment initiated as early as possible, ideally within 48 hours of symptom onset. 1, 2

General Treatment Principles

• Antiviral treatment is recommended as soon as possible for all persons with suspected or confirmed influenza who:

  • Are hospitalized 1
  • Have severe, complicated, or progressive illness 1
  • Are at higher risk for influenza complications 1

• Early initiation of treatment (within 48 hours of symptom onset) provides the greatest benefit, but treatment should not be withheld if beyond this window, especially in severely ill patients 1

• Treatment should not be delayed while waiting for confirmatory test results in high-risk patients or those with severe illness 2, 3

Medication Options for Both Influenza A and B

Oseltamivir (Oral)

• First-line treatment option for both influenza A and B 1, 4
• Indicated for treatment of acute, uncomplicated influenza A and B in patients 2 weeks of age and older 4
• Standard adult dose: 75 mg twice daily for 5 days 3
• Pediatric dosing is weight-based:
  • ≤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

  • 9-11 months: 3.5 mg/kg twice daily
  • 0-8 months: 3 mg/kg twice daily 2
• Most common side effect is vomiting (in approximately 5% of patients) 2

Zanamivir (Inhaled)

• Alternative option for both influenza A and B 1, 5
• Indicated for treatment of uncomplicated influenza A and B in adults and children ≥7 years 5
• Not recommended for patients with underlying airways disease due to risk of bronchospasm 5
• May be preferred for confirmed influenza B outbreaks based on some evidence of better efficacy against influenza B compared to oseltamivir 6

Important Differences Between Influenza A and B Treatment

• More clinical data are available concerning the efficacy of neuraminidase inhibitors for treatment of influenza A than for influenza B 1

• Observational studies suggest oseltamivir might be less effective for influenza B than influenza A:

  • Japanese children with influenza A resolved fever and stopped shedding virus more quickly than children with influenza B when treated with oseltamivir 1
  • Zanamivir appears to have more equal effectiveness against both influenza A and B strains 6

• When influenza B is confirmed or strongly suspected to be circulating in the community, zanamivir may be the preferred treatment option, especially in patients who can use the inhaler properly and don't have underlying respiratory disease 6

Special Populations and Considerations

• For severely ill patients or immunocompromised patients, treatment is recommended regardless of time since symptom onset 1, 3

• For hospitalized patients, oseltamivir treatment initiated within 2 days of symptom onset is associated with earlier hospital discharge 1

• For high-risk patients (elderly, immunocompromised, pregnant women, young children), treatment should be initiated regardless of duration of symptoms 2, 3

• Treatment may reduce the risk of complications such as pneumonia, respiratory failure, and death when initiated early 1

Clinical Pearls and Pitfalls

• Do not delay treatment while awaiting confirmatory test results in high-risk patients or those with severe illness 2

• Antiviral medications are not a substitute for vaccination, which remains the cornerstone for influenza prevention 1, 6

• The benefit of treatment is greatest when initiated within 24 hours of symptom onset 7

• Consider empiric treatment during influenza season for patients presenting with typical symptoms (fever, cough, myalgia), especially during community outbreaks 1

• When treating influenza B specifically, consider zanamivir if the patient has no contraindications to inhaled therapy, as it may have better efficacy against influenza B than oseltamivir 6