Can Tamiflu Be Used for Prevention in People Exposed to the Flu?
Yes, oseltamivir (Tamiflu) is highly effective for post-exposure prophylaxis in people exposed to influenza, reducing the risk of developing symptomatic influenza by 89% when initiated within 48 hours of exposure to an infected person. 1, 2
Post-Exposure Prophylaxis Dosing
Standard prophylaxis regimen is oseltamivir 75 mg once daily for 10 days after the last known exposure in adults and adolescents ≥13 years. 3, 1
For pediatric populations, weight-based dosing applies: 1
- Children >40 kg: 75 mg once daily for 10 days
- Children >23-40 kg: 60 mg once daily for 10 days
- Children >15-23 kg: 45 mg once daily for 10 days
- Children ≤15 kg: 30 mg once daily for 10 days
- Infants 3-12 months: 3 mg/kg once daily for 10 days
- Infants <3 months: Not recommended unless situation is critical 1
When to Initiate Prophylaxis
Prophylaxis should be started for household or close contacts of a confirmed influenza patient, ideally within 48 hours of the index case developing symptoms. 1, 2 This timing is critical because household contacts face exposure to both the index case and common environmental sources. 1
Priority groups for prophylaxis include: 3, 1
- High-risk individuals who have not yet been vaccinated
- Persons within 2 weeks of receiving influenza vaccine (before full immunity develops)
- Immunocompromised patients
- Pregnant women with significant exposure
- Unvaccinated persons with frequent contact with high-risk individuals during community outbreaks
Efficacy Data
The evidence for post-exposure prophylaxis is robust. In household contact studies, oseltamivir demonstrated 89% protective efficacy for individuals and 84% protective efficacy for households in preventing laboratory-confirmed clinical influenza. 2 The CDC reports similar efficacy rates of 82-89% across multiple studies. 1
For pre-exposure (seasonal) prophylaxis during community outbreaks, oseltamivir reduced influenza incidence from 5% to 1% when taken for 42 days in healthy unvaccinated adults. 4 In vaccinated elderly nursing home residents, oseltamivir provided an additional 92% reduction in influenza illness beyond vaccination alone. 5
Duration of Prophylaxis
Post-exposure prophylaxis: 10 days after last known exposure 3, 1
Pre-exposure (seasonal) prophylaxis: Up to 6 weeks during periods of influenza activity in the community 3, 1 Regimens as long as 42 days have been studied and proven effective. 3, 4
For children receiving influenza vaccine for the first time, prophylaxis may need to extend for 6 weeks to cover the period until full vaccine immunity develops. 1
Important Clinical Considerations
Prophylaxis is not a substitute for vaccination, which remains the primary means of influenza prevention. 1 However, oseltamivir prophylaxis does not interfere with antibody response to influenza vaccine, making concurrent use appropriate. 1
Common pitfall: Gastrointestinal adverse events (nausea, vomiting) are the most common reason for discontinuation of prophylaxis. 3 In one study, only 48% of primary school children and 76% of secondary school children completed a full prophylaxis course, with GI symptoms being the primary reason for stopping. 3 Taking oseltamivir with food significantly improves GI tolerability. 6
Renal dosing adjustments are essential: For patients with CrCl 10-30 mL/min, reduce prophylaxis dose to 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 doses total). 6
Alternative Strategy: Early Treatment Approach
An alternative to routine prophylaxis is counseling exposed high-risk individuals about early influenza signs and symptoms, with instructions to contact their provider immediately for early treatment if symptoms develop. 3 This approach may be appropriate when early recognition and treatment access are feasible, though direct prophylaxis provides more reliable protection for high-risk contacts. 3
Pre-Exposure Prophylaxis Limitations
Pre-exposure prophylaxis should be reserved for very high-risk patients (e.g., severely immunosuppressed) who cannot otherwise be protected during high-risk exposure periods. 3 Prolonged use carries uncertain long-term adverse event risks and may select for antiviral resistance. 3 The CDC may recommend prioritizing treatment over prophylaxis if antiviral shortages are anticipated. 3
Tolerability Profile
In prophylaxis trials, oseltamivir increased the risk of: 7
- Headaches: 3.15% absolute increase (NNTH = 32)
- Nausea: 4.15% absolute increase (NNTH = 25)
- Psychiatric adverse events: 1.06% absolute increase (NNTH = 94)
- Renal events: 0.67% absolute increase (NNTH = 150)
These effects are generally mild and transient, and the drug was well tolerated in long-term studies extending up to 6 weeks. 5