Does oseltamivir (Tamiflu) reduce contagiousness?

Does Tamiflu Make You Less Contagious?

Yes, oseltamivir (Tamiflu) significantly reduces viral shedding and therefore makes you less contagious to others. Studies demonstrate that oseltamivir treatment reduces both the quantity and duration of viral shedding compared to placebo, with the most substantial reductions occurring when treatment is started within 48 hours of symptom onset 1, 2.

Evidence for Reduced Viral Shedding

Oseltamivir significantly reduces virus isolation at multiple time points during illness:

• In a randomized controlled trial in Bangladesh, oseltamivir reduced virus isolation by 15% on day 2 (66% placebo vs 56% oseltamivir, p=0.0004), by 30% on day 4 (43% vs 30%, p<0.0001), and by 48% on day 7 (12% vs 6%, p=0.0009) 2
• Studies in volunteers with experimental influenza showed that oseltamivir 20-200 mg twice daily for 5 days reduced both the quantity and duration of viral shedding compared with placebo 1
• In household contacts receiving prophylaxis, viral shedding was inhibited with 84% protective efficacy (95% CI, 57%-95%; P<0.001) 3

Timing Matters for Maximum Effect

Treatment initiated within 48 hours provides the greatest reduction in viral shedding:

• When treatment was started less than 48 hours after symptom onset, oseltamivir significantly reduced virus isolation on days 2,4, and 7 2
• When treatment was started 48 hours or longer after symptom onset, oseltamivir still significantly reduced virus isolation on days 2 and 4, but not day 7 2
• Data on whether viral shedding is reduced are somewhat inconsistent across studies, with one experimental infection study showing reduced duration of viral shedding, while other studies have not consistently demonstrated this reduction 4

Clinical Implications for Contagiousness

The reduction in viral shedding translates to meaningful protection of household contacts:

• Post-exposure prophylaxis with oseltamivir demonstrated 89% protective efficacy against clinical influenza in household contacts of infected persons (95% CI, 67%-97%; P<0.001) 3
• Oseltamivir prevented influenza outbreaks within households with 84% protective efficacy at the household level (95% CI, 49%-95%; P<0.001) 3
• The drug should be initiated within 48 hours of symptom onset in the infected person for optimal protection of contacts 3

Important Caveats

While oseltamivir reduces viral shedding, treated patients remain potentially contagious:

• Persons treated with oseltamivir can shed susceptible viruses early in treatment and may later shed drug-resistant viruses, including after 5-7 days of therapy 4
• The emergence of oseltamivir resistance during treatment is rare overall (<1%) but has been documented, particularly in children (18% in one Japanese study, though other studies show lower rates) 4, 2
• All virus isolates from oseltamivir recipients in the household contact study retained sensitivity to the active metabolite, suggesting resistance emergence was not a significant concern in that population 3

Practical Recommendations

To minimize transmission risk while on oseltamivir:

• Continue standard infection control measures (hand hygiene, respiratory etiquette, avoiding close contact with others) even while taking oseltamivir, as the drug reduces but does not eliminate viral shedding 5
• The standard 5-day treatment course should be completed as prescribed, with treatment discontinued 24-48 hours after symptom resolution 5
• Immunocompromised patients may experience prolonged viral shedding even after oseltamivir treatment and may require extended treatment duration beyond 5 days 4, 5