Influenza Transmission and Prevention: Why the Flu Spreads and How to Protect Yourself

Transmission

• Primary: Respiratory droplets (>5 µm) from cough/sneeze/talk — travel <6 ft, land on mucosa.
• Airborne (aerosol): <5 µm particles remain suspended; important in enclosed, poorly ventilated spaces.
• Contact: Fomites (contaminated surfaces) → self-inoculation (touch face).

Contagious: 1 day before symptoms → 5–7 days after (longer in kids/immunocompromised).

Prevention

Vaccination (Cornerstone)

• Annual quadrivalent (IIV4, RIV4, LAIV4) — matches circulating strains.
• Effectiveness: 40–60% when well-matched; reduces severity, hospitalization, death even if breakthrough.
• Recommended for everyone ≥6 months (rare exceptions).
• High-dose/adjuvanted for ≥65.

Non-Pharmaceutical Interventions

• Hand hygiene (soap/water 20s or ≥60% ABHR).
• Masking in high-risk settings (N95/KN95 > surgical).
• Ventilation/filtration (HEPA, open windows).
• Stay home when sick (≥24h fever-free without antipyretics).
• Avoid close contact with ill.

Antivirals (Treatment / Post-Exposure Prophylaxis)

• Oseltamivir, baloxavir, zanamivir, peramivir.
• Start ≤48h symptom onset for maximal benefit.
• PEP for high-risk exposed (oseltamivir 75 mg daily ×7–10 days).