What is the recommended post-exposure prophylaxis (PEP) for influenza A?

Post-Exposure Prophylaxis for Influenza A

For post-exposure prophylaxis of influenza A, administer oseltamivir 75 mg once daily for 7-10 days after the last known exposure, initiated as soon as possible and ideally within 48 hours of exposure. 1

Timing and Initiation

• Start oseltamivir prophylaxis as soon as possible after exposure is identified, ideally no later than 48 hours after exposure 1
• Do not initiate once-daily prophylaxis if more than 48 hours has elapsed since exposure; instead, educate patients to start full-dose treatment immediately if symptoms develop 1
• The protective efficacy of oseltamivir for post-exposure prophylaxis ranges from 58.5% to 89% depending on the exposure setting 2

Standard Dosing Regimens

Adults and Adolescents (≥13 years)

• Oseltamivir 75 mg once daily for 7-10 days after last known exposure 1, 3
• In institutional outbreak settings, continue for minimum 14 days and for 7 days after the last known exposure 1

Pediatric Patients (1-12 years)

Weight-based dosing, once daily for 10 days: 1, 3

• ≤15 kg: 30 mg once daily

• 15-23 kg: 45 mg once daily

• 23-40 kg: 60 mg once daily

• 40 kg: 75 mg once daily

Infants (3-11 months)

• 3-8 months: 3 mg/kg once daily 1
• 9-11 months: 3.5 mg/kg once daily 1
• Prophylaxis is not generally recommended for infants <3 months due to limited safety data unless deemed critical for outbreak control 1

Preterm Infants

Prophylaxis is not generally recommended due to limited data unless essential for outbreak control 1

Alternative Agent: Zanamivir

• Zanamivir 10 mg (two 5-mg inhalations) once daily for 7-10 days is an alternative for patients ≥5 years 1
• Zanamivir should be the preferred agent for high-risk exposure groups when available, particularly for healthcare workers exposed to oseltamivir-treated H5N1 patients due to potential oseltamivir resistance 1
• Do not use zanamivir in patients with chronic respiratory diseases (asthma, COPD) due to bronchospasm risk 1

Risk-Stratified Approach

The strength of recommendation varies by exposure risk: 1

High-Risk Exposure Groups (Strong Recommendation)

• Household or close family contacts of confirmed influenza patients 1
• Healthcare personnel with unprotected close contact during high-risk procedures (intubation, suctioning) 1
• Severely immunocompromised persons for whom vaccination is contraindicated or expected to have low effectiveness 1

Moderate-Risk Exposure Groups (Weak Recommendation)

• Individuals with very close direct exposure to sick or dead H5N1-infected animals 1
• Healthcare workers with potentially inadequate personal protective equipment 1

Low-Risk Exposure Groups

• Prophylaxis should probably not be administered to low-risk individuals 1
• Pregnant women in low-risk groups should not receive prophylaxis (strong recommendation) 1

Special Populations

Immunocompromised Patients

• May continue prophylaxis for up to 12 weeks during community outbreaks 3
• This extended duration is particularly relevant for solid organ or hematopoietic stem cell transplant recipients 3

Pregnant Women

• Prophylaxis is recommended for pregnant women in high-risk and moderate-risk exposure groups 1
• Benefits typically outweigh risks when there is significant exposure 4

Unvaccinated Household Contacts

• Consider prophylaxis (in conjunction with vaccination) for unvaccinated household contacts of persons at very high risk of complications 1
• For high-risk individuals within 2 weeks of vaccination, prophylaxis is recommended as vaccine-induced immunity is not yet established 4

Important Considerations and Monitoring

• Prophylaxis does not interfere with antibody response to influenza vaccine 4
• Test for influenza and switch to treatment dosing (75 mg twice daily) if symptoms develop during prophylaxis, preferably using an antiviral with a different resistance profile 1
• Nausea occurs in approximately 10-15% of patients; taking oseltamivir with food reduces gastrointestinal side effects 5, 6
• Prophylaxis is not a substitute for annual influenza vaccination, which remains the primary prevention strategy 1, 3, 7

Common Pitfalls

• Avoid M2 inhibitors (amantadine, rimantadine) due to high resistance rates among current influenza A strains 5, 2
• Do not delay prophylaxis beyond 48 hours; instead, educate patients about early empiric treatment if symptoms develop 1
• Ensure proper dosing device for infants <1 year (use 3-mL or 5-mL oral syringe, not the standard dispenser) 1
• Adjust dosing in renal insufficiency; oseltamivir is not recommended for end-stage renal disease patients not on dialysis 3

Alternative Strategy

Educating patients about early empiric initiation of antiviral treatment (within 12-24 hours of symptom onset) can be considered as an alternative to post-exposure prophylaxis, particularly in settings where prophylaxis feasibility is limited 1, 6