Current Chemoprophylaxis Recommendations for Influenza
Oseltamivir is the recommended antiviral agent for influenza chemoprophylaxis, administered at 75 mg once daily for adults and weight-based dosing for children, with baloxavir as an alternative single-dose option for patients ≥12 years. 1
Primary Indications for Chemoprophylaxis
Chemoprophylaxis should be initiated in the following specific situations:
- High-risk patients with vaccine contraindications who cannot receive influenza vaccination 1
- High-risk patients during the 2-week period after vaccination while waiting for antibody response to develop 1
- Unvaccinated family members or healthcare providers with ongoing close exposure to unimmunized high-risk children or infants <24 months 1
- Institutional outbreak control for unvaccinated staff and residents in closed settings with high-risk populations 1
- Immunocompromised patients as a supplement to vaccination, since they may not respond adequately to vaccine 1
- Post-exposure prophylaxis for family members and close contacts of confirmed influenza cases 1
Recommended Dosing Regimens
Adults and Adolescents (≥13 years)
- Oseltamivir: 75 mg once daily 1, 2
- Zanamivir: 10 mg (two 5-mg inhalations) once daily for patients ≥5 years 1
- Baloxavir: Single dose (FDA-approved November 2020), demonstrated 1% infection rate vs. 13% with placebo when given within 48 hours of exposure 1
Pediatric Patients (Weight-Based Dosing for Oseltamivir)
- ≤15 kg: 30 mg once daily 1, 2
- >15-23 kg: 45 mg once daily 1, 2
- >23-40 kg: 60 mg once daily 1, 2
- >40 kg: 75 mg once daily 1, 2
Infants (3-12 months)
- 3 mg/kg/dose once daily 1
Infants (<3 months)
- Not routinely recommended unless situation judged critical due to limited data 1
Duration of Chemoprophylaxis
- Post-exposure prophylaxis: 10 days following last exposure 1, 3, 2
- Seasonal/community outbreak prophylaxis: Up to 6 weeks during influenza activity 3, 2
- Immunocompromised patients: May extend up to 12 weeks during community outbreaks 2
- Institutional outbreaks: Minimum 2 weeks, continuing until approximately 1 week after outbreak ends 1
Critical Timing Considerations
Chemoprophylaxis must be initiated within 48 hours of exposure to be optimally effective 1. The protective effect lasts only as long as the medication is continued, and susceptibility returns when discontinued 1.
Institutional Outbreak Management
When confirmed or suspected outbreaks occur in institutions housing high-risk persons:
- Administer chemoprophylaxis to all residents regardless of vaccination status 1
- Offer to unvaccinated staff providing care to high-risk persons 1
- Consider for all employees if outbreak strain is poorly matched to vaccine 1
- Continue for minimum 2 weeks, extending if new cases continue to occur 1
Important Caveats and Pitfalls
Not a Vaccine Substitute
Chemoprophylaxis is not a substitute for annual influenza vaccination, which remains the primary prevention strategy 1, 2. The vaccine should always be offered when not contraindicated 1.
Resistance Considerations
- Amantadine and rimantadine are NOT recommended due to high resistance rates (>99%) among currently circulating influenza A viruses 1
- Currently circulating viruses remain >99% susceptible to oseltamivir, zanamivir, peramivir, and baloxavir 1
Live Attenuated Influenza Vaccine (LAIV) Interaction
Oseltamivir and other neuraminidase inhibitors likely decrease LAIV effectiveness if administered concurrently 1. However, antiviral use is not a contraindication to inactivated influenza vaccines 1.
Adverse Effects
- Nausea and vomiting occur in ~10-15% of oseltamivir recipients 3
- Taking with food reduces gastrointestinal side effects 3
- Patients should be informed that influenza risk is lowered but not eliminated during chemoprophylaxis 1
Renal Dose Adjustment
For creatinine clearance <30 mL/min: Reduce oseltamivir to 75 mg once every other day for prophylaxis 2
High-Risk Populations Requiring Special Consideration
Chemoprophylaxis combined with vaccination may be considered for: