Pooled influenza vaccine effectiveness estimates for Australia, 2012-2014

Area of Science:

• Epidemiology
• Immunization
• Public Health

Background:

• Influenza remains a significant public health concern, necessitating ongoing evaluation of vaccine effectiveness.
• Sentinel surveillance networks are crucial for monitoring influenza activity and vaccine performance in real-world settings.
• Accurate estimation of influenza vaccine effectiveness (VE) is vital for informing public health policy and vaccination strategies.

Purpose of the Study:

• To estimate Australia-wide influenza vaccine effectiveness (VE) against laboratory-confirmed influenza.
• To analyze VE across different influenza seasons (2012, 2013, 2014) and circulating strains (A(H1N1)pdm09, A(H3N2), Influenza B).
• To assess the impact of pooling data from multiple surveillance networks on VE estimation precision.

Main Methods:

• Data were pooled from three Australian sentinel general practice influenza surveillance networks.
• Patients with influenza-like illness were tested for influenza; vaccination status was compared between positive and negative cases.
• Logistic regression was used to estimate VE, adjusting for age, presentation week, and surveillance network.

Main Results:

• Overall VE ranged from 38% in 2012 to 60% in 2013 and 44% in 2014.
• VE was higher in 2013 (60%) when A(H1N1)pdm09 dominated and vaccine match was good, compared to 2012 (38%) and 2014 (44%) when A(H3N2) predominated and vaccine match was poor.
• VE against Influenza B was consistently high across all years (54-57%).

Conclusions:

• Influenza vaccine effectiveness in Australia varied significantly by season, influenced by the dominant circulating strain and vaccine match.
• Pooling data from sentinel networks enhances sample size, enabling more precise subtype- and age-specific VE estimates.
• Findings underscore the importance of strain surveillance and vaccine composition for optimizing influenza vaccine effectiveness.