What treatment is recommended for individuals exposed to influenza?

Post-Exposure Influenza Prophylaxis

For individuals exposed to influenza, antiviral chemoprophylaxis with oseltamivir, zanamivir, or baloxavir should be initiated within 48 hours of exposure, but only for specific high-risk groups—not routinely for all exposed persons. 1

Who Should Receive Post-Exposure Prophylaxis

Antiviral chemoprophylaxis is recommended in the following specific situations after known or suspected influenza exposure:

High-Priority Groups for Prophylaxis

• Children at high risk of complications for whom influenza vaccine is contraindicated 1

• Children at high risk during the 2 weeks after influenza vaccination, before optimal immunity is achieved 1

• Unvaccinated family members or healthcare personnel who have ongoing, close exposure to:

  • Unvaccinated children at high risk 1
  • Unvaccinated infants and toddlers younger than 24 months 1

• Immunocompromised children as a supplement to vaccination, since they may not respond with sufficient protective immune responses after vaccination 1

• Family members and close contacts of an infected person if those persons are at high risk of complications from influenza 1

• For outbreak control in institutional settings with unvaccinated staff and children at high risk (e.g., extended-care facilities) 1

• When circulating strains are not matched with vaccine strains, for children at high risk and their family members, close contacts, and healthcare personnel 1

Recommended Antiviral Agents for Prophylaxis

First-Line Options

Oseltamivir (oral) is the most widely studied and preferred agent for prophylaxis:

• Adults and adolescents ≥13 years: 75 mg once daily for at least 10 days following close contact, up to 6 weeks during community outbreak 2
• Pediatric dosing (1-12 years): Weight-based once daily dosing 3, 2
  • ≤15 kg: 30 mg once daily
  • 15.1-23 kg: 45 mg once daily
  • 23.1-40 kg: 60 mg once daily

  • 40 kg: 75 mg once daily

• Immunocompromised patients: May continue up to 12 weeks 2

Zanamivir (inhaled) is an acceptable alternative:

• Lower once-daily dosing for prophylaxis 1
• Should not be used in patients with chronic respiratory disease 3

Baloxavir received FDA approval in November 2020 for chemoprophylaxis:

• Single dose within 48 hours of exposure for household members ≥12 years 1
• Reduced influenza development from 13% (placebo) to 1% in Japanese study 1
• Well tolerated in randomized trials 1
• Dosing: Weight-based single dose (40 mg for 20-<80 kg; 80 mg for ≥80 kg) 4

Agents NOT Recommended

Amantadine and rimantadine should not be used due to high levels of resistance among currently circulating influenza A viruses 1

Critical Timing and Decision Factors

Optimal timing: Postexposure chemoprophylaxis should only be used when antiviral agents can be started within 48 hours of exposure 1

Key Decision Factors

Decisions on whether to administer chemoprophylaxis should account for:

• The exposed person's risk of influenza complications 1
• Vaccination status 1
• Type and duration of contact 1
• Recommendations from local or public health authorities 1
• Clinical judgment 1

Important Caveats and Pitfalls

Prophylaxis vs. Treatment Dosing

Do not confuse prophylaxis and treatment doses: The lower once-daily dosing for chemoprophylaxis with oral oseltamivir or inhaled zanamivir should NOT be used for treatment of symptomatic children 1

For high-risk symptomatic patients: Use early full treatment doses (rather than chemoprophylaxis doses) without waiting for laboratory confirmation 1

Not a Substitute for Vaccination

Chemoprophylaxis should not be considered a substitute for vaccination 1. The influenza vaccine should always be offered before and throughout the influenza season when not contraindicated 1

Drug Interactions

Avoid coadministration of baloxavir with:

• Dairy products
• Calcium-fortified beverages
• Polyvalent cation-containing laxatives, antacids, or oral supplements (calcium, iron, magnesium, selenium, zinc) 4

Live Attenuated Influenza Vaccine (LAIV) Considerations

LAIV effectiveness will be decreased for children receiving oseltamivir or other influenza antiviral agents 1. Antiviral use is not a contraindication to inactivated influenza vaccines (IIVs) 1

Patient Counseling

Inform recipients that:

• Risk of influenza is lowered but still remains while taking the medication 1
• Susceptibility to influenza returns when medication is discontinued 1
• Potential adverse effects: Oseltamivir may cause nausea/vomiting (especially in children); baloxavir is generally well tolerated 1, 3

Current Resistance Patterns

During the 2019-2020 influenza season, >99% of influenza A(H1N1)pdm09 and B/Victoria viruses tested were susceptible to oseltamivir, peramivir, and zanamivir, and all were susceptible to baloxavir 1. Decreased susceptibility to baloxavir has been reported in Japan where its use has been more common, with ongoing surveillance in Japan and the United States 1