Influenza Strain Surveillance and Seasonal Patterns

Finding Current Strain Information

• The Centers for Disease Control and Prevention (CDC) recommends checking the CDC's FluView Interactive dashboard for weekly updated surveillance data on circulating influenza strains by region and state 1, 2
• The CDC and state health departments suggest contacting local health departments for real-time influenza surveillance reports to track predominant strains and activity levels 3, 4

Historical Patterns and Vaccine Effectiveness

• The American Academy of Pediatrics notes that influenza A(H1N1)pdm09, A(H3N2), and influenza B viruses have co-circulated in recent years, with the predominant strain varying by season 1, 6
• The CDC reports that H3N2-predominant seasons are typically associated with higher severity, increased hospitalizations, and greater mortality, particularly in young children and older adults 2, 7, 6
• The CDC states that influenza activity in the United States typically peaks between December and February, though peak activity can occur as late as April or May 8, 4

Clinical Importance of Real-Time Data

• The CDC indicates that vaccine effectiveness varies significantly by strain, with recent seasons showing vaccine effectiveness ranging from 9% against A(H3N2) to 76% against influenza B/Victoria in children 1, 6
• The American Academy of Pediatrics notes that H3N2 seasons are associated with higher pediatric mortality and hospitalization rates compared to H1N1 or B-predominant seasons 2, 7
• The CDC suggests that treatment decisions and chemoprophylaxis strategies may be influenced by local strain circulation patterns and resistance profiles 8