Recommended Antiviral Therapy for Influenza A and B
Start treatment immediately with a single neuraminidase inhibitor (NAI)—either oral oseltamivir, inhaled zanamivir, or intravenous peramivir—for patients who are hospitalized, have severe/progressive illness, are at high risk for complications, are under 2 years or over 65 years old, or are pregnant/postpartum. 1
First-Line Treatment Options
The IDSA 2019 guidelines provide clear direction on antiviral selection 1:
- Oral oseltamivir (most widely used and studied)
- Inhaled zanamivir (particularly effective against influenza B and oseltamivir-resistant influenza A)
- Intravenous peramivir (single-dose option)
Do not combine NAIs or use higher than FDA-approved doses for seasonal influenza. 1
Treatment Duration
- Uncomplicated influenza in healthy outpatients: 5 days of oseltamivir or zanamivir, OR single dose of IV peramivir 1
- Immunocompromised patients or severe lower respiratory disease (pneumonia/ARDS): Consider longer duration due to protracted viral replication 1
Who Must Receive Treatment
Start antivirals as soon as possible (ideally within 48 hours of symptom onset) for 1:
- Any hospitalized patient, regardless of illness duration
- Outpatients with severe or progressive illness
- High-risk patients: chronic medical conditions, immunocompromised
- Children <2 years and adults ≥65 years
- Pregnant women and up to 2 weeks postpartum
For otherwise healthy outpatients not at high risk, treatment is optional but can be considered 1.
Newer Evidence on Baloxavir
Recent WHO guidelines (2024) conditionally recommend baloxavir for non-severe influenza in patients at high risk of progression to severe illness 2, 3. Baloxavir shows superior viral load reduction compared to oseltamivir, though resistance variants can emerge 4. However, baloxavir access remains limited in many settings, particularly low- and middle-income countries 5.
Critical Pitfalls to Avoid
Bacterial coinfection management 1:
- Empirically treat bacterial coinfection in patients presenting with severe disease (extensive pneumonia, respiratory failure, hypotension)
- Investigate bacterial coinfection if patients deteriorate after initial improvement
- Consider bacterial workup if no improvement after 3-5 days of antivirals
Do NOT use 1:
- Combination NAI therapy
- Routine higher doses of NAIs
- Antivirals alone if bacterial coinfection is suspected in severe disease
Resistance Testing Considerations
Consider NAI resistance testing for 1:
- Patients developing influenza while on/after NAI prophylaxis
- Immunocompromised patients with persistent viral replication (>7-10 days) who remain ill during treatment
- Patients receiving subtherapeutic NAI dosing
- Severe influenza patients not improving with NAI treatment
Special Considerations for Zanamivir
Zanamivir is more effective against influenza B and works against most oseltamivir-resistant influenza A strains, but the inhaled formulation is less suitable for patients with severe illness or underlying airway disease 4. IV zanamivir is approved in some countries for hospitalized patients 4.