What is the recommended treatment for influenza B?

Treatment of Influenza B

Oseltamivir is the preferred treatment for influenza B infection, administered at appropriate weight-based dosing for 5 days when started within 48 hours of symptom onset. 1, 2

First-Line Antiviral Options

Oseltamivir (Preferred)

• Dosing for adults: 75 mg orally twice daily for 5 days 1
• Dosing for children (≥12 months): Weight-based dosing 1
  • ≤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

• Infants 9-11 months: 3.5 mg/kg per dose twice daily
• Term infants 0-8 months: 3 mg/kg per dose twice daily
• Preterm infants: Adjusted dosing based on postmenstrual age 1

Zanamivir (Alternative)

• Adults and children ≥7 years: 10 mg (two 5-mg inhalations) twice daily for 5 days 1, 3
• Not recommended for patients with underlying respiratory disease due to risk of bronchospasm 3

Treatment Timing and Efficacy

• Treatment should be initiated as soon as possible after symptom onset, ideally within 48 hours 2
• Earlier treatment provides greater benefits:
  • Starting within 12 hours reduces illness duration by 74.6 hours (3.1 days) compared to starting at 48 hours 4
  • Starting within 24 hours reduces illness duration by 53.9 hours compared to starting at 48 hours 5
• A 2023 study showed oseltamivir reduced in-hospital mortality by 82% in patients with PCR-confirmed influenza B 6

Indications for Treatment

Treatment is particularly important for high-risk individuals 1:

• Children <2 years
• Adults ≥65 years
• Individuals with chronic medical conditions (pulmonary, cardiovascular, renal, hepatic, hematologic, metabolic, or neurologic disorders)
• Immunocompromised individuals
• Pregnant or postpartum women (within 2 weeks after delivery)
• Individuals with morbid obesity (BMI ≥40)
• Residents of nursing homes or chronic care facilities

Special Considerations

Renal Impairment

• Dose adjustment required for patients with moderate to severe renal impairment 2
• Not recommended for patients with end-stage renal disease not undergoing dialysis 2

Administration Tips

• Oseltamivir can be taken with or without food, but tolerability may be enhanced when taken with food 2, 4
• Common side effects include nausea and vomiting, which are typically transient and mild 7, 4

Common Pitfalls to Avoid

1. Delayed treatment: Efficacy decreases significantly when treatment is started >48 hours after symptom onset, though some benefit may still exist in severely ill patients 8

2. Inappropriate use in respiratory disease: Zanamivir should be avoided in patients with underlying airways disease due to risk of bronchospasm 3

3. Relying solely on antivirals: Antiviral medications are an important adjunct but not a substitute for influenza vaccination 1, 2

4. Inadequate testing: When influenza is circulating, hospitalized patients with influenza symptoms should be tested with a molecular assay with high sensitivity and specificity 1

5. Extended treatment duration: Standard treatment duration is 5 days; limited data support extending beyond this period except in critically ill patients 8

The American Academy of Pediatrics considers oseltamivir to be the preferred treatment for influenza A and B 1, and its efficacy has been demonstrated across multiple studies with significant reductions in illness duration, symptom severity, and complications when started promptly 7, 6, 4.