How Much is 13 Euros? Understanding Flu Vaccine Effectiveness in the 2012/13 Season

The 2012/13 influenza season in Europe saw significant co-circulation of influenza B, A(H1N1)pdm09, and A(H3N2) viruses. A multicentre case-control study, part of the Influenza Monitoring Vaccine Effectiveness in Europe (I-MOVE) project, was conducted across seven European Union member states to assess the effectiveness of the seasonal flu vaccine. This study aimed to determine how well the vaccine protected against medically attended influenza-like illness (ILI) confirmed by laboratory testing.

Measuring Vaccine Effectiveness Against Multiple Flu Strains

Researchers systematically collected samples from ILI patients within seven days of symptom onset. These samples were then analyzed to confirm the presence and type of influenza virus. The study compared individuals who tested positive for influenza with those who tested negative, focusing on cases meeting the EU ILI case definition. A comprehensive analysis, using logistic regression and controlling for factors like age, sex, and pre-existing conditions, was performed to calculate adjusted vaccine effectiveness (AVE).

Vaccine Effectiveness Results and Implications

A total of 7,954 records were initially collected. After applying exclusion criteria, 4,627 patients were included in the analysis for influenza B (1,937 confirmed cases), 3,516 for A(H1N1)pdm09 (1,068 cases), and 3,340 for A(H3N2) (730 cases).

The study found:

• AVE against influenza B: 49.3% (95% confidence interval [CI]: 32.4 to 62.0)
• AVE against A(H1N1)pdm09: 50.4% (95% CI: 28.4 to 65.6)
• AVE against A(H3N2): 42.2% (95% CI: 14.9 to 60.7)

These findings suggest a low to moderate overall effectiveness of the 2012/13 seasonal influenza vaccine against all three circulating strains. The large sample size allowed for specific analysis of each virus type/subtype.

Conclusion: The Need for Improved Flu Vaccines

The relatively low AVE estimates highlight the need for continuous improvement in seasonal influenza vaccines. Achieving higher protection levels is crucial for effectively mitigating the impact of influenza outbreaks, especially in seasons with multiple circulating strains. Further research and development are essential to enhance vaccine efficacy and ensure better public health outcomes. The cost of influenza, both in terms of human health and economic burden, underscores the importance of ongoing efforts to develop more effective vaccines.